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SPECTRUM  ANALYSIS. 


BARIUM 


Cyclopedic  Science 
Simplified. 


BY 

J.  H.  PEPPER, 

Late  Professor  of  Chemistry  and  Honorarj'  Director  of  the  Royal  Polytechnic  Institution,  Fellow 
of  the  Chemical  Society,  Associate  of  the  Institution  of  Civil  Engineers, 

Author  of  various  Works  f  >r  Youth,  etc. 


EMBRACING 


LIGHT 

Reflection  and  Refraction  of  Light 
Light  and  Color 
Spectrum  Analysis 
The  Human  Eye 
Polarized  Light 
HEAT 

Thermometric  Heat 
Conduction  of  Heat 
Latent  Heat 
Steam 

ELECTRICITY 

Voltaic,  Galvanic,  or  Dynamical 
Electricity 


MAGNETISM 

Electro-Magnetism,  Magneto-Elec 
tricity,  Thermo-Electricity 
Dia-Magnetism 
Wheatstone's  Telegraphs 

PNEUMATICS 
The  Air-Pump 
The  Diving-Bell 

ACOUSTICS 

The  Education  of  the  Ear 

CHEMISTRY 

Elements  which  are  not  Metallic 
The  Metals 


WITH  SIX  Hi'NDRED  ILLUSTRATIONS. 


PHILADELPHIA: 

J.  B.  LIPPINCOTT  COMPANY. 


PUBLISHERS’  PREFACE. 


The  general  demand  for  works  of  science  written  in  such 
a  manner  as  to  be  easily  understood  by  the  young,  as  well 
as  by  persons  not  specially  trained  in  scientific  pursuits,  has 
seemed  to  the  Publishers  to  justify  the  reprinting  of  this 
highly  successful  English  work.  Its  style  is  lucid,  while  in 
point  of  scientific  exactness  nothing  is  wanting.  A  notable 
feature  is  the  comparative  absence  of  purely  technical  terms. 
The  work  is,  in  reality,  a  hand-book  of  instructive  experi¬ 
ments,  chiefly  in  physics  and  chemistry.  Only  such  changes 
have  been  made  in  the  present  edition  as  were  found  neces¬ 
sary  to  fit  the  work  more  completely  for  the  American  stu¬ 
dent’s  use. 

The  reader  will  find  portions  of  valuable  papers  written  by 
Faraday,  Daniell,  Wheatstone,  Brewster,  Tyndall,  Crookes, 
Browning,  Siemens,  Noad,  Stewart,  Tait,  Marloye,  and  others, 
with  a  brief  summary  of  Photography  by  John  Spiller,  Esq. 


Contents. 


LIGHT. 

Page 

LIGHT,  and  the  Ether  supposed  to 


Ii  I G  H  T — continued. 

Page 

THE  REFRACTION  OF  LIGHT  .  69 


PERVADE  THE  WHOI.E  UNIVERSE .  I 

Corpuscular  Theory  of  Light  .  2 

Experiments  with  blacked  Aluminium 

Disc .  4 

On  Attraction  and  Repulsion  re¬ 
sulting  from  Radiation  .  5 

Application  of  the  Direct  Rays  of 

the  Sun  as  a  Motive  Power  .  14 

SOURCES  OF  LIGHT  .  19 

Heat  a  Source  of  Light  .  21 

Light  the  frequent  attendant  of 

Electrical  Phenomena .  21 

Author’s  Experiments  with  the 
Great  Induction  Coil  at  the 

Royal  Polytechnic  .  22 

Description  of  a  large  Induction 

Coil  .  27 

Chemical  Combination  a  Source  of 

Light  . 30 

Is  Mechanical  Force  to  be  regarded 

as  a  true  Source  of  Light?  .  31 

THE  DIFFUSION  OF  LIGHT  .  33 

Modifications  that  Light  may  un¬ 
dergo  .  40 

THE  REFLECTION  OF  LIGHT  .  40 

The  Ghost  Illusion .  44 

Images  formed  by  Silvered  Mirrors  47 

The  Kaleidoscope  .  51 

Thh  Japankse  Magic  Mirror .  55 

Browning’s  Description  of  the  Sil¬ 
vered  Glass  Reflecting  Tele¬ 
scopes  .  61 


Dioptrics  .  69 

Refraction  of  Light  through  Plane 

Glass  .  73 

Refraction  of  Parallel  Rays  of 

Light  by  Convex  Surfaces  .  73 

Refraction  of  Parallel  Rays  by 

Concave  Surfaces .  74 

Other  forms  of  Lenses .  74 

OPTICAL  INSTRUMENTS  WHOSE 
PROPERTIES  DEPEND  ON  RE¬ 
FRACTION  .  75 

The  Simple  and  Compound  Micro¬ 
scope  and  Telescope  .  75 

The  Camera  Obscura .  77 

THE  HUMAN  EYE  .  84 

THE  STEREOSCOPE .  88 

Professor  Wheatstone’s  Reflecting 

Stereoscope  .  88 

Directions  for  using  the  Stereo¬ 
scope .  91 

PERSISTENCE  OF  VISION .  91 

LIGHT  AND  COLOUR  .  106 

SPECTRUM  ANALYSIS  .  106 

Aberration  and  Achromatism  .  106 

Mode  of  using  the  Heliostat  .  109 

Physical  Properties  of  the  Spec¬ 
trum  .  1 13 

The  Dark  or  Fixed  Lines  in  the 

Solar  Spectrum .  114 

How  to  use  the  Spectroscope  .  117 

V 


VI 


CONTENTS. 


Li  I G  H  T — continued. 

Page 

Spherical  Aberration .  125 

(The  Dispersion  of  Light,  or  Chro¬ 
matic  Aberration . .  126 


THE  INTERFERENCE  OF  LIGHT...  128 
Colours  of  Thin  Plates  .  128 


LIGH  T — continued. 

Page 

DOUBLE  REFRACTION  AND  THE 

POLARIZATION  OF  LIGHT .  133 

Polarization  by  Reflection  and  by 

Simple  Refraction  .  136 

Polarization  by  the  Tourmaline .  138 


HEAT. 

THERMOMETRIC  HEAT  .  146 

The  common  Effects  of  Heat  .  151 

Amount  of  Expansion  in  Solids, 
Liquids,  and  Gases  .  154 

THE  EXPANSION  OF  LIQUIDS .  156 

The  Thermometer .  159 

Negretti  and  Zambra’s  Recording 

and  Deep-Sea  Thermometer  .  163 

The  Pyrometer  .  166 

THE  EXPANSION  OF  GASES  .  169 

CONDUCTION  .  174 

“Potential”  Force .  178 

"Actual”  Force,  or  “Energy”  .  178 


H  E  A  T —continued. 

LATENT  HEAT  .  187 

Energy  or  Heat  .  188 

Capacity  for  Heat  .  191 

STEAM  .  199 

THE  STEAM  ENGINE  .  207 

Description  of  the  Steam  Engine...  210 
EVAPORATION .  221 

HYGROMETRY  .  222 

RADIATION .  224 

TRANSMISSION  OF  HEAT .  228 

The  Conversion  of  Light  Rays  into 
Heat  Rays,  and  vice  versa,  by 
CHANGE  OF  ReFRANGIBILITY  .  230 


ELECTRICITY. 

ELECTRICITY,  FRICTIONAL  OR 

STATICAL .  235 

The  Electroscope .  236 

THEORIES  OF  ELECTRICITY  .  241 

EXPERIMENTS  WITH  THE  ELEC¬ 
TROSCOPE  .  242 


ELECTRICAL  MACHINES  .  248 

ELECTRICAL  ATTRACTION  AND 
REPULSION  GOVERNED  BY 

CERTAIN  LAWS .  255 

The  Electric  Well .  262 

ELECTRICAL  INDUCTION .  264 

The  Electrophorus .  273 

The  Leyden  Jar .  277 

Experiments  with  the  Electrical 
Machine,  the  Leyden  Jar,  and 
Leyden  Battery .  285 


ELECTRICIT  Y — continued. 

The  Hydro-Electric  Machine  .  302 

SUMMARY  OF  THE  LAWS  OF  ELEC¬ 
TRICAL  ACCUMULATION  .  309 

Lateral  Discharge .  314 

VOLTAIC,  GALVANIC,  OR  DYNAMI¬ 
CAL  ELECTRICITY. .  315 

Dynamical  Electrical  Phenomena 
obtained  from  the  Voltaic  Bat¬ 
tery  .  341 

“FARADAY’S  RESEARCHES"  .  345 

On  a  New  Measurer  of  Volta-Elec- 

tricity .  348 

Ohm’s  Law .  356 

The  Rheostat  of  Wheatstone .  359 

The  Calorific  Effects  of  the  Vol¬ 
taic  Current  .  365 

The  Electric  Torpedo  .  371 

The  Electric  Lamp .  374 


CONTENTS. 


Vll 


MAGNETISM. 

Page 

THE  MAGNET .  379 

DIA-MAGNETISM .  394 

ELECTRO-MAGNETISM  .  400 

MAGNETO-ELECTRICITY  .  408 

INDUCTION  BY  CURRENT  ELEC¬ 
TRICITY  .  408 

THERMO-ELECTRICITY .  419 

C.  and  L.  Wray’s  Patent  Thermo- 
Electric  Pile .  421 


WHEATSTONE’S  TELECRAPHS 


MAGNETIS  M  —continued. 

Page 


Improvements  in  Electric  Tele¬ 
graphs,  and  in  Apparatus  con¬ 
nected  THEREWITH .  440 

SIR  CHARLES  WHEATSTONE’S  LAST 
TELEGRAPHIC  APPARATUS  .  446 

THE  ATLANTIC  TELEGRAPH  CABLE  454 
The  Differential  Resistance  Mea¬ 
surer .  456 

On  Telephony .  463 

THE  TELEPHONE  .  464 

On  the  Conservation  of  Force  .  470 


PNEUMATICS. 

PNEUMATICS  .  473 

The  Air-Pump  .  474 

The  Diving-Bell  .  484 

EXPERIMENTS  WITH  THE  AIR- 
PUMP  .  491 


PNEUMATIC  S — continued. 

THE  BAROMETER .  493 

Admiral  Fitzroy’s  Weather  Guide...  495 

Water-Pumps  .  502 

The  Pneumatic  Lever .  510 


ACOUSTICS. 

ACOUSTICS .  516 

Marloye’s  Introduction  to  Cheval- 

lier’s  Catalogue  .  517 

On  the  Education  of  the  Ear .  523 

Considerations  on  Sound .  527 

Project  of  Study  concerning  the 
Acoustics  of  Public  Buildings  ...  532 
"On  the  Sounds  produced  by  Flame 

in  Tubes,  &c.” .  545 

Experiments  on  the  Sympathetic 
Resonance  of  Tuning-Forks  .  548 

VIBRATIONS  OF  STRINGS,  RODS, 
PLATES,  AND  COLUMNS  OF  AIR  551 
Longitudinal  Vibrations  of  Strings  552 
Longitudinal  Vibrations  of  Rods  ...  553 
Vibrating  Plates  . .  554 


ACOUSTIC  S —continued. 

Transverse  Vibrations  of  Blades  and 

Rods .  554 

Longitudinal  Vibrations  of  Columns 

of  Air .  555 

Embouchures  .  557 

THE  REFLECTION,  REFRACTION, 

&c.,  OF  SOUNDS .  558 

Tisley’s  Compound  Pendulum .  562 

The  Tuning-Fork  as  a  Telegraphic 

Instrument  .  565 

THE  TRANSMISSION  OF  SOUNDS 
THROUGH  GASEOUS,  LIQUID, 

AND  SOLID  MEDIA .  566 

Transmission  of  Sound  through 

Liquids .  5^9 

Transmission  of  Sound  through 
Solid  Conductors .  569 


vm 


CONTENTS. 


CHEMISTRY. 

Page 


CHEMISTRY  .  576 

Oleography  :  being  a  process  for  the 
Utilization  of  Tomlinson’s  Co¬ 
hesion  Figures  .  580 

Exhibiting  Cohesion  Figures  to  a 
Lecture  Audience .  582 

CHEMICAL  ACTION  .  586 

NOMENCLATURE .  588 

ELEMENTS  WHICH  ARE  NOT  ME¬ 
TALLIC . .  593 

OXYGEN  .  593 

The  Properties  of  Oxygen .  597 

Remarks .  598 

Ozone  .  598 

NITROGEN .  600 

HYDROGEN  .  604 

Nitrogen  and  Hydrogen,  Ammonia...  618 

THE  HALOGENS. 

CHLORINE .  620 

IODINE .  622 

The  Art  of  Photography .  623 

BROMINE .  627 

FLUORINE  .  628 

CARBON  . . .  629 


“On  the  Pressure  Cavities  in  Topaz, 
Beryl,  and  Diamond,  and  their 
bearing  on  Geological  Theories”  633 
Compounds  of  Carbon  with  Oxygen..  634 


Carbonic  Oxide  .  638 

Compounds  of  Carbon  with  Hydrogen  638 

BORON  . 639 

SILICON  .  641 

How  Gems  are  Manufactured .  644 

The  Sand-blast  Process  .  646 

SELENIUM .  648 

SULPHUR  .  649 

Compounds  of  Sulphur  with  Hydrogen  653 

PHOSPHORUS  . 654 

Red  Phosphorus .  659 

THE  METALS. 

TELLURIUM  .  662 

ARSENIC  .  663 


CHEMISTK  Y — continued. 

Page 


Sources  of  Arsenic  .  663 

Physical  Qualities  of  Arsenic .  663 

Chemical  Properties  of  Arsenic .  664 

ANTIMONY .  667 

Sources  whence  Derived  .  667 

Physical  Properties  of  Antimony  ...  668 
Chemical  Properties  of  Antimony...  668 

BISMUTH .  668 

Sources  whence  Derived  .  668 

Physical  Properties  of  Bismuth .  669 

Chemical  Properties  of  Bismuth .  669 

CLASSIFICATION  OF  THE  METALS  670 
Class  I. 

POTASSIUM .  671 

Sources  whence  Derived  .  671 

Physical  Properties  of  Potassium  ...  672 
Chemical  Properties  of  Potassium...  672 

SODIUM .  673 

Sources  whence  Derived  .  673 

Physical  Properties  of  Sodium .  673 

Chemical  Properties  of  Sodium  .  674 

RUBIDIUM  .  674 

CzESIUM  .  674 

LITHIUM .  675 

AMMONIUM  .  675 

Class  II. 

CALCIUM .  676 

STRONTIUM  .  676 

BARIUM . . .  677 

Class  III. 

ALUMINIUM .  677 

Class  IV. 

MAGNESIUM .  680 

ZINC . 683 

Sources  whence  Derived  .  683 

Physical  Properties  of  Zinc .  684 

Chemical  Properties  of  Zinc .  684 

CADMIUM  .  684 

Class  V. 

IRON  .  685 

Sources  whence  Derived .  685 

Physical  Properties  of  Iron .  691 

"Chemical  Properties  of  Iron .  691 


CONTENTS. 


ix 


CHEMISTR  Y— continued. 

Page 


MANGANESE .  692 

COBALT .  692 

NICKEL .  693 

CHROMIUM  .  693 

URANIUM  .  693 

INDIUM .  694 

Class  VI. 

TIN  .  694 

TITANIUM  .  694 

NIOBIUM .  694 

TANTALUM .  694 

Class  VII. 

TUNGSTEN .  695 


CHEMISTR  Y — continued. 

Class  VIII.  Page 

ARSENIC,  ANTIMONY,  AND  BIS¬ 
MUTH .  695 

Class  IX. 

LEAD  .  696 

THALLIUM .  696 

Class  X. 

SILVER  .  698 

COPPER .  702  t 

MERCURY  .  704 

Class  XI. 

PLATINUM .  704 

GOLD  .  7°5 

How  Jewellery  is  made  by  Ma¬ 
chinery  .  706 


♦ 


ORGANIC  CHEMISTRY. 

ORGANIC  ANALYSIS  .  711 

Dr.  Richardson’s  Experiments  in  Or¬ 
ganic  Decomposition  .  714 


ORGANIC  CHEMISTRY— continued. 
Exposure  of  Animal  Substances  to 
Water  Gas  at  a  High  Tempera¬ 
ture .  714—718 


ON  LIGHT, 

AND  THE  ETHER  SUPPOSED  TO  PERVADE  THE  WHOLE 

UNIVERSE. 

ABOUT  two  hundred  years  ago  Descartes,  Hook,  and  Huygens,  three  of 
the  most  celebrated  mathematicians  of  their  day,  entertained  the  idea 
that  light  was  propagated  by  the  vibrations  and  undulations  of  a  subtile 
elastic  fluid  called  ether,  which  not  only  filled  infinite  space,  but  was  con¬ 
tained  in  all  solid,  fluid,  and  gaseous  bodies.  The  immortal  Newton,  who 
was  opposed  to  this  theory,  or  at  least  created  one  of  his  own,  usually  called 
the  Corpuscular  Theory  of  Light,  appears  to  have  entertained  the  opinion 
(according  to  Enfield)  that  “All  fixed  bodies,  when  heated  beyond  a  certain 
degree,  emit  light  and  shine;  and  this  emission  is  performed  by  the  vibrating 
motion  of  their  parts.” 

“The  heat  of  a  warm  room  is  conveyed  through  a  vacuum  by  the  vibration 
of  a  much  subtiler  medium  than  air,  which,  after  the  air  is  drawn  out,  remains 
in  the  vacuum. 

“  It  is  by  the  vibrations  of  this  medium  that  light  is  refracted  and  reflected, 
and  heat  communicated.  This  medium  is  exceedingly  more  elastic  and  active, 
as  well  as  subtile,  than  the  air;  it  readily  pervades  all  bodies,  and  is  by  its 
elastic  force  expanded  through  the  heavens.  Its  density  is  greater  in  free  and 
open  space  than  in  compact  bodies,  and  increases  as  it  recedes  from  them. 
This  medium,  growing  denser  and  denser  perpetually  as  it  passes  from  the 
celestial  bodies,  may,  by  its  elastic  force,  cause  the  gravity  of  those  great 
bodies  towards  one  another,  and  of  their  parts  towards  the  bodies.  Vision, 
hearing,  and  animal  motion  may  be  performed  by  the  vibrations  of  this  sub¬ 
tile  elastic  fluid  or  ether.” 


V 


1 


2 


ON  LIGHT. 


These  opinions  would  seem  to  show  that  Newton  believed  all  emanations 
of  particles  of  light  were  attended  by  the  undulations  of  an  ethereal  medium 
accompanying  it  in  its  passage. 

(  The  theory,  however,  generally  ascribed  to  him  is,  that  rays  of  light  are 
small  corpuscles  emitted  with  exceeding  celerity,  travelling  at  about  the  rate  of 
one  hundred  and  eighty-six  thousand  miles  per  second;  and  these  rays  of 
light,  falling  upon  the  eye,  excite  vibrations  in  the  tunica  retina ,  which,  being 
propagated  along  the  solid  fibres  of  the  optic  nerve  to  the  brain,  cause  the 
sense  of  sight. 

Could  Newton,  who  insisted  so  much  on  the  importance  of  experimenting 
before  enunciating  a  theory,  have  been  acquainted  with  the  highly  interesting 
experiments  connected  with  the  inflection  or  diffraction  of  light,  he  would  not 
have  opposed  the  notion  of  an  analogy  between  the  phenomena  of  light  and 
sound  when  he  says:  “The  waves,  pulses,  or  vibrations  of  the  air,  wherein 
sound  consists,  are  manifestly  inflected,  though  not  so  considerably  as  the 
waves  of  water ;  and  sounds  are  propagated  with  equal  ease  through  crooked 
tubes  and  through  straight  lines ;  but  light  was  never  known  to  move  in  any 
curve,  nor  to  inflect  itself  ad  umbrani .”  This  decided  statement  is  directly 
contradicted  by  actual  experiment,  because  light  can  be  bent  into  or  towards 
the  shadow. 

The  corpuscular  theory  fails  to  explain  that  which  is  easily  understood  by 
the  undulatory  theory,  and  by  analogy  to  waves  of  water  or  air,  that  two  rays 
of  light  may  come  together  in  a  special  manner  and  produce  darkness ,  just  as 
two  waves  of  water  may  interfere  with  each  other  and  form  a  smooth  surface, 
or  two  waves  of  sound  produce  silence.  Dismissing  the  theory  of  Newton  as 
we  might  pass  by  the  venerable  ruins  of  some  ancient  edifice,  with  mingled 
interest  and  regret,  we  may  return  to  the  consideration  of  the  ether  supposed 
to  fill  all  space. 

The  great  Dr.  Franklin,  in  a  letter  dated  23rd  April,  1752,  throws  out  the 
suggestion  that  all  the  phenomena  of  light  may  be  more  conveniently  solved 
by  supposing  universal  space  filled  with  a  subtile  elastic  fluid,  which  when  at 
rest  is  not  visible,  but  whose  vibrations  affect  that  fine  sense  in  the  eye  as 
those  of  air  do  the  grosser  organs  of  the  ear. 

Thornbury,  Mitchell,  and  others,  endeavoured  to  prove  the  materiality  cf 
light  by  showing  that  the  corpuscles  had  a  power  of  momentum  which  might 
affect  other  and  very  light  substances.  Could  this  fact  have  been  really  ascer¬ 
tained,  there  would  be  nothing  more  to  say  against  Newton’s  hypothesis;  but 
their  experiments  were  illusory  and  useless.  On  the  other  hand,  the  supporters 
of  the  undulatory  theory  have  within  the  last  three  years  performed  the  most 
elaborate  and  exact  experiments  to  try  to  prove  the  real  existence  of  the  ether. 
Mr.  Balfour  Stewart,  F.R.S.,  superintendent  of  Kew  Observatory,  and  Pro¬ 
fessor  P.  G.  Tait,  M.A.,  of  Edinburgh,  whilst  leaving  other  scientific  men  to  make 
their  own  deductions  from  the  results  they  obtained,  have  called  attention  to 
the  subject  by  a  paper  read  before  the  Royal  Society  in  June,  1865,  and 
modestly  entitled  “  On  the  Heating  of  a  Disc  by  Rapid  Rotation  in  vacuo.” 
The  authors,  having  obtained  certain  results  in  air,  were  encouraged  to  construct 
the  apparatus  as  figured  below,  Fig.  1,  wherewith  to  procure  rotation  in  vacuo.* 

“  In  this  apparatus  a  slowly  revolving  shaft  is  carried  up  through  a  baro- 


*  In  the  article  on  Mr.  Crookes’s  “  Radiometer,”  it  will  be  seen  that  “  vacua  ”  are  of  three  kinds,  and 
it  would  greatly  enhance  the  value  of  these  experiments  if  the  aluminium  disc  was  rotated  in  the  most 
perfect  of  all  vacuums,  viz.,  “a  chemical  vacuum." 


ON  LIGHT. 


3 


meter  tube,  having  at  its  top  the  receiver  which  is  to  be  exhausted.  When  the 
exhaustion  has  taken  place,  the  shaft  connected  with  the  multiplying  gear 
revolves  in  mercury.  The  train  of  toothed  wheels  causes  the  disc  of  alumi- 


Fig.  r. 


a,  Figs,  i  and  2,  thermo-electric  pile  with 
reflecting  cone  attached  ;  a  b,  height  6  in.  from 
bed-plate  ;  a  c,  length  of  cone,  &c.,  5*  in.  ; 
c  d,  diameter  of  the  aperture  of  the  reflecting 
cone,  2}  in.  ;  f  It,  the  disc  of  aluminum  13  in. 
diameter  ;  eg,  height  from  bed  plate  to  centre 
of  the  aluminum  disc  8A  in. ;  b  e,  distance  of 
centre  of  the  thermo-electric  pile  from  the  disc 
of  aluminum  8  in. ;  m,  base  containing  the 
multiplying  gear;  sss,  air-tight  glass  receiver, 
15  in.  diameter  and  16  in.  high,  covering  the 
whole. 


Fig.  2. 


nium  to  revolve  125  times  for  each  revolution  of  the  shaft.  The  thei  mo-clectric 
pile,  the  most  delicate  thermometer  or  test  of  heat,  is  connected  by  two  wiies 
tarried  through  two  holes  in  the  bed-plate  of  the  receiver  with  a  1  hompson  s 
reflecting  galvanometer  needle  (an  instrument  which  is  described  and  figured 

1 — 2 


4 


ON  LIGHT. 


in  the  article  on  Electricity  in  this  work).  The  outside  of  the  thermo-electric 
pile  and  its  attached  cone  was  wrapped  round  with  wadding  and  cloth,  so  as 
to  be  entirely  unaffected  by  currents  of  air. 

“  During  these  experiments  the  disc  of  aluminium  was  rotated  rapidly  for  hall 
a  minute,  and  a  heating  effect  was,  in  consequence  of  the  rotation,  recorded 
by  the  thermo-electric  pile  (an  instrument  described  fully  in  the  article  on 
Electricity). 

“  To  obviate  the  objection  that  the  electric  currents  which  take  place  in  a 
revolving  metallic  disc  might  alter  the  zero  of  the  galvanometer,  the  position 
of  the  line  of  light  was  read  before  the  motion  began,  and  immediately  after 
it  ceased,  the  difference  being  taken  to  denote  the  heating  effect  produced  by 
the  rotation. 

“  The  thermometric  value  of  the  indications  given  by  the  galvanometer  was 
found  in  this  way: — The  disc  was  removed  from  its  attachment  and  laid  upon 
a  mercury  bath  of  known  temperature.  It  was  then  attached  to  its  spindle 
again,  being  in  this  position  exposed  to  the  pile,  and  having  a  temperature 
higher  than  that  of  the  pile  by  a  known  amount.  The  deflection  produced 
by  this  exposure  being  divided  by  the  number  of  degrees  by  which  the  disc 
was  hotter  than  the  pile,  gives  at  once  the  value  in  terms  of  the  galvanometric 
scale  of  a  heating  of  the  disc  equal  to  i°  on  Fahrenheit’s  scale. 

“The  disc  of  aluminium  being  blackened  with  a  coating  of  lampblack,  ap¬ 
plied  by  negative  photographic  varnish,  and  rock  salt  inserted  in  the  cone, 
the  following  results  were  obtained  : 


No  of 

No.  of  observations 

Time  at 

Heat  indications 

set. 

in  each  set. 

full  speed. 

0  Fahrenheit. 

1. 

3 

30 

o-85 

11. 

4 

30 

C87 

111. 

4 

30 

o-8i 

IV. 

3 

30 

075 

“  To  ascertain  whether  the  radiant  heat  recorded  was  derived  from  the  rock 
salt,  or  from  heated  air,  or  from  the  surface  of  the  disc,  the  next  series  of 
experiments  were  tried. 

Experiments  with  blacked  Aluminium  Disc  without  Rock  Salt. 


No.  of 

No.  of  observations 

Time  at 

Heat  indications 

set. 

in  each  set. 

full  speed. 

0  Fahrenheit. 

V. 

a 

30 

0-92 

VI. 

3 

30 

°'93 

“With  certain  modifications  of  the  above  experiments  it  was  satisfactorily 
proved  that  the  effect  was  not  due  to  heating  of  the  rock  salt,  or  to  radiation 
from  heated  air  ;  it  must  therefore  be  due  to  the  disc  of  aluminium,  which 
seemed  to  have  rubbed  against  some  matter  which  remained  in  the  receiver 
after  the  air  was  removed.  The  question  being,  was  this  ether?” 

The  authors  further  state  that, 

“  i. — It  may  be  due  to  the  air  which  cannot  be  entirely  got  rid  of. 

“2. — It  is  possible  that  visible  motion  becomes  dissipated  by  an  etherial 
medium  in  the  same  manner  and  possibly  to  nearly  the  same  extent 
as  molecular  motion,  or  that  motion  which  constitutes  heat. 

“  3- — Or,  the  effect  may  be  due  partly  to  air  and  partly  to  ether. 

“Not  to  leave  the  matter  wholly  undecided,  it  wss  suggested  by  Professors 


ON  LIGHT. 


5 


Maxwell  and  Graham  that  there  is  another  effect  of  afr,  viz.,  fluid  friction, 
the  coefficient  for  which  they  believe  to  be  independent  of  the  tension. 

“  It  would  appear,  however,  that  the  fluid  friction  of  hydrogen  is  much  less 
than  that  of  atmospheric  air,  so  that  were  the  heating  effect  due  to  fluid  fric¬ 
tion  it  ought  to  be  less  in  a  hydrogen  vacuum.  An  experiment  proved  that 
the  heating  effect  due  to  rotation  in  a  hydrogen  vacuum  was  22'5,  while  in  an 
air  vacuum  it  was  23  5,  and  the  authors  are  inclined  to  consider  these  numbers 
as  sensibly  the  same,  and  that  the  experiment  indicates  that  the  effect  is  not  due 
to  fluid  friction  ;  at  the  same  time  they  do  not  suppose  that  their  experiments 
have  yet  conclusively  decided  the  origin  of  this  heating  effect,  but  they  hope 
to  elicit  the  opinions  of  those  interested  in  the  subject,  which  may  serve  to 
direct  their  future  research.” 

These  experiments  are  more  satisfactory  than  any  previously  tried,  and, 
taken  in  conjunction  with  other  facts,  such  as  the  temporary  phosphorescence 
of  certain  bodies  by  what  is  termed  insolation  or  irradiation,  or  the  action  of 
light  in  reducing  certain  salts  to  their  metallic  state,  or  the  elaborate  and 
beautiful  effects  obtainable  from  thin  films  of  solid,  fluid,  and  gaseous  bodies, 
or  the  action  of  crystallized  bodies  on  polarized  light,  they  do  altogether 
impress  the  reasoning  faculties  with  a  conviction  that  a  vibrating  motion 
accompanies  the  production  of  all  light,  which  can  only  be  propagated  by 
the  communication  of  these  vibrations  or  tremblings  to  a  medium,  itself  as 
subtile,  rare,  and  exquisite  as  the  delicate  mechanism  that  sets  it  in  motion. 

What  is  the  real  nature  of  the  medium  called  ‘•ether”  can  only  be  con¬ 
jectural,  or  perhaps  attempted  to  be  explained  by  elaborate  mathematical 
reasoning. 

Lately  the  scientific  world  has  been  excited  with  the  hope  that  the  long- 
desired  evidence  of  the  absolute  existence  of  a  more  “subtile  medium  than 
air”  was  at  last  established  by  the  very  original  experiments  of  William 
Crookes,  Esq.,  F.R.S.,  with  a  curious  and  remarkable  instrument  which  he 
has  invented  and  called  the  Radiometer. 

Originality  is  defined  to  be  the  form  of  producing  new  thoughts,  or  uncom¬ 
mon  combinations  of  thoughts  ;  it  is  a  very  rare  gift,  and  was  undoubtedly 
enjoyed  by  Davy  and  Faraday,  and  is  abundantly  apparent  in  the  exhaus¬ 
tive  papers  read  by  Mr.  Crookes  before  the  Royal  Society  during  1873- 
4- 5-6-7.  These  p  ipers,  commencing  with  the  description  of  the  various  steps 
which  led  to  the  construction  of  the  radiometer,  and  detailing  the  laborious 
and  patient  experiments  performed  with  that  apparatus,  are  continued  with 
another  and  equally  ingenious  instrument  constructed  by  the  same  fertile  in¬ 
ventor,  with  the  able  help  of  his  friend  and  assistant,  Mr.  C.  H.  Gimingham, 
and  called  by  Mr.  Crookes  the  Otheoscope  ( wdto ,  I propel?) 

On  Attraction  and  Repulsion  resulting  from  Radiation. 

1.  In  a  paper  “  On  the  Atomic  Weight  of  Thallium,”  presented  to  the  Royal 
Society,  June  18th,  1872,  after  describing  a  balance  with  which  I  was  enabled 
to  perform  weighings  of  apparatus,  &c.,  in  a  vacuum,  I  noted  a  peculiarity  in 
relation  to  the  effect  of  heat  in  diminishing  the  apparent  weight  of  bodies. 

.  .  .  With  the  vacuum  balance  1  carried  out  many  experiments,  but  was 
unable  to  obtain  results  which  were  at  all  concordant  ;  and  it  was  soon  found 
necessary  to  investigate  the  phenomena  with  smaller  and  less  complicated 
apparatus. 

2.  Most  chemical  manuals  warn  beginners  against  the  errors  occasioned  by 


6 


ON  LIGHT. 


weighing  substances  while  hot  ;  and  up  to  a  moderately  high  degree  of  ex¬ 
haustion  I  am  prepared  to  find  a  piece  of  glass  apparatus,  when  hot.  apparently 
lighter  than  the  weight  which  should  balance  it  were  the  whole  system  at  the 
same  temperature.  But  instead  of  the  interfering  causes  diminishing  as  the 
rarefaction  proceeded,  they  seemed  rather  to  increase,  or,  at  all  events,  to  be¬ 
come  irregular  in  their  action — sometimes  appearing  to  oppose,  and  at  others 
to  supplement  the  force  of  gravity.  In  such  a  vacuum  as  a  good  air-pump 
would  produce,  the  actions  of  the  ascending  current  of  air  and  of  the  adhering 
film,  it  might  be  presumed,  should  cease  to  exert  an  influence  ;  and  1  could 
think  of  no  other  disturbing  cause  except  the  lengthening  of  the  beam,  owing 
to  the  heat  radiating  from  the  apparatus  below  it.  An  increase  in  the  length 
of  the  beam  should  make  a  mass  suspended  at  its  extremity  appear  heavier ; 
but  whilst  I  frequently  noticed  an  action  which  might  be  a  clue  to  this  cause, 
I  occasionally  obtained  results  which  were  so  anomalous  as  to  convince  me 
that  some  cause  which  I  had  not  hitherto  recognized  was  at  work,  and  to  lead 
me  to  hope  that  perhaps  I  might  succeed  in  tracing  a  connection  between  heat 
and  the  force  of  gravity. 

3.  Many  physicists  have  worked  on  the  subject  of  repulsion  by  heat. 

[After  giving  a  brief  resume  of  the  state  of  knowledge  on  this  subject  up  to 

the  time  that  Mr.  Crookes  commenced  his  experiments,  the  author  says  :] 

4.  In  his  “  Elementary  Treatise  on  Heat.”*  Professor  Balfour  Stewart, F.R.S  , 
cites  Bennet’sf  experiment  as  one  of  the  arguments  against  the  Emission,  and 
in  favour  of  the  Undulatory  Theory  of  light  and  heat.  Bearing  in  mind  the 
overwhelming  proofs  we  now  possess  that  the  undulatory  theory  more  nearly 
expresses  the  truth  than  does  the  emission  theory,  it  is  not  likely  that  the 
very  different  results  I  have  succeeded  in  obtaining,  by  the  employment  of 
instruments  of  a  delicacy  unattainable  eighty  years  ago^will  have  any  weight 
in  modifying  the  accepted  theories  of  light  and  heat. 

[Paragraphs  5,  6,  7,  8,  9,  10,  11,  12,  13,  14,  15,  refer  to  the  mention  of  the 
dynamic  action  of  heat,  and  expeiiments  by  various  physicists  and  mathema¬ 
ticians,  viz.,  by  Laplace,11  Libri,b  the  Rev.  Baden  Powell,®  Fresnel, d  Saigey,® 
J.  D.  Forbes, f  also  a  special  paper  by  the  Rev.  Baden  Powell,8  “  On  the 
Repulsive  Power  of  He’t,”  supplemented  by  additional  notes  on  the  same 
subject,  in  1838,  Dr.  Joule,  F.R  S.h  J.  Reynolds  (1871)  constructed  a  little 
instrument  which  would  turn  to  the  hand,  to  a  fire,  or  to  any  source  of  heat. 
Professor  Guthrie,  F.  K.S.,1  distinctly  points  out  a  probable  relation  between 
heat  and  gravity.  He  says  :  “  If  the  aethereal  vibrations  which  are  supposed  to 
constitute  radiant  heat  resemble  the  aerial  vibrations  which  constitute  radiant 
sound,  the  heat  which  all  bodies  possess,  and  which  they  are  all  supposed  to 
radiate  in  exchange,  will  cause  all  bodies  to  be  urged  towards  one  another.”] 

16.  Were  it  such  a  relation  between  heat  and  gravity,  of  which  I  had  been 


*  Oxford,  at  the  Clarendon  Press,  1866,  pp.  161,  352.  t  “  Philosophical  Transactions,  1792,”  p.  81. 

a  “Suppl.  Livr.,”  x.,  p.  75,  a.d.  1799 — 1805. 
b  “  Mem.  Acad.  Torrino,"  18  — 1824. 
c  “Phil.  Trans.,”  p.  485,  1834. 

d  “  Annales  de  Chimie  et  de  Physique,”  vol.  xix.,  pp.  57,  107,  1825. 

e  “  Bulletin  Mathematique,”  tom.  ix.,  pp.  89,  167,  239;  tom.  xi.,  No.  167.  “Bull.  Sci.  Nat.,”  viii., 
p.  287,  1827. 

*  “Trans.  Roy.  Soc.,  Edinburgh,”  vol.  xii.,  p.  429,  1834. 
g  “  Phil.  Trans.,”  p.  485,  1834. 

h  “Chemical  News,”  vol.  vii.,  p.  150,  1863. 

*  “  Proceedings  of  the  Royal  Society,”  vol.  xix.,  p.  33,  1S68. 


ON  LIGHT. 


7 


getting  glimpses,  it  was  evident  that  a  much  more  delicate  apparatus  would 
be  necessary  to  render  it  distinct  ;  and  I  accordingly  commenced  a  series  of 
experiments  with  the  view  of  ascertaining  what  form  of  apparatus  would  be 
most  sensitive  to  the  action  sought.  [  I  lie  nature  and  extent  of  the  series  of 
experiments  may  be  estimated  by  youthful  aspirants  to  scientific  fame  when 
it  is  stated  ihat  long  paragraphs,  from  17  to  73,  are  devoted  by  Mr  Crookes 
to  the  description  of  rejected  arrangements  of  balances  and  an  improved 
Sprengel  pump— a  perfect  method  of  obtaining  a  “chemical  vacuum;”  in 
fact,  the  novel  experiments  necessitated  new  terms.  The  author  remarks  :] 
“  I  shall  call  the  best  vacuum  which  my  air-pump  will  give  an  ‘  air-pump 
vacuum This  is  one  or  two  millimetres  below  the  barometer.  The  ordi¬ 
nary  vacuum  produced  by  the  Sprengel  pump  I  shall  call  a  ‘  Sprengel 
vacuum'—  in  this  the  gauge  is  appreciably  level  with  the  barometer.  A  so- 
called  ‘perfect’  vacuum,  produced  by  potash  and  carbonic  acid,  as  subse¬ 
quently  described,  or  by  similar  means,  I  shall  call  a  '‘chemical  vacuum I 
object  to  the  term  peifect  as  applied  to  any  vacuum  at  present  known,  as  1 
believe  that  where  force  can  travel,  we  are  not  justified  in  assuming  the 
absence  of  matter —  imponderable,  it  may  be,  and  unaffected  by  ordinary  forms 
of  force,  but  none  the  less  matter.” 

[And  now  it  may  be  asked — Has  Mr.  Crookes,  by  the  improvement  of  his 
pumping  arrangement  and  the  delicacy  of  apparatus,  further  developed  the 
idea  sought  to  be  illustrated  in  the  experiments  by  Stewart  and  Tait  already 
referred  to  at  page  3?  Reason  and  analogy  would  seem  to  show  that  as  an 
electric  message  or  telegram  requires  matter  as  a  path  or  medium — such  as  a 
connecting  chain,  or  iron,  or  earth,  or  water  circuit — along  which  the  current 
must  pass  or  circulate,  so  an  electric  light  placed  in  a “ chemi,  al  vacuum ”  throws 
out  its  rays,  which  travel  from  the  inside  of  the  glass  receiver  to  the  exterior. 
As  the  rays  undoubtedly  pass  out  and  are  visible  to  the  spectator,  reason  specu¬ 
lates  upon  the  cause,  and  confidently  asserts  there  must  be  some  connecting- 
link  or  chain,  or  the  undulations  could  not  take  place.  If  there  is  nothing 
left  in  the  receiver,  nothing  can  vibrate  or  undulate :  it  is  a  fundamental  pos¬ 
tulate  that  to  produce  a  wave  of  water,  sound,  or  light,  you  must  have  one  of 
three  media  :  water,  air,  or  the  matter  called  “ether  but  what  the  ether  is 
no  one  can  say  precisely,  unless  it  be  the  “  matter” — the  residual  gas  left  in  a 
so-called  “  perfect  vacuum  ;  ”  and  if  this  be  the  case  on  the  small  scale, analogy 
points  to  space,  and  ventures  to  hint  that  even  this  vast  depth  may  be  filled 
with  the  same  matter,  regarded  as  imponderable,  and  infinitely  subtile  and 
elastic,  but  perhaps  fulfilling  the  conditions  summed  up  by  philosophers  when 
they  speak  of  “ether” 

[With  respect  to  the  balance,  after  trying  brass  wire,  fine-grained  charcoal 
saturated  with  shellac,  mica,  magnesium,  also  gridiron  beams  of  zinc  and  iron, 
or  zinc  and  glass,  or  glass  alone,  the  author  says  :]  “  1  finally  adopted  straw  as 
the  material  for  the  beam,  varying  the  gravitating  masses  or  balls  at  the  end 
as  experience  dictated.  Straw  possesses  many  advantages  :  it  is  exceedingly 
light,  yet  rigid  ;  it  dries  easily  and  evolves  no  vapour  in  a  vacuum  ;  more¬ 
over,  it  is  not  likely  to  introduce  errors  by  altering  in  shape  under  the  influence 
of  the  moderate  degrees  of  temperature  to  which  it  is  subjected  in  these  ex¬ 
periments.”  The  mode  of  supporting  the  beam  of  straw  is  thus  described  : 
The  pointed  half  of  a  small  sharp  needle  is  broken  off  about  half  a  millimetre 
shorter  than  the  internal  diameter  of  the  glass  tube  ;  the  blunt  end  is  then 
ground  very  sharp  on  an  Arkansas  stone.  The  straw,  about  7  in.  long,  having 


8 


ON  LIGHT. 


A,  tube  belonging  to  the  Sprengel  pump  ;*  b,  desiccator  full  of 
glass  beads  moistened  with  sulphuric  acid  :  C,  tube  containing 
the  straw  balance,  with  pith  ends  drawn  out  to  a  contracted  neck 
at  the  end  connected  with  the  pump,  so  as  to  readily  admit  of 
being  sealed  off  if  desired  at  any  stage  of  the  exhaustion  ;  D, 
pump  gauge  ;  E,  the  barometer 


its  gravitating  masses  (or  balls)  at  the  ends,  is 
then  balanced  on  a  knife-edge  so  as  to  let  it  roll 
over  to  a  stable  position  and  to  find  its  centre  ; 
and  the  needle  is  then  run  through  it  at  right 
angles,  at  such  a  distance  above  the  horizontal 
centre  of  the  straw  that  the  centre  of  gravity  is 
a  little  below  the  centre  of  suspension.  The 
beam  being  slipped  into  the  glass  tube  (sealed  at 
one  end),  the  needle  is  supported  very  delicately 
against  the  sides  of  the  glass  by  its  points,  and 
with  the  least  possible  amount  of  friction.  It  is 
best  now  to  exhaust  temporarily,  heating  the  straw 
by  passing  a  spirit  flame  along  the  tube,  so  as  to 
drive  off  moisture.  If — as  is  almost  certain  to 
be  the  case  one  end  becomes  heavier  than  the 
other,  equilibrium  can  be  restored  without  much 
difficulty  bv  holding  the  spirit  flame  for  a  few 
seconds  under  the 'heavier  end',  so  as  to  slightly 

*  For  full  description  of  this  pump  with  diagrams,  see  “  Phil. 

Trans.,”  1873,  vol.  clxiii.,  p.  295. 


ON  LIGHT. 


9 


char  the  straw  or  other  material.  When  in  good  adjustment  and  sufficiently 
sensible,  the  balance  is  ready  for  expeument. 

The  material  with  which  I  form  the  masses  at  the  ends  includes  platinum, 
brass,  silver,  lead,  bismuth,  aluminium,  magnesium,  glass,  selenium,  ivory, 
charcoal  of  various  kinds,  straw,  cork,  and  silk.  With  each  of  these  a  larger 
series  of  experiments  were  tried,  and  the  experience  gained  with  each  was 
turned  to  account  in  making  subsequent  apparatus.  The  most  dtlicate  ap¬ 
paratus  for  general  experiment  is  made  with  a  straw  beam  having  pith  masses 
at  the  end.  The  general  apparatus  is  shown  in  the  annexed  figure. 

The  whole  being  fitted  up  as  here  shown,  and  the  apparatus  being  full  of  air, 
to  begin  with,  I  passed  a  spirit  flame  across  the  lower  part  of  the  tube  at  B 
(Fig.  a),  observing  the  movement  with  a  low  power  micrometer;  the  pith- 
ball  (a  b)  descended  slightly,  and  then  immediately  rose  to  considerably  above 
its  original  position.  It  seemed  as  if  the  true  action  of  the  heat  was  one  of 
attraction,  instantly  overcome  by  ascending  currents  of  air.  A  hot  metal  or 
glass  rod,  and  a  tube  of  hot  water  applied  beneath  the  pith-ball  at  B,  pro¬ 
duced  the  same  effect  as  the  flame  ;  when  applied  above  at  A,  they  produced 
a  slight  rising  of  the  ball.  The  same  effects  take  place  when  the  hot  body  is 


applied  to  the  other  end  ot  the  balanced  beam.  In  these  cases  air  currents 
are  sufficient  to  explain  the  rising  of  the  bad  under  the  influence  of  heat. 

In  order  to  apply  the  heat  in  a  more  regular  manner,  a  thermometer  was 
inserted  in  a  glass  tube,  having  at  its  extremity  a  glass  bulb  about  i|  in.  in 
diameter;  it  was  filled  with  water  and  then  sealed  up  (Fig.  b).  This  was 
arranged  on  a  revolving  stand,  so  that  bv  means  of  a  cord  I  could  bring  it  to 
the  desired  position  without  moving  the  eye  from  the  micrometer.  The  water 
was  kept  heated  to  70°  C,  the  temperature  of  the  laboratory  being  about  1 50  C. 

The  pump  was  now  set  to  work  and  the  hot  ball  (Fig.  B)  placed  beneath  the 
pith-ball  at  B  (Fig.  a)  ;  the  ball  rose  rapidly  when  the  barometer  was  767 
millims  and  the  gauge  at  zero.  When  the  gauge  was  147  millims  below  the 
barometer  the  experiment  was  tried  again  ;  a  similar  result,  only  more  feeble, 
was  obtained. 

As  the  vacuum  was  increased,  the  effect  of  the  hot  ball  on  the  pi'h-ball 
diminished,  until  when  the  gauge  was  about  12  millims  below  the  barometer, 
the  action  of  the  hot  body  was  scarcely  noticeable  ;  at  10  it  was  still  less,  and 
at  7  millims  between  the  barometer  and  the  gauge,  the  pith-ball  did  not  move 
in  an  appreciable  degree. 

Here  many  experimentalists  might  have  stopped,  but,  to  show  my  reader 
how  persevering  and  industrious  a  discoverer  must  be,  the  details  (though 
abbreviated)  of  these  experiments  are  continued. 

Mr.  Crookes  continued  the  exhaustion,  when,  strange  to  say,  the  pith-ball 
B  rose  on  the  application  of  the  heated  ball.  With  the  gauge  3  millims  below 
the  barometer,  the  ascension  of  the  pith  when  a  hot  body  was  placed  beneath 


IO 


ON  LIGHT 


it  was  equal  to  what  it  had  been  in  air  of  ordinary  density ;  whilst  with  the 
gauge  and  barometer  level  its  upward  movements  were  not  only  sharper  than 
they  had  been  in  air,  but  they  took  place  under  the  influence  of  far  less  heat 
— the  finger,  for  example,  instantly  repelling  the  ball  to  its  fullest  extent.  All 


A  B,  tube  containing  straw  heater  with  pith-bait  terminals ;  at  B,  two  platinum  wires  inserted  to  con¬ 
nect  with  coil  ;  at  A ,  tube  contracted  to  allow  apparatus  to  be  sealed  off ;  c,  that  portion  of  the  tube 
containing  a  copper  boat  filled  with  freshly-cast  sticks  of  caustic  potash  ;  l>,  tube  bent  as  shown,  nearly 
full  of  strong  sulphuric  acid,  which  has  been  previously  boiled  for  some  minutes,  and  then  allowed  to 
cool  in  a  vacuum  ;  e,  a  mercury  joint  connecting  the  apparatus  with  the  Sprengel’s  pump. 


these  results  were  verified  by  reversing  the  experiment  and  allowing  air  to  re¬ 
enter. 

The  effect  of  cold  on  the  balance  pith-balls  was  tried  with  a  lump  of  ice. 

With  the  balance  full  of  air,  a  faint  upward  motion  was  observed  ;  at  7 
millims  below  the  vacuum  it  was  absolutely  inert ;  at  last,  when  by  exhaustion 
the  gauge  and  barometer  were  level,  the  attraction  of  the  ice,  whether  applied 
above  or  below,  was  very  marked,  being  exactly  opposite  but  equal  to  the  action 
of  the  bulb  of  water. 

Having  observed  that  the  repulsive  action  of  the  hot  ball  became  greater 


ON  LIGHT. 


1 1 


as  the  vacuum  was  increased,  Mr.  Crookes  thought  it  of  interest  to  see  what 
would  take  place  in  a  vacuum  so  nearly  perfect  that  it  would  not  carry  a  cur¬ 
rent  from  a  Ruhmkorff’s  coil  ;  he  according  fitted  up  the  apparatus  shewn  at 
Fig.  C,  in  which  the  reader  is  shown  how  a  chemical  vacuum  can  be  obtained 
by  a  method  first  devised  by  Dr.  Andrews.* 

At  the  upper  part  of  the  tube  D  is  a  stopper  fitted  into  a  funnel  joint,  and 
capable  of  being  replaced  (as  shown  in  Fig.  c)  by  a  tube,  through  which 
carbonic  acid  could  be  passed  when  desirable. 

The  carbonic  acid  was  prepared  bv  the  action  of  hydro-chloric  acid  on 
marble  ;  when  not  being  passed  into  the  exhausted  tube,  the  gas  was  kept 
bubbling  through  mercury,  when  a  tube  could  be  collected  from  time  to  time 
(as  shown  in  figure)  to  test  with  potash. 

It  was  found  necessary  to  keep  the  evolution  going  on  pretty  briskly,  to 
prevent  air  diffusing  in. 

The  joints  were  made  of  double  caoutchouc  tubing,  the  smaller  one  tightly 
wired  on  and  coated  with  glycerine  before  the  larger  tube  was  slipped  over 
it.  The  whole  was  then  tightly  bound  with  wire. 

To  prevent  air  creeping  down  between  the  mercury  and  the  glass,  glycerine 
was  poured  over  all  the  mercury  joints  except  the  one  at  the  top  of  the  mercury 
fall-tube,  which  was  kept  for  oil  of  vitriol,  with  which  the  Sprengel  pump  was 
lubricated  from  time  to  time. 

Mr.  Crookes  notes  that  when  the  pump  is  working  in  a  very  good  vacuum, 
the  friction  of  the  falling  mercury  produces  a  very  beautiful  effect  in  the  dark. 
Brilliant  points  of  light  flash  about  wherever  the  mercury  drops  are  splashed 
from  side  to  side,  and  the  pump  is  frequently  illuminated  with  a  phosphores¬ 
cent  glow,  filling  all  the  tubes. 

The  air  being  removed  from  the  apparatus  as  perfectly  as  the  Sprengel 
pump  would  effect  it,  carbonic  acid  was  let  into  the  tube  by  cautiously  open¬ 
ing  the  tap  h  in  Fig.  C.  Exhaustion  was  again  effected,  and  carbonic  acid 
passed  in  a  second  time  ;  this  was  then  pumped  out,  and  the  apparatus  was 
filled  a  third  time.  This  alternate  filling  with  carbonic  acid  and  exhaustion 
was  continued  until  the  gas  collected  at  the  bottom  ol  the  mercury  fall-tube  of 
the  pump  was  entirely  absorbed  by  potash.  When  this  was  found  to  be  the 
case,  the  exhaustion  was  allowed  to  proceed  to  the  highest  possible  point. 
The  pump  was  then  stopped.  An  induction  current  now  being  passed  between 
the  wires  at  the  end  15,  showed  the  usual  white  light  of  a  carbonic  acid  vacuum 
(a  trace  of  red  shows  atmospheric  nitrogen).  The  sticks  of  potash  in  the 
copper  boat  in  C  were  then  heated  to  incipient  fusion,  and  the  whole  was 
allowed  to  cool  for  some  hours.  The  tube  was  then  sealed  off  by  applying  a 
spirit-lamp  to  the  contracted  part,  and  the  potash  was  then  heated  again,  and 
the  whole  was  set  aside  to  give  the  potash  time  to  absorb  the  residual  carbonic 
acid. 

The  youthful  reader  is  particularly  referred  to  the  above  as  a  model  or  per¬ 
fect  example  of  thoughtful,  elaborate,  and  laborious  preparation  of  apparatus 
Tor  other  purposes  of  research. 

A  point  was  reached  when  the  chemical  vacuum  no  longer  permitted  the 
current  from  an  induction  coil  to  pass,  and  the  delicacy  of  the  straw  and  pith- 
balances  was  so  exquisite,  that  when  the  balance-tube  was  supported  on  a 
stand,  and  the  face  of  a  bismuth-antimony  (A,  Fig.  2,  page  3)  thermo  pile 


*  “Phil.  Mag."  February,  1852. 


12 


ON  LIGHT. 


placed  beneath  one  of  the  pith-balls,  it  was  repelled  by  connecting  the  thermo 
pile  with  a  single  coil  battery  because  heat  was  produced  ;  and  on  reversing 
the  current,  the  pith-ball  was  attracted  because  cold  was  produced. 

The  rays  of  the  sun  allowed  to  shine  on  the  terminal  pith-ball  of  one  of 
these  delicate  balances  (in  vacuo )  repel  it  strongly.  If  concentrated  by  a 
lens,  the  focal  point  beats  the  ball  away,  as  if  it  was  struck  with  a  material 
agent.  If  the  sunlight  be  filtered  through  coloured  glasses  before  concen¬ 
trating  them  on  the  pith- ball,  the  action  is  slightly  diminished.  Passing  the 
light  through  two  very  clear  plates  of  alum  with  parallel  sides,  and  having 
an  aggregate  thickness  of  8  millimetres,  had  but  little  action.  On  placing  the 
pith-ball  in  the  various  colours  of  the  spectrum,  the  repellent  action  in  the 
ultra-violet  rays  was  slight ;  the  effect  increased  from  the  violet  to  the  red. 

The  maximum  action  was  in  the  extreme  visible  red,  and  it  gradually  faded 
away  as  the  invisible  rays  beyond  the  red  were  used.  An  appreciable  action 
of  repulsion  was,  however,  observed  a  full  half-spectrum  length  below  the 
least  refrangible  visible  rays.  The  plate  of  alum  interposed  in  the  path  of 
the  rays  cut  off  a  small  portion  only  of  their  action.  The  limits  of  this  work 
forbid  the  description  of  the  numerous  experiments,  which  were  constantly 
varied  by  the  genius  of  the  author,  and  two  important  laws  were  eliminated. 

I.  When  the  ball  is  in  air  of  ordinary  density. 

A.  If  the  mass  is  colder  than  the  ball  it  repels  the  ball. 

B  If  the  mass  is  hotter  than  the  ball  it  attracts  the  ball. 

1 1.  When  the  ball  is  in  a  vacuum. 

A.  If  the  mass  is  colder  than  the  ball  it  attracts  the  ball. 

B.  If  the  mass  is  hotter  than  the  ball  it  repels  the  ball. 

Mr.  Crookes  summed  up  the  results  of  all  these  experiments,  and  whilst 
apparently  rejecting  the  notion  that  the  movements  of  the  ball  were  caused 
by  currents  of  air,  was  inclined  to  believe  that  the  effects  were  due  to  the 
repulsive  action  of  heat ;  although  the  force,  as  he  remarks,  is  clearly  not 
gravity  solely,  as  we  know  it  is  attraction  developed  from  chemical  activity, 
and  connecting  tnat  greatest  and  most  mysterious  of  all  natural  forces,  action 
at  a  distance,  with  the  more  intelligible  acts  of  matter.  In  the  radiant  mole¬ 
cular  energy  of  solar  masses  may  at  last  be  found  that  “  agent  acting  con¬ 
stantly  according  to  certain  laws,”  which  Newton  held  to  be  the  cause  of 
gravity. 

In  other  papers  read  by  Mr.  Crookes  before  the  Royal  Society, “On  Repul¬ 
sion  resulting  from  Radiation”  (1875,  1876),  still  more  elaborate  experiments 
are  recorded.  The  balance-tube  and  pith-ball  apparatus  was  gradually  im¬ 
proved  until  it  took  the  form  now  generally  known,  and  called  by  its  inventor 
the  Radiometer.  The  apparatus  is  shown  in  Fig.  D. 

It  consists  of  four  arms  of  very  fine  glass,  passing  horizontally  through 
pieces  of  pith  (b),  and  afterwards  bent  twice  at  right  angles,  as  shown  in  the 
tigure.  Through  the  centre  of  the  pieces  of  pith  (b)  is  passed  vertically  the 
point  of  a  very  fine  sewing-needle  (a),  which  rests  in  a  glass  cup  (c)  blown  on 
to  the  end  of  the  glass  tube  E.  At  the  end  of  each  glass  arm  is  fastened  a 
thin  disc  of  pith,*  white  on  one  side  and  lampblacked  on  the  other,  the  black 
surfaces  of  all  the  d  scs  facing  the  same  way.  The  whole  is  enclosed  in  a 
glass  bulb  blown  on  to  the  end  of  a  wide  tube.  F  is  a  piece  of  cement  to  keep 


*  The  vanes  of  radiometers  have  also  been  formed  of  metal  cones,  and  of  cups  and  cones  of  plain 
mica,  roasted  mica,  pith,  paper,  &c. ;  flies’  and  butterflies’  wings,  talc,  selenite,  thin  glass,  iron,  cork ; 
pith  preferred. 


ON  LIGHT. 


13 


the  support  (e)  in  its  place.  G  is  the  tube  containing  cocoa-nut  charcoal ;  the 
other  end  is  sealed  on  to  the  Sprengel’s  pump. 

The  exhaustion  is  effected  as  already  described  (p.  8),  and  the  apparatus 
is  then  sealed  oft,  with  the  charcoal  tube  still  attached  to  it  Ultimately  when 
all  the  residual  gas  has  been  absorbed  by  the  charcoal,*  a  flame  is  applied  to 
the  contracted  part  of  the  tube  at  B,  and  the  charcoal  tube  is  disconnected. 

Mr.  Crookes  says  :  “  I  have  proposed  lor  this  instrument  the  name  of  the 
Radiometer ,  as  it  serves  to  measure  the  amount  of  radiation  falling  upon  it  by 
the  velocity  with  which  it  re¬ 
volves.  It  may  also  be  called 
the  Light  Mill.  The  rapidity 
of  revolution  is  directly  propor¬ 
tional  to  the  intensity  of  the 
incident  rays.” 

As  soon  as  the  radiometer 
was  seen  to  revolve,  it  was 
apparent  that  the  stronger  the 
light  the  more  rapid  the  move¬ 
ment,  and  the  revolution  by 
the  action  of  rays  will  remind 
the  reader  of  Faraday's  delight 
when  he  caused  the  wire  carry¬ 
ing  a  current  of  electricity  to 
rotate  around  a  magnet, and  the 
magnet  around  the  wire  ;  so 
Mr.  Crookes  not  only  obtained 
the  rotation  of  the  vanes  inside 
the  glass,  but  the  revolution  of 
the  glass  case  of  a  radiometer 
—  showinghow  exhaustive  were 
all  his  experiments  that  gradu¬ 
ally  led  to  the  enunciation  of 
the  theory  of  the  apparatus, 
which  can  be  conveniently  and 
accurately  used  as  a  photo¬ 
meter. 

Thoughtful  observers  were  continually  asking— Is  the  effect  due  to  heat  or 
light?  Mr.  Crookes  replies,  “I  cannot  answer  this  question.  The  terms 
heat  and  light  are  not  definite  enough.  The  physicist  has  no  test  for  light  in¬ 
dependent  of  heat.  Light  and  colour  are  physiological  accidents,  due  to  the 
fact  that  a  small  portion  near  the  middle  of  the  spectrum  happens  to  be  ca¬ 
pable  of  affecting  the  retina  of  the  eye.  There  is  no  real  distinction  between 
heat  and  light :  all  we  can  take  account  of  is  difference  of  wave-length  ;  and 
all  we  can  see  in  the  spectrum  is  one  continuous  series  of  vibrations,  larger  at 
the  red  end  than  at  the  violet  end,  but  extending  in  an  unbroken  series  for  an 
unknown  distance  on  each  side.  I  say  unknown,  for  it  is  probable  that  the 
whole  spectrum  as  we  know  it  is  limited  by  the  imperfect  transparency  of  the 
atmosphere,  or  of  the  refracting  medium  for  the  extreme  ultra-red  and  ultra¬ 
violet  rays.  _ 


Fig.  d. 


Dr.  Angus  Smith's  and  Professor  Dewar  s  method  of  absorbing  the  residual  gas  by  means  of  cocoa- 

nut-shell  charcoal. 


*4 


ON  LIGHT. 


Take  a  ray  of  the  spectrum  of  a  definite  wave-length  (the  line  B,  for  instance), 
and  allow  it  to  fall  upon  a  thermometer  :  the  mercury  rises,  showing  the  action 
of  heat ;  concentrate  it  on  the  hand  by  a  lens,  it  raises  a  blister  accompanied 
with  pain  ;  let  it  fall  on  a  bismuth  and  antimony  couple,  the  galvanometer  is 
deflected  ;  and  this  action  we  also  call  one  of  heat :  let  the  ray  fall  upon  the 
eye,  and  it  produces  the  sensation  of  light  and  colour;  let  it  fall  on  a  collodion 
plate  prepared  in  a  particular  manner,  and  it  gives  a  permanent  image, 
showing  that  it  can  cause  chemical  action;  lastly,  throw  the  ray  on  a  portion 
of  matter  free  to  move  in  a  vacuum,  and  it  makes  itself  evident  as  motion. 
Now,  these  actions  of  heat ,  light ,  colour,  chemical  action ,  and  motion,  are 
inseparable  attributes  of  the  ray  of  that  particular  wave-length  ;  and  to  con¬ 
sider  that  there  can  be  a  splitting  up  of  this  ray  into  two  or  more  rays  of  the 
same  refrangibilitv,  one  having  the  property  of  light,  the  other  of  heat,  &c.,  is 
to  my  mind  an  absurdity.” 

Finally  Mr.  Crookes  sums  up  all  by  saying  that  there  can  be  no  reasonable 
doubt  that  the  presence  of  residual  gas*  is  the  cause  of  the  movement  of  the 
radiometer.  The  explanation,  as  given  by  Mr.  Johnstone  Stoney,  appears  to 
me  the  most  probable,  and  having  stood  almost  every  experimental  test  to 
which  I  have  submitted  it,  I  may  assume  for  the  present  that  it  expresses  the 
truth.  According  to  this  the  repulsion  is  due  to  the  internal  movement  of 
the  molecules  of  the  residual  gas.  When  the  mean  length  of  path  between 
successive  collisions  of  the  molecules  is  small,  compared  with  the  dimensions 
of  the  vessel,  the  molecules  rebounding  from  the  heated  surface,  and  therefore 
moving  with  an  extra  velocity,  help  to  keep  back  the  more  slowly-moving 
molecules  which  are  advancing  towards  the  heated  surface  ;  it  thus  happens 
that  though  the  individual  kicks  against  the  heated  surface  are  increased  in 
strength  in  consequence  of  the  heating,  yet  the  number  of  molecules  struck  is 
diminished  in  the  same  proportion,  so  that  there  is  equilibrium  on  the  two  sides 
of  the  disc,  even  though  the  temperature  of  the  faces  is  unequal.  But  when  the 
exhaustion  is  carried  to  so  high  a  point  that  the  molecules  are  sufficiently  few, 
and  the  mean  length  of  path  between  their  successive  collisions  is  comparable 
with  the  dimensions  of  the  vessel,  the  swiftly-moving  rebounding  molecules 
spend  their  force,  in  part  or  in  whole,  on  the  sides  of  the  vessel  ;  and  the 
unusual  crowding,  more  slowly-moving  molecules  are  not  kept  back  as  before, 
so  that  the  number  which  strike  the  warmer  face  approaches  to,  and  in  the 
limit  equals,  the  number  which  strike  the  back  cooler  face  ;  and  as  the  in¬ 
dividual  impacts  are  stronger  on  the  warmer  than  on  the  cooler  face,  pressure 
is  produced,  causing  the  warmer  face  to  retreat. 

Application  of  the  Direct  Rays  of  the  Sun  as  a  Motive  Power. 

In  April  of  this  year  (1877),  another  paper  was  read  before  the  Royal 
Society  by  William  Crookes,  Esq.,  F.R.S.,  “On  Repulsion  resulting  from 
Radiation.  ’ 

Alluding  to  a  previous  paper  containing  an  account  of  certain  radiometers 
he  had  made  with  the  object  of  putting  to  experimental  proof  the“  Molecular 
Pressure  ”  theory  of  the  repulsion  resulting  from  radiation,  the  author  says  : 

“  Continuing  these  researches,  I  have  constructed  other  instruments,  in 


*  It  is  a  question  whether  the  residual  gas  in  the  apparatus,  when  so  highly  attenuated  as  to  have 
lost  the  greater  part  of  its  viscosity,  and  to  be  capable  of  acquiring  molecular  movement  palpable 
enough  to  overcome  the  inertia  of  a  plate  of  metal,  should  not  be  considered  to  have  got  beyond  the 
gaseous  state ,  and  to  have  assumed  a  fourth  state  of  matter  in  which  its  properties  are  as  far  removed 
from  those  of  a  gas  as  this  is  from  a  liquid. 


ON  LIGHT. 


1 5 


which  a  movable  fly  is  caused  to  rotate  by  the  molecular  pressure  generated 
on  fixed  parts  of  the  apparatus. 

“  In  the  radiometer,  the  surface  which  produces  the  molecular  disturbance 
is  mounted  on  a  fly,  and  is  driven  backwards  by  the  excess  of  pressure  be¬ 
tween  it  and  the  sides  of  the  containing  vessel.  Regarding  the  radiometer  as 
a  heat  engine,  it  is  seen  to  be  imperfect  in  many  respects.  The  black  or 
driving  surface,  corresponding  to  the  heater  of  the  engine,  being  also  part  of 
the  moving  fly,  is  restricted  as  to  weight,  material,  and  area  of  surface.  It 
must  be  of  the  lightest  possible  construction,  or  friction  wi  1  greatly  interfere 
with  its  movement  ;  it  must  not  expose  much  surface,  or  it  will  be  too  heavy; 
and  it  must  be  a  very  bad  conductor  of  heat,  so  as  to  retain  the  excess  of 
pressure  on  one  side.  Again,  the  part  corresponding  to  the  cooler  of  the 
engine  (the  side  of  the  glass  bulb)  admits  of  but  little  modification.  It  must 
almost  necessar.ly  be  of  glass,  by  no  means  the  best  material  for  the  purpose; 
it  is  obliged  to  be  of  one  particular  shape,  and  it  cannot  be  brought  very  near 
the  driving  surface.  A  perfect  instrument  would  be  one  in  which  the  heater 
was  stationary  ;  it  might  then  be  of  the  most  suitable  material,  of  sufficient 
area  of  surface,  and  of  the  most  efficient  shape,  irrespective  of  weight.  The 
cooler  should  be  the  part  that  moves  ;  it  should  be  as  close  as  possible  to  the 
heater,  and  of  the  best  size,  shape,  and  weight  for  utilizing  the  force  impinging 
on  it.  By  having  the  driving  surface  of  large  size,  and  making  it  of  a  good 
conductor  of  heat,  such  as  silver,  gold,  or  copper,  a  very  faint  amount  of  in¬ 
cident  radiation  suffices  to  produce  motion.  The  black  surface  acts  as  if  a 
molecular*  wind  were  blowing  from  it,  principally  in  a  direction  normal  to  the 
surface.  This  wind  blows  away  whatever  easily  movable  body  happens  to  be 
in  front  of  it,  irrespective  of  colour,  shape,  or  material ;  and  in  its  capability 
of  deflection  from  one  surface  to  another,  its  arrest  by  solid  bodies,  and  its 
tangential  action,  it  behaves  in  most  respects  like  an  actual  wind. 

Whilst  the  radiometer  admits  of  but  few  modifications,  such  an  instrument 
as  the  one  here  sketched  out  is  capable  of  an  almost  endless  variety  of  forms ; 
and  as  it  is  essentially  different  in  its  construction  and  mode  of  action  to  the 
radiometer,  Mr.  Crookes  proposes  to  identify  it  by  a  distinctive  name,  and 
call  it  the  Otheoscope  1  propel) 

The  glass  bulb  is  an  essential  portion  of  the  machinery  of  the  radiometer, 
without  which  the  fly  would  not  move  ;  but  in  the  otheoscope  the  glass  vessel 
simply  acts  as  a  preserver  of  the  requisite  amount  of  rarefaction.  Carry  a 
radiometer  to  a  point  in  space  where  the  atmospheric  pressure  is  equal  to, 
say,  one  millimetre  of  mercury,  and  remove  the  glass  bulb,  the  fly  will  not 
move,  however  strong  the  incident  radiation.  But  place  the  otheoscope  in 
the  same  condition,  and  it  will  move  as  well  without  the  case  as  with  it.  It 
would  be  possible,  therefore,  to  construct  an  otheoscope  in  which  no  rarefaction 
or  containing  vessel  was  necessary,  but  in  which  motion  would  take  place  in 
air  at  the  normal  density.  Since*  writing  this,  Mr.  Crookes  has  constructed 
such  an  instrument,  and  the  movement  takes  place  in  the  way  he  had 
anticipated  :  should  it  be  possible  hereafter  to  apply  the  direct  heat  of  the 
sun  as  a  motive  power,  instead  of  indirectly  by  coal,  which  miy  be  regarded 
as  a  specie*  of  condensed  sunbeam,  then  a  new  era  will  dawn  upon  the 
mechanical  world,  who  may  hereafter  erect  in  gratitude  and  respect  statues  to 


*  Molecular ,  not  molar.  There  is  no  wind  in  the  sense  of  an  actual  transference  of  air  from  one  place 
to  another.  I'his  molecular  movement  may  be  compared  to  the  movement  of  the  gases  when  water  is 
decomposed  by  an  electric  curtent.  In  the  water  connecting  the  two  poles  there  is  no  apparent  move¬ 
ment,  although  eight  times  as  mu  :h  matter  is  pasting  one  way  as  the  other. 


i6 


ON  LIGHT. 


another  genius  like  Watt.  The  inventor  describes  six  different  forms  of  the 
otheoscope. 

1.  Otheoscope. — A  four-armed  fly,  carrying  four  vanes  of  thin  clear  mica,  is 
mounted  like  a  radiometer  in  an  exhausted  glass  bulb.  At  one  side  of  the 
bulb  a  plate  of  mica  blacked  on  one  side  is  fastened  in  a  vertical  plane,  in 
such  a  position  that  each  clear  vane  in  rotating  shall  pass  the  plate,  leaving 
a  space  between  of  about  a  millimetre.  If  a  candle  is  brought  near,  and  by 
means  of  a  shade  the  light  is  allowed  to  fall  only  on  the  clear  vanes,  no  motion 
is  produced  ;  but  if  the  light  shines  on  the  black  plate,  the  fly  instantly  rotates 
as  if  a  wind  were  issuing  from  this  surface,  and  keeps  on  moving  as  long  as 
the  light  is  near. 

2.  A  four-armed  fly  carries  roasted  mica  vanes,  and  is  mounted  in  an 
exhausted  glass  bulb  like  a  radiometer.  Fixed  to  the  side  of  the  bulb  are 
three  plates  of  clear  mica,  equidistant  from  each  other  in  a  vertical  plane, 
but  oblique  to  the  axis.  A  candle  brought  near  the  fixed  plates  generates 
molecular  pressure,  which  falling  obliquely  on  the  fly  causes  it  to  rotate. 

3.  A  large  horizontal  disc,  revolving  by  the  molecular  disiurbance  on  the 
surface  of  inclined  metallic  vanes,  which  are  blacked  on  both  sides  in  order 
to  absorb  the  maximum  amount  of  radiation. 

4.  1  nclined  aluminium  vanes,  driven  by  the  molecular  disturbance  from  the 
fixed  black  mica  disc  below  blowing  (so  to  speak)  through  them. 

5.  A  large  horizontal  coloured  disc  of  roasted  mica,  driven  by  inclined 
aluminium  vanes  placed  underneath  it. 

6.  A  bright  aluminium  disc  cut  in  segments,  and  each  segment  bound  at  an 
angle,  driven  by  a  similar  one  below  of  lampblacked  silver. 

Starting  with  the  proposition  that  all  sources  of  light  and  luminous  bodies, 
like  musical  instruments,  must  first  vibrate,  it  is  not  difficult  to  understand 
by  analogy  how  these  vibrations  may  travel  at  the  rate  of  186,600  miles  per 
second,  in  straight  lines,  called  rays. 


Fig.  3. 

a.  tuning-fork  struck  on  the  leaden  cone  is,  capped  with  leather,  and  applied  to  the  end  of  the  rod  c, 
whilst  the  other  end  is  held  against  the  sounding-board  D. 


A  tuning-fork  emitting  sound  might  by  analogy  represent  a  source  of  light 
like  the  sun,  whilst  along  rod  communicating  with  it  would  stand  in  the  place 
of  the  theoretical  ether,  propagating  the  undulations  from  the  sun  through  a 
space  of  92,000,000  and  60,000  miles ;  and  if  the  other  end  of  the  rod  com¬ 
municates  with  the  sounding-board  of  a  guitar,  the  audible  sound  obtained 
might  compare  with  the  light  falling  on  the  earth  and  becoming  apparent  by 
radiation. 


ON  LIGHT. 


17 


The  conversion  of  a  continued  series  of  mechanical  impulses  into  waves  is 
beautifully  shown  by  taking  hold  of  the  end  of  a  long  vulcanized  india  rubber 
tube  filled  with  sand,  and  having  attached  one  end  to  the  ceiling  or  other  con¬ 
venient  place,  it  is  easy  by  a  jerk  to  produce  the  appearance  of  a  wave,  which 
travels  distinctly  from  the  hand  to  the  ceiling ;  at  the  same  time  it  demonstrates 
the  progressive  nature  of  the  wave  or  undulation,  and  as  the  portion  held 
by  the  operator  cannot  move  from  his  hand  to  the  ceiling,  it  shows  how  the 
eye  is  deceived  whilst  looking  at  the  motion  of  waves  of  water.  Every  wave 
in  water  is  propagated  by  the  rising  and  falling  of  that  which  has  preceded 
it,  and  not  because  the  volume  of  water  representing  the  wave  travels  bodily 
from  the  spot  where  it  is  first  noticed  to  the  shore  where  it  breaks. 


FlG.  4. —  The  Vulcanized  Tube  attached  to  the  ceiling ,  and  thrown 
into  undulations  or  waves  by  the  hand  of  the  operator. 

Dr.  Tyndall  has  shown,  by  a  modification  of  Dr.  Young’s  experiments  with 
vibrating  strings  upon  which  light  is  thrown,  a  number  of  very  beautiful 
effects.  A  silvered  cord  attached  to  the  iron  arm  of  a  curved  spring  band,  one 
end  of  which  is  made  to  vibrate  by  an  electro-magnet,  displays  the  divisions 
of  the  cords  into  wave-like  figures  most  perfectly  when  the  cord  is  illuminated 
by  the  lime  or,  better  still,  the  electric  light.  (Tigs.  5  and  6,  p.  7.) 

Using  the  brilliant  light  as  before,  a  still  more  perfect  and  admirable  experi¬ 
ment  may  be  conducted  by  attaching  one  end  of  a  bright  silvered  chain  to  a 
hook  screwed  into  a  vertical  whirling  table,  and  the  other  to  a  proper  stand.  The 
chain  being  horizontal  and  the  wheel  vertical,  it  may  be  swung  into  one  long 
wave,  or,  by  a  still  more  rapid  rotation,  can  be  divided  into  three,  four,  or  more. 
The  links  of  the  chain  flash  in  the  light,  and  produce  the  most  pleasing  effects. 

It  must  be  remembered  that  if  cords,  chains,  water,  air,  &c.,  can  assume  a 
wave-like  motion,  the  wonderful  tension  and  elasticity  of  the  hypothetical  ether 


i8 


V  ' 

ON  LIGHT. 


Fig.  6. — The  Silvered  Cham  and  Electric  Light. 


SOURCES  OF  LIGHT. 


*9 


wf'uld  permit  the  latter  to  adapt  itself  to  the  most  complicated  movements 
almost  with  the  rapidity  of  thought.  The  very  spiral,  spindle-like,  or  cork¬ 
screw  motion  observable  in  the  chain  and  cord  affords  a  good  idea  of  the 
mechanism  of  the  propagadon  of  light,  as  the  movement  of  each  molecule  of 
ether  is  always  perpendicular  to  the  path  of  the  ray  or  wave  of  light.  It  can 
easily  be  conceived  that  vibration  of  ether  or  light-waves  must  affect  even 
material  substances,  whether  endowed  with  life  or  not.  Thus  it  is  claimed, 
by  General  A.  J.  Pleasonton,  U.S.A.,  that  remarkable  cures  have  been  effected 
in  cases  of  nervous  disease  (when  the  voltaic  shock  has  failed)  by  merely 
exposing  the  part  affected  to  the  rays  of  the  sun  passed  through  blue  glass. 
Mr.  Willoughby  Smith  has  shown  that  the  electrical  conductivity  of  the 
element  selenium  is  affected  by  exposure  to  light  ;  and  it  was  while  in  charge 
of  the  electrical  department  of  the  laying  of  the  cable  from  Valentia  to 
Hearts  Content,  1866,  and  using  the  high  resistance  of  selenium,  that  Mr. 
Smith  noticed  that  the  deflections  of  the  needle  varied  according  to  the 
intensity  of  light  falling  on  the  selenium,  thus  explaining  the  cause  of  that 
element  not  being  constant  as  a  resistance  medium.  Mr.  Smith  says,  during 
the  laying  of  the  1873  and  1874  Atlantic  cables, ‘T  have  with  success  adopted 
selenium  bars  protected  from  the  action  of  light.” 

The  astonishing  rapidity  of  the  periodic  movements  of  the  non-gravitating 
molecules  of  ether  becomes  apparent,  when  it  is  stated  that  to  produce  white 
light  fivehundred  millionsof  millionsof  vibrations  of  the  ether,  1,000,000,000,000 
X  500  must  occur  in  every  second  of  time. 

Or,  taking  the  coloured  rays  at  the  extremities  of  the  solar  spectrum,  viz., 
the  red  ray  and  the  violet,  the  former  demands  the  recurrence  of  four  hundred 
and  fifty-eight  millions  of  millions,  1,000,000,000,000x458;  and  the  latter, 
the  violet,  a  still  larger  number,  and  greater  rapidity  of  vibration,  six  hundred 
and  ninety-nine  millions  of  millions,  1,000,000,000,000x699,  per  second. 

The  coloured  rays  of  light  are  supposed,  according  to  the  undulatory  theory, 
to  be  distinguished  from  each  by  the  lengths  of  the  different  waves,  just  as 
the  sound  of  a  stringed  instrument  may  vary  according  to  the  diameter  and 
thickness  of  the  strings.  A  tightly-stretched  thin  cord  vibrating  would  be 
the  parallel  to  violet  light.  It  is  an  axiom  that  “  The  rapidity  of  vibration 
is  inversely  proportional  to  the  length  and  diameter  of  the  string,  and  pro¬ 
portional  to  the  square  root  of  the  tension.”  A  thicker  cord  not  so  tightly 
stretched  would  be  the  parallel  to  red  light. 

- 4. - 

SOURCES  OF  LIGHT. 

At  the  various  instrument-makers’  cases  containing  four  or  five  tubes,  filled 
with  white  powders  and  hermetically  sealed,  are  to  be  obtained.  When  the 
tubes  are  observed  in  a  dark  room  (and,  of  course,  before  exposure  to  light), 
they  are  invisible  ;  if.  however,  a  piece  of  magnesium  wire  is  now  burnt  close 
to  the  tubes,  they  will  be  found  to  shine  in  the  dark  and  to  emit  various 
coloured  rays  of  faint  light.  To  this  curious  effect  is  given  the  name  of  phos¬ 
phorescence  ;  and  when  the  same  result  is  obtained  by  exposing  the  tubes  to 
the  lijiht  of  the  sun,  the  resulting  phenomenon  is  denominated  phosphorescence 
after  insolation,  /.<?.,  after  exposure  to  the  sun.  The  chemical  substances 
which  possess  the  property  of  developing  light  after  exposure  to  light  are 

2 — 2 


20 


ON  LIGHT. 


called  phosphori,  and  the  best  are  the  diamond,  Bolognian  phosphorus,  or 
Bologna  stone,  made  from  sulphate  of  baryta,  which  occurs  in  nature  as  a 
mineral,  and  is  called  heavy  spar  or  barytine.  It  is  prepared  by  heating  this 
mineral  with  charcoal  to  a  dull  red  heat,  or  by  the  process  of  Margraf,  ii 
which  the  mineral  is  powdered,  mixed  with  flour,  and  made  red  hot ;  or  more 
amusingly  by  the  process  of  Daguerre,  who  uses  a  marrow-bone  for  his 
crucible,  and,  after  it  is  freed  from  fat  and  thoroughly  dried,  tills  it  with  heavy 
spar,  powdered  in  any  #<?«-metallic  mortar.  The  bone  is  now  closed  with  a 
clay  lute,  and  inclosed  in  an  iron  tube,  which  is  surrounded  with  fine  clay, 
and  the  whole  exposed  for  three  hours  to  a  red  heat  in  a  furnace.  The  sub¬ 
stance  which  produces  the  effect 
is  a  sulphuret  of  barium.  In  the 
same  manner  strontian  phos¬ 
phorus  is  obtained  from  coelestin. 

Canton’s  phosphorus  is  pre¬ 
pared  bv  exposing  a  mixture  of 
three  parts  of  sifted  and  calci  ed 
oyster-shells  and  one  part  of 
flowers  of  sulphur  to  a  strong  fire 
for  one  hour.  There  are  also 
many  other  phosphori  ;  amongst 
these  may  be  enumerated  Os- 
ann’s  phosphori,  Wach’s  phos¬ 
phori,  Homberg's  phosphorus, 

Baldwin’s  phosphorus,  and  many 
kinds  of  fluor  spar. 

The  phosphorescence  of  these 
various  bodies,  unlike  that  of  the 
curious  element  phosphorus,  is 
produced  independently  of  any 
chemical  change  ;  and  if  en¬ 
closed  in  sealed  glass  tubes, 
and  excluded  from  light,  they 
may  retain  the  property  of  show¬ 
ing  phosphorescence  for  manv 
years,  whilst  the  light  emitted 
from  phosphorus  is  due  to  the  slow  oxidation  of  this  element ;  and  if  this  is 
arrested,  by  placing  it  in  water,  or  in  any  gas,  like  nitrogen,  the  light  is  no 
longer  produced.  Upon  what  principle,  then,  is  it  possible  to  explain  the  cause 
of  the  emission  of  light  after  exposing  phosphori  to  the  sun  or  any  brilliant 
artificial  light? 

The  most  rational  theory  which  can  be  suggested  is,  that  the  undulations 
of  light  convey  their  own  vibratory  motions  to  the  phosphori,  just  as  one 
musical  instrument  may  cause  another  to  vibrate  sympathetically  with  it,  and 
phosphorescence  is  observed  so  long  ag  the  substance  continues  to  vibrate. 
In  a  dark  100m,  and  without  a  constant  accession  or  supply  of  vibratory  power, 
the  light  becomes  fainter  and  fainter,  until  it  is  no  longer  capable  of  affecting 
the  eye  ;  the  vibratory  power,  like  any  other  mechanical  motion,  must  come 
to  an  end  when  cut  off  from  its  source  of  power,  when,  as  in  this  case,  it  is 
removed  from  the  greater  vibratory  power,  the  sun  or  the  burning  magnesium, 
which  originally  set  it  in  motion.  This  opinion  is  further  confirmed  when  we 


SOURCES  OF  LIGHT. 


21 


take  into  account  the  large  number  of  substances  which  may  become  phos¬ 
phorescent  in  a  tolerably  high  degree.  If  this  property  was  confined  to  a  few 
bodies,  the  theory  might  not  be  so  applicable  ;  but  if  it  is  agreed  beforehand 
that  any  particles  may  become  luminous  if  they  are  capable  of  entering  into 
that  state  of  vibration  which  we  suppose  belongs  to  the  sun  and  artificial 
sources  of  light,  then  it  can  be  understood  why  the  following  organic  or 
inorganic  substances  are  all  considered  to  enjoy  in  a  limited  degree  the  pro¬ 
perty  of  phosphorescence  after  exposure  to  the  sun : — crystallized  boracic  acid, 
sal  ammoniac,  sulphate  of  potash,  nitre,  crystallized  carbonate,  borate,  or 
sulphate  of  soda,  rock  salt,  witherite,  radiating  heavy  spar  from  Bologna, 
manenglas,  fibrous  gypsum,  alabaster,  artificial  sulphate  of  lime,  common 
fluor  spar,  crystallized  sulphate  of  magnesia,  crystallized  alum,  arsenious 
acid,  pharmacolite.  freshly  prepared  flowers  of  zinc,  sulphate  of  mercury, 
tartar,  benzoic  acid,  loaf  sugar,  sugar  of  milk,  bleached  wax,  white  paper 
(especially  when  it  has  been  heated  almost  to  burning),  yellow  and  red  paper, 
which  are  nearly  as  phosphorescent  as  white  paper,  egg-shells,  corals,  snails, 
pearls,  bones,  teeth,  ivory,  leather,  and  skins  of  men  and  animals,  tartaiic 
acid,  also  seeds,  grain,  flour,  starch,  crumbs  of  bread,  gum  arabic,  feathers, 
cheese,  yolk  of  egg,  muscular  flesh,  tendons,  isinglass,  glue,  horn,— all  well 
dried  ;  moreover,  the  albumen  of  trees,  bleached  linen,  bleached  cotton  yarn, 
and  other  bleached  vegetable  fibres.  The  above  is  only  a  small  instalment  of 
the  different  chemical  bodies  and  common  substances  which  Gmelin  enume¬ 
rates  when  he  speaks  of  those  things  which  become  phosphorescent  by  irradia¬ 
tion.  Phosphorescence  may  also  be  further  developed  by  heat,  mechanical 
force,  and  crystallization,  all  of  which  are  modes  of  motion,  and  suggest  the 
setting  up  of  a  vibratory  effect,  resulting  in  the  production  of  light.  Chemical 
action,  another  mode  of  motion,  is  concerned  in  the  phosphorescence  ot  live 
animals  and  putrefying  animal  matter,  and  also  in  the  production  of  the  same 
effect  in  living  and  decaying  plants. 

Heat  a  Source  of  Light. 

When  iron  is  heated  to  a  temperature  of  635°  Fahrenheit,  it  emits  a  dull  red 
light,  visible  only  in  a  darkened  room.  If  the  heat  is  further  increased  to  903 
Fahrenheit,  a  bright  red  light  is  apparent,  visible  in  a  chamber  tairly  illumi¬ 
nated.  The  light  attains  a  greater  intensity  at  the  moment  the  iron  is  heated 
to  iooo°  Fahrenheit.  1'hus,  by  the  progressive  increase  of  the  heat  ot  the 
iron,  what  is  called  a  dull  red,  a  pale  red,  and  a  white  heat  is  obtained.  By 
increasing  the  heat  of  a  solid  body  a  development  ot  light  or  incandescence 
is  obtainable.  It  is  contended  that  heat  and  light  are  only  differences  ot  wave¬ 
lengths. 

Light  the  frequent  attendant  of  Electrical  Phenomena. 

The  intense  and  dazzling  brightness  of  lightning  has  been  known  to  cause 
temporary  and  permanent  blindness.  The  immense  electric  spark,  the  result 
of  the  discharge  of  thousands  of  acres  of  charged  clouds,  is  more  closely  imi¬ 
tated  than  ever  by  large  induction  coils,  constructed  by  Mr.  Apps  for  the 
Royal  Polytechnic  and  also  for  Mr.  Spottiswoode.  At  the  moment  ot  dis¬ 
charge  the  electricity  may  develop  light,  heat,  ntagnetical,  mechanical,  and 
chemical  effects.  Here  is  a  correlation  of  forces  that  might  well  excuse 
Oersted  in  proposing  a  theory  of  light  in  which  he  regards  light  as  the  result 
of  electric  sparks. 


22 


ON  LIGHT. 


[ From  the  “  Proceedings  of  the  Royal  Society ,”  No.  1 15,  1869.] 

Author’s  Experiments  with  the  Great  Induction  Coil  at  the 

Royal  Polytechnic. 

The  length  of  the  coil  from  end  to  end  is  9  ft.  10  in.,  and  the  diameter  2  ft. ; 
the  whole  is  cased  in  ebonite  ;  it  stands  on  two  strong  pillars  covered  with 
ebonite,  the  feet  of  the  pillars  being  22  in.  in  diameter.  The  ebonite  tubes, 
&c..  are  the  largest  ever  constructed  at  Silvertown  Works. 

The  total  weight  of  the  great  coil  is  15  cwt.,  that  of  the  ebonite  alone  being 
477  lbs. 

I  am  indebted  to  Mr.  Apps  for  the  following  details.  The  primary  wire  is 
made  of  copper  of  the  highest  conductivity,  and  weighs  145  lbs  ;  the  diameter 
of  this  wire  is  '0925  of  an  inch  and  the  length  3,770  yards.  The  number  of 
revolutions  of  the  primary  wire  round  the  core  of  soft  iron  is  6,000,  its 
arrangement  being  3,  6,  and  12  strands. 

The  total  resistance  of  the  primary  is  2*201400  British  Association  units  ; 
and  the  resistances  of  the  primary  conductors  are,  respectively,  for  three 
strands,  733800  B.A.U.,  six  *366945  B.A.U.,  twelve  *1834725  B.A  U. 

The  primary  core  consists  of  extremely  soft  straight  iron  wires  5  ft.  in  length, 
and  each  wire  is  *0625  of  an  inch  in  diameter.  The  diameter  of  the  combined 
wires  is  4  in.,  and  their  weight  is  123  lbs. 

The  secondary  wire  is  150  miles  in  length  ;  it  is  covered  with  silk  through¬ 
out  ,  and  the  average  diameter  is  *oi  5  of  an  inch. 

The  total  weight  of  this  wire  is  606  lbs.,  and  the  resistance  33  560  B.  A.  units. 
The  insulation  throughout  is  greater  by  95  per  cent,  than  the  strain  upon  the 
coil  during  its  action.  The  secondary  wire  is  insulated  from  the  primary  by 
means  of  an  ebonite  tube  half  an  inch  in  thickness  and  8  ft.  in  length. 

The  le  ngth  of  the  secondary  coil  is  54  in.,  the  diameter  is  19  in.,  and,  with¬ 
out  the  internal  ebonite  tube  containing  the  primary  wire  and  iron  core,  it  is 
a  hollow  cylinder  19  in.  in  diameter  and  6  in.  thick. 

The  condenser,  made  in  the  usual  manner  with  sheets  of  varnished  paper 
and  tinfoil,  is  arranged  in  six  parts,  each  containing  125  superficial  feet,  or 
750  square  feet  of  tinfoil  in  the  whole. 

A  large  and  substantially  made  contact-breaker,  detached  from  the  great 
coil  and  worked  by  an  independent  electro-magnet,  was  constructed  and 
worked  very  well  with  a  comparatively  moderate  power  of  10  or  20  large 
Bunsen’s  cells  ;  when,  however,  the  battery  was  increased  to  30  or  40  cells,  it 
became  unmanageable. 

A  Foucault  break,  with  the  platinum  amalgam  and  alcohol  above  it,  was 
now  tried,  and  answered  very  much  better  than  the  ordinary  contact-breaker  : 
there  was  no  longer  any  burning  or  destruction  of  the  contact  points,  although 
the  great  power  of  the  instrument  appeared  to  cause  continued  decomposition 
in  the  water  of  the  alcohol  placed  above  the  platinum  amalgam,  and  the  spirit 
was  frequently  ejected,  probably  by  explosion  of  the  mixed  gases  taking  place 
in  the  amalgam,  in  which  they  collected  in  bubbles  ;  the  alcohol  took  fire  con¬ 
stantly,  and  had  to  be  extinguished.  A  large  and  very  strong  glass  vessel- 
in  fact,  the  inverted  glass  cell  of  a  bichromate  battery — was  bored  through, 
and  the  neck  fitted  into  a  cap  with  cement,  a  thick  wire  covered  with  platinum 
being  inserted  in  the  cap  ;  the  platinum  amalgam  was  poured  on  this,  and  over 
it  a  pint  of  alcohol  ;  the  contact  wire  was  also  very  large,  and  pointed  with  a 
thick  stud  of  platinum,  and,  being  attached  to  a  spring,  contact  was  easily 


SOURCES  OF  LIGHT. 


23 


made  and  broken.  Flashes  of  light  could  be  seen  between  the  amalgam  and 
the  alcohol  ;  but  explosions  did  not  occur,  and  the  height  of  the  column  ot 
the  latter  prevented  the  forcible  ejection  of  the  spirit,  which  no  longer  took 
fire.  This  break  was  used  for  eight  hours  in  a  continuous  series  of  experi¬ 
ments. 

The  Bunsen’s  battery  used  in  the  experiments  was  made  with  the  largest 
porous  cells  that  could  be  obtained,  and  each  cell  contained  about  one  pint 
of  nitric  acid,  the  immersed  carbon  being  50  superficial  inches  in  each  cell. 

The  resistance  of  a  single  cell  of  this  large  Bunsen  battery  was  found  t»  be 
•2585  B.A.U. 

In  the  following  experiments  the  battery  was  arranged  for  intensity,  and 
used  with  the  complete  condenser  of  750  square  feet  of  tinfoil  and  2,000  square 
feet  of  paper  in  1,500  sheets. 


Number  of  cells 
of  battery. 

5  .  .  complete  condenser 


10 

yy 

yy 

15 

yy 

yy 

20 

yy 

yy 

25 

yy 

yy 

30 

yy 

yy 

35 

V 

yy 

40 

yy 

50 

yy 

yy 

Length  of  spark. 

inches. 

.  I2"0 

.  i4-o 

•  17-5 

,  21-25 

.  2  VO 

■  23-5 
.  260 

•  27-5 

.  28-0  to  29-0 


The  longest  spark  yet  obtained  is  therefore  29  in.  in  length. 

In  order  to  ascertain  whether  any  variation  in  the  size  of  the  condenser  (of 
which,  as  already  stated,  1,  2,  3,  4,  5,  or  6  parts  could  be  used)  would  affect 
the  length  of  the  spark,  a  number  of  experiments  were  tried  ;  and  it  will  be 
noticed  in  the  tabulated  results  that  when  half  the  condenser  was  used  the 
spark  increased  in  length  up  to  20  cells,  but  not  after.  The  experiment  of 
dividing  the  condenser  and  using  one-half  led  to  a  very  serious  accident,  and 
the  coil  was  rendered  useless  for  a  time  by  the  destruction  of  the  insulating 
material  of  a  part  of  the  primary  coil  ;  the  particular  strands  affected  threw 
out  minute  spicula  of  metal,  which  communicated  with  each  other,  and  the 
battery-current,  instead  of  passing  through  1,257  yards,  now  only  traversed  a 
very  short  length.  The  accident,  however,  proved  to  be  useful,  inasmuch  as 
it  showed  that  the  coil  could  be  easily  taken  to  pieces  and  repaired  in  a  com¬ 
paratively  short  space  of  time.  In  the  annexed  table  the  experiments  with 
the  half  of  the  condenser  are  marked  with  a  cross. 


Length  of 

Number  of 

spark. 

cells. 

inches. 

5  • 

full  condenser 

• 

I  2  "OO 

yy 

reduced  } 

• 

IO75 

yy 

0 

yy 

. 

13’°° 

yy 

one- half  or  £ 

+  . 

J3‘50 

yy 

reduced  £ 

. 

1300 

yy 

A 

»  6 

• 

1175 

IO  . 

full  condenser 

, 

14-00 

yy 

reduced  J 

0 

yy  ft 

. 

15-00 

yy 

• 

1575 

IO  . 

one- half  % 

+  • 

1800 

Length  of 

Number  of  spark, 

cells.  inches. 

10  .  reduced  .  .  17-25 

f>  I  7 

51  o  *  *  •  1  / 

20  .  full  condenser.  .  21*25 

„  .  reduced  one-half  +  22 

30  .  full  condenser.  .  23-5 

„  .  reduced  one-half  -f-  23-5 

40  .  full  condenser .  .  25  0 

„  .  one-half  .  .  +250 

50  .  full  condenser .  .  28 

„  .  one-half  .  .  -j-  28 


24 


ON  LIGHT. 


Experiments  were  now  tried  to  ascertain  whether  any  increase  in  the  length 
of  the  spark  could  be  obtained  by  arranging  the  battery  and  the  primary  coil 
for  quantity. 


inches. 

5+  5  cells,  length  of  spark  .  .  .  1 4'5 

io+io  cells,  „  . i8'o 

20  +  20  cells,  „  2175 

25+25  cells,  „  2375 

I5  +  J5  +  I5  cells,  „  . 20 '00 


It  is  evident  that  no  material  advantange  was  obtained  by  the  above 
arrangement  except  in  the  first  experiment ;  and  even  where  three  groups 
were  connected,  as  in  the  last  experiment,  a  decrease  in  the  length  of  the 
spark  is  observed  when  compared  with  the  45  or  50  cells  arranged  for 
intensity,  the  difference  being  as  20  to  28. 

The  spark  obtained  from  the  large  coil  presents  some  novel  and  curious 
features.  It  is  thick  and  flame-like  in  its  appearance,  and  therefore  it  will  be 
alluded  to  as  the  “  flaming  spark.” 

When  the  discharging-point  and  circular  plate  are  brought  within  6  or  7 
inches  of  each  other,  the  flaming  nature  of  the  spark  becomes  still  more 
apparent. 

Two  light  yellow  flames  curving  upwards  appear  to  connect  the  opposite 
poles.  If  a  blast  of  air  from  powerful  bellows  is  directed  against  the  flaming 
spark,  the  flaming  portion  can  be  blown  away  and  increased  in  area  ;  and 
thin  wiry  sparks  are  now  seen  darting  through  it,  sometimes  in  one  continuous 
stream,  at  another  time  divided  into  three  or  more  sparks,  all  following  the 
direction  in  which  the  flame  is  blown. 

The  heat  of  this  is  very  great,  and,  if  passed  through  asbestos  (supported 
on  an  insulating  pillar),  quickly  causes  the  latter  to  become  red  hot. 

When  powdered  charcoal  is  shaken  from  a  pepper-box  into  the  flaming 
spark  in  a  vertical  line  and  in  considerable  quantities,  the  greater  part  of  the 
light  is  obscured,  and  the  whole  form  of  the  flaming  spark  presents  the 
appearance  of  a  black  cloud,  with  a  line  of  brightly  ignited  particles  fringing 
the  lower  parts.  If  the  charcoal  is  dusted  through  in  small  quantities,  each 
particle  becomes  ignited,  like  charcoal  blown  into  a  hydrogen  flame. 

When  the  flaming  spark  is  directed  on  to  a  glass  plate  upon  which  a  little 
solution  of  lithium  chloride  is  placed,  the  latter  colours  the  flame  upwards  to 
the  height  of  3  or  4  inches  in  the  most  beautiful  manner  ;  and  if  the  point  of 
the  discharge  is  tipped  with  paper  or  sponge  moistened  with  a  little  solution 
of  sodium  chloride,  the  two  colours  (the  yellow  from  the  salt  and  the  crimson 
from  the  lithium)  meet  each  other,  a  neutral  point  being  found  about  half-way, 
thus  illustrating  apparently  the  dual  character  of  electricity,  and  that  +  passed 
to  —  electricity,  and  vice  versa. 

The  flaming  spark  can  be  obtained  in  perfectly  dry  air. 

Whilst  passing  through  common  air,  if  blown  against  a  sheet  of  damp 
litmus-paper,  the  latter  is  rapidly  changed  red.  In  order  to  ascertain  whether 
the  acid  product  was  nitric  acid,  the  flaming  spark  (9  or  10  inches  in  length) 
was  passed  through  a  tube  connected  by  a  cork  and  bent  tube  with  a  bottle 
containing  distilled  water,  from  which  another  tube  passed  to  the  air-pump  ; 
on  drawing  the  air  slowly  over  the  spark,  and  passing  the  former  into  the 
bottle,  nitric  acid  was  obtained  in  large  quantities—so  much  so  that  it  could 


SOURCES  OF  LIGHT. 


25 


be  detected  by  the  smell  and  taste  as  well  as  by  the  ordinary  tests.  The 
popular  notion  that  nitric  acid  is  always  produced  during  a  thunder-storm 
would  therefore  appear  to  be  correct.  To  determine  the  effect  of  a  cooling 
surface  on  the  flaming  spark,  a  hole  in.  in  diameter  was  bored  through 
a  thick  block  of  Wenham  Lake  ice,  and  the  spark  passed  through  the  air  in 
the  tube  of  ice  ;  no  change  took  place,  and  the  spark  was  still  a  flaming 
one. 

When  the  spark  was  received  on  the  ice,  it  lost  its  flaming  character,  and 
became  thin  and  wiry,  spreading  out  in  all  directions. 

If  the  discharging-wires  were  tipped  with  ice,  the  spark  was  always  flaming 
when  any  thickness  of  air  intervened  between  them.  Even  over  the  ice,  if  the 
spark  passed  a  fraction  of 
an  inch  above  the  surface, 
it  was  always  a  flaming 
one,  but  changed  to  the 
thin  spark  when  the  point 
of  the  discharging  -  wire 
was  thrust  into  the  ice.  If 
one  of  the  discharging- 
wires  of  the  great  coil  is 
brought  to  the  centre  of  a 
large  swing  looking-glass, 
and  the  other  wire  con¬ 
nected  with  the  amalgam 
at  the  back,  the  sparks 
are  thin  and  wiry, arbores¬ 
cent,  and  very  bright  (see 
Fig.  k),  the  crackling  noise 
of  these  discharges  being 
quite  different  from  that 
of  the  heavy  thud  or  blow 
delivered  by  the  flaming 
spark. 

When  the  discharging- 
wire  is  brought  close  to  the 
frame  of  the  looking-glass, 
or  if  a  sufficient  thickness 

of  air  intervenes,  the  spark  F IG.  E. 

again  becomes  flaming ; 
or,  as  sometimes  occurs,  if  the  discharging-wire  is  placed  about  5  in.  from  the 
frame,  the  spark  is  partly  flaming  and  partly  wiry,  i.e.,  when  it  impinges  on 
the  glass. 

The  examination  of  the  flaming  spark  with  the  spectroscope  has  not  as  yet 
settled  anything  definitely.  The  spectrum  is  a  continuous  one  with  the  sodium 
line.  When  the  blast  of  air  is  used,  and  the  wiry  sparks  made  apparent,  then 
the  nitrogen  line  appears. 

The  flaming  spark  has  been  ascribed  by  some  experienced  observers  to 
the  incandescence  of  the  dust  in  the  air,  and  especially  sodium  chloride. 

If  the  salt,  & c.,  is  thus  made  hot,  can  the  air  in  which  it  is  mechanically 
diffused  remain  cool  ? 

Is  not  the  salt,  &c.,  in  the  same  condition  as  a  platinum  wire  held  in  the 


26 


ON  *. LIGHT 


non-luminous  part  of  the  hot  burnt  gas  escaping  from  the  chimney  of  an 
Argand  burner? 

Will  gaseous  elements  when  combining  (and  in  this  case  the  nitrogen  and 
oxygen  do  unite,  as  proved  by  the  formation  of  nitric  acid)  give  a  continuous 
spectrum  ? 

To  ascertain  whether  the  “flaming  spark”  could  be  obtained  with  a  small 
number  of  cells,  the  large  Bunsen’s  battery  was  reduced  to  3  cells  ;  and  it  was 
found  that  no  appreciable  spark  could  be  produced  when  the  whole  primary 
wire  was  used  with  less  than  5  cells. 

By  reducing  the  length  of  the  primary  wire,  and  using  the  four  divisions 
separately,  the  following  results  were  arrived  at : 


Five  cells. 

inches. 

1st  section,  nearest  core 

... 

wiry 

spark. 

2nd  „ 

— •  •  • 

6|, 

99 

3rd  „ 

•  •  • 

4t, 

99 

4th  „ 

. 

6|, 

99 

Ten  cells. 

inches. 

1st  section,  nearest  core 

•  •  • 

8i  wiry 

spark. 

2nd  „ 

•  •  • 

8f, 

9» 

3rd 

4th 


99 

99 


8,  bright  blue  wiry  spark. 
9f ,  slightly  flaming. 


Fifteen  cells. 


inches. 

1st  section,  nearest  core 

.  . 

10,  slightly  flaming. 

2nd 

99 

•  . 

T  O— 

•  1W8’  99  99 

3rd 

99 

•  . 

•  91  *9 

.  1 1 1,  flaming  spark. 

4th 

99 

• 

Twenty  cells. 

inches. 

1st  section,  nearest  core 

1 1  b,  flaming  spark. 

2nd 

99 

. 

.12, 

3rd 

99 

• 

•  it, 

4th 

99 

• 

•  I2i 

If  the  two  wires  from  the  secondary  coil  are  placed  in  water,  no  spark  is 
perceptible,  even  when  they  are  brought  very  close  together,  until  they  touch. 

If  the  negative  wire  is  passed  through  a  cork,  on  which  a  glass  tube  (a 
lamp-glass)  is  fixed  containing  a  depth  of  5  inches  of  water,  and  the  positive 
wire  is  brought  within  half  an  inch  of  the  surface  of  the  water  in  the  tube,  it 
becomes  red  hot  ;  and  if  drawn  farther  away  from  the  surface,  the  upper  part 
of  the  tube  is  filled  with  a  peculiar  glow  or  light  abounding  in  Stokes’s  rays. 

The  experiments  with  the  vacuum-tubes,  and  especially  Gassiot’s  cascade, 
are,  as  might  be  expected,  very  beautiful.  When  a  coal-gas  vacuum-tube  of 
considerable  diameter,  and  conveying  the  full  discharge  from  the  secondary 
coil,  is  supported  over  a  powerful  electro- magnet  axially,  the  discharge  is  con¬ 
densed  and  heat  is  produced. 

If  placed  equatoriallv,  the  heat  increase  s  greatly  ;  the  discharge  is  condensed 
and  impinges  upon  the  sides  of  the  glass  tube,  which  becomes  too  hot  to 


SOURCES  OF  LIGHT. 


27 


touch  ;  and  if  the  experiment  had  been  continued  too  long,  no  doubt  the  tube 
would  have  cracked. 

The  enormous  quantity  of  electricity  of  high  tension  which  the  coil  evolves 
when  connected  with  a  battery  of  40  cells,  is  shown  by  the  rapidity  with  which 
it  will  charge  a  Leyden  battery. 

Under  favourable  circumstance-,  three  contacts  with  the  mercurial  break 
will  charge  40  square  feet  of  glass. 

Mr.  Gassiot  was  present  on  one  occasion,  and  particularly  observed  with 
myself  the  rapidity  with  which  a  series  of  twelve  large  Leyden  jars  arranged 
in  cascade  were  discharged.  The  noise  was  great,  and  each  time  the  spark 
(which  was  very  condensed  and  brilliant)  struck  the  metallic  disc,  the  latter 
emitted  a  ringing  sound,  as  if  it  had  received  a  sharp  blow  from  a  small 
hammer. 

The  discharges  were  made  from  a  point  to  a  metallic  disc  ;  and  when  the 
former  was  positive,  the  dense  spark  measured  from  18^  to  i8f  in.,  and 
fell  to  8£  in.  when  the  metallic  plate  was  positive  and  the  point  negative. 

A  variation  of  the  Leyden  jar  experiments  was  tried,  by  connecting  the  coil 
worked  by  a  quantity  battery  of  25  +  25  cells  with  six  Leyden  jars  arranged  in 
cascade,  and  the  spark  obtained  measured  8|  in. 

The  same  six  jars  connected  with  the  coil  when  the  50  cells  were  arranged 
continuously  for  intensity  gave  a  spark  of  12  in.  of  very  great  density  and 
brilliancy. 

Other  experiments  are  being  tried  with  the  great  coil,  the  results  of  which 
will  be  duly  brought  before  the  Society  if  thoight  of  sufficient  importance. 

The  experiments  made  with  the  great  Polytechnic  coil  have  nc  doubt  con¬ 
tributed  a  large  amount  of  experience,  and  led  to  the  construction  of  a  still 
more  effective  instrument  for  William  Spottiswoode,  Esq.,  F.R.S.,  which  is 
thus  described  by  that  gentleman  : 

[From  the  “  Philosophical  Magazine”  for  January ,  187 7.] 

Description  of  a  Large  Induction  Coil.  By  William 
Spottiswoode,  F.R.S. 

Although  I  have  not  as  yet  many  experimental  results  sufficiently  complete 
for  communication  to  your  magazine,  I  still  think  that  the  construction  of  an 
induction  coil  capable  of  giving  a  spark  42  in.  in  length  is  an  instrumental 
feat  deserving  of  record  in  the  annals  of  science.  1  therefore  venture  to 
submit  the  particulars  of  this  coil,  recently  completed  for  me  by  Mr.  Apps,  of 
433  Strand,  to  whose  skill  and  perseverance  the  success  of  the  undertaking 
is  due. 

The  general  appearance  of  the  instrument  is  represented  in  the  following 
figure,  by  which  it  is  seen  that  the  coil  is  supported  bv  two  massive  pillars  of 
wood  sheathed  with  gutta-percha,  and  filled  in  towards  their  upper  extremi¬ 
ties  with  paraffin  wax.  Besides  these  two  main  supports,  a  third,  capable  of 
being  raised  or  lowered  b/  means  of  a  screw,  is  placed  in  the  centre,  in  order 
to  prevent  any  bending  of  the  great  superincumbent  mass.  The  whole  stands 
on  a  mahogany  frame  resting  on  castors. 

The  coil  is  furnished  with  two  primaries,  either  of  which  may  be  used  at 
pleasure.  Either  may  be  replaced  by  the  other  by  two  men  in  the  course  of 
a  few  minutes.  The  one  to  be  used  for  long  sparks,  and  indeed  for  most 
experiments,  has  a  core  consisting  of  a  bundle  of  iron  wires  each  *032  in. 
thick,  and  forming  together  a  solid  cylinder  44  in.  in  length  and  3  5625  in.  in 


28 


ON  LIGHT. 


diameter.  Its  weight  is  67  lbs.  The  copper  wire  used  in  this  primary  is  66d 
jards  in  length,  o. 6  in.  in  diameter,  has  a  conductivity  of  93  per  cent.,  and 
offers  a  total  resistance  of  2'3  ohms.  It  contains  1,344  turns  wound  singly  in 
six  layers,  has  a  total  length  of  42  in  ,  with  an  internal  diameter  of  3  75  in.  and 
an  external  of  475  in.  The  total  weight  of  this  wire  is  55  lbs. 

The  other  primary,  which  is  intended  to  be  used  with  batteries  of  greater 
surface,  e.g.,  for  the  production  of  short  thick  sparks,  or  for  spectroscopic 
purposes,  has  a  core  of  iron  wires  ‘032  in.  thick,  forming  a  solid  cylinder  44 
in.  long  and  3  8125  in  diameter.  The  weight  of  this  core  is  92  lbs.  The 
copper  wire  is  similar  to  that  in  the  primary  first  described  ;  but  it  consists 
of  504  yards  wound  in  double  strand,  forming  three  pairs  of  layers  whose 
resistances  are  ‘  1 8 1 ,  ’2ii,  '231  ohms  respectively.  Its  length  is  42  in.,  its 
external  diameter  5 '5,  and  its  internal  4  in.  Its  weight  is  84  lbs.  By  a  some¬ 
what  novel  arrangement,  these  three  layers  may  be  used  either  in  series  as  a 
wire  of  ‘192  in.  thickness,  or  coupled  together  in  threes  as  one  of  576  in. 
thickness.  It  should,  however,  be  added  that,  owing  to  the  enormous  strength 
of  current  which  this  is  capable  of  carrying,  and  to  the  highly  insulated 
secondary  coil  being  possibly  overcharged  so  as  to  fuse  the  wire,  this  larger 
primary  is  best  adapted  for  use  with  secondary  condensers  of  large  surface, 
for  spectrum  analysis,  and  for  experiments  with  vacuum-tubes  in  which  it  is 
desirable  to  produce  a  great  volume  of  light  of  high  intensity  as  well  as  of 
long  duration  at  a  single  discharge.  The  a  ternate  discharges  and  flaming 
sparks  can  also  be  best  produced  by  this  primary.  It  has  been  used  for 
high-tension  sparks  to  34  in.  in  air,  the  battery  being  10  cells  of  Grove’s  with 
platinum  plates  6^X3  in.  Great  facilities  for  the  use  of  different  sets  of 
batteries  are  afforded  by  the  division  of  this  primary  into  three  separate 
circuits,  to  be  used  together  or  separately  ;  and  by  a  suitable  arrangement  of 
automatic  contact-breakers,  the  primary  currents  may  be  made  to  follow  in 
a  certain  order  as  to  time,  duration,  and  strength,  with  effects  which,  when 
observed  in  the  revolving  mirror,  will  doubtless  lead  to  important  results  in 
the  study  of  striae  in  vacuum-tubes. 

We  now  come  to  the  secondary,  which  consists  of  no  less  than  280  miles  of 
wire,  forming  a  cylinder  37 *5  in.  in  length,  20  in.  in  external,  and  9^5  in.  in 
internal  diameter.  Its  conductivity  is  94  per  cent.,  and  its  total  resistance  is 
equal  to  110,200  ohms.  The  whole  is  wound  in  four  sections,  the  diameter  of 
the  wire  used  for  the  two  central  sections  being  "0095  in.,  and  those  of  the  two 
external  being  01  1 5  in.  and  '01 10  in.  respectively.  The  object  of  the  increased 
thickness  towards  the  extremities  of  the  coil  was  to  provide  for  the  accumulated 
charge  which  that  portion  of  the  wire  has  to  carry. 

Each  of  these  sections  was  wound  in  flat  discs  ;  and  the  average  number  of 
layers  in  each  disc  is  about  200,  varying,  however,  with  the  different  sizes  of 
wire,  &c.  The  total  number  of  turns  in  the  secondary  is  341,850. 

The  great  length  of  the  wire  necessary  can  be  easily  understood  from  the 
fact  that  near  the  exterior  diameter  of  the  coil  a  single  turn  exceeds  5  ft.  in 
length.  The  spark,  it  is  believed,  is  due  to  the  number  of  turns  of  wire,  rather 
than  to  its  length,  suitable  insulation  being  preserved  throughout  the  entire 
length.  In  order  to  insure  success,  the  layers  were  carefully  tested  separately 
and  then  in  sets,  and  the  results  noted  for  comparison.  In  this  way  it  was 
hoped  that  step  by  step  safe  progress  would  be  made.  As  an  extreme  test,  as 
many  as  70  cells  of  Grove’s  have  been  used,  with  no  damage  whatever  to  the 
insulation. 

The  condenser  required  for  this  coil  proves  to  be  much  smaller  than  might 


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30 


ON  LIGHT. 


at  first  have  been  expected.  After  a  variety  of  experiments,  it  appeared  that 
the  most  suitable  size  is  that  usually  employed,  by  the  same  maker,  with  a 
io  in.  spark  coil,  viz.,  126  sheets  of  tinfoil  18  X  8‘25  in.  in  surface,  separated  by 
two  thicknesses  of  varnished  paper,  the  two  thicknesses  measuring ‘oi  1  in. 
The  whole  contains  252  sheets  of  paper  19x9  in.  in  surface.  I  hope,  at  some 
future  opportunity,  to  make  further  experiments  with  other  condensers. 

Using  the  smaller  primary,  this  coil  gave,  with  5  quart  cells  of  Grove,  a 
spark  of  28  in.,  with  10  similar  cells  one  of  35  in.,  and  with  30  such  cells  one 
of  37'5  in.,  and  subsequently  one  of  42  in.  As  these  sparks  were  obtained 
without  difficulty,  it  appears  not  improbable  that,  if  the  insulation  of  the  ends 
of  the  secondary  were  carried  further  than  at  present,  a  still  longer  spark 
might  be  obtained.  But  special  adaptations  would  be  required  for  such  an 
experiment,  the  spark  of  42  in.  already  so  much  exceeding  the  length  of  the 
secondary  coil. 

When  the  discharging  points  are  placed  about  an  inch  apart,  a  flowing  dis¬ 
charge  is  obtained  both  at  making  and  at  breaking  the  primary  circuit.  The 
CAund  which  accompanies  this  discharge  implies  that  it  is  intermittent,  the 
time  and  current-spaces  of  which  have  not  as  yet  been  determined. 

With  a  28  in.  spark,  produced  by  5  quart  cells,  a  block  of  flint  glass  3  in. 
in  thickness  was  in  some  instances  pierced,  in  others  both  pierced  and 
fractured,  the  fractured  pieces  being  invariably  flint  glass.  If  we  may 
estimate  from  this  result,  the  42  in.  spark  would  be  capab  e  of  piercing  a 
block  6  in.  in  thickness. 

When  used  for  vacuum-tubes,  this  coil  gives  illumination  of  extreme  bril¬ 
liancy  and  very  long  duration:  with  20  to  30  cells  and  a  slow-working  mercury 
break,  giving,  say,  80  sparks  per  minute,  the  striae  last  long  enough  for  their 
forward  and  backward  motion  to  be  perceived  directly  by  the  unassisted  eye. 
The  appearance  of  the  striae  when  observed  in  a  revolving  mirror  (as  described 
in  the  “  Proceedings  of  the  Royal  Society,”  vol.  xxv.  p.  73)  was  unprecedentedly 
vivid,  and  this  even  when  only  two  or  three  cells  were  employed. 

Chemical  Combination  a  Source  of  Light. 

Finely  divided  lead  or  iron  shaken  from  a  tube  into  the  air  or  oxygen 
oxidizes  rapidly,  burns,  and  emits  light.  Finely  powdered  antimony  unites 
rapidly  with  chlorine  gas,  and  glows  with  the  intensity  of  light  whilst  the 


Fig.  9. — Blotting-papt  r  upon  which  the  Solution  of  Phosphorus  in  Sulphide  . 
of  Carbon  has  been  poured ,  and  then  supported  on  an  iron  wire. 

combination  is  taking  place.  A  solution  of  phosphorus  in  sulphide  of  carbon, 
poured  upon  blotting-paper,  soon  begins  to  evolve  smoke,  produced  during  the 
formation  of  phosphoric  acid,  and  then  rapidly  and  spontaneously  catches  fire 


SOURCES  OF  LIGHT. 


31 


by  the  union  of  the  finely  divided  phosphorus  with  the  oxygen  of  the  air. 
The  name  of  Greek — modernized  into  Fenian— fire  is  given  to  this  solution, 
which  should  only  be  made  and  used  in  small  quantities. 

Is  Mechanical  Force  to  be  regarded  as  a  True  Source  of  Light? 

Since  the  numerous  experiments  made  at  Shoeburyness  with  iron  plates  and 
heavy  guns,  it  has  been  ascertained  over  and  over  again  that  heat  and  fre¬ 
quently  light  are  produced  at  the  moment  the  impact  or  blow  is  given  by  the 
s  iot.  The  mechanical  force,  in  the  abstract,  may  be  regarded  as  the  source 
of  light ;  but  not  perhaps  directly,  as  the  blow  develops  heat,  and  the  latter, 


Arrangement  of  Mechanism  and  Oxy-Hydrogen  Light  required  to  produce  the  effect  of  the  Shadow 
Bloiuiin.  a,  the  mechanical  figure ;  b,  the  lime-tight,  c,  the  handles  used  to  produce  the  movements 
(.1  the  figure. 


probably,  the  light.  It  is  found  that  almost  all  bodies  which  acquire  phos¬ 
phorescence  by  exposure  to  the  sun,  or  insolation,  or  by  heat,  also  become 
luminous  by  friction  or  percussion.  Sometimes  the  light  obtained  by  friction 
is  simply  electrical.  The  sparks  from  a  flint  and  steel  are  due  to  the  com¬ 
bustion  of  minute  particles  of  metal  accelerated  by  the  heat  eliminated  at  the 


32 


ON  LIGHT. 


Fig.  12.  —Effect  in  front  of  the  Curtain. 

moment  the  particle  is  struck  off.  Mechanical  force  can  only  be  regarded 
as  an  indirect  mode  of  producing  light,  because  heat  is  first  developed ;  heat 
is  a  source  of  light,  and  vice  versa. 

From  what  has  been  previously  stated,  it  will  be  understood  that  all  matter 
may  be  divided  in  relation  to  light  into  luminous  and  non-luminous  bodies. 
The  sun  or  a  lighted  lamp  would  represent  the  former,  and  the  moon  with  the 
other  planets,  or  a  piece  of  whitened  board,  the  latter,  because  our  satellite 
shines  by  borrowed  light  from  the  sun,  and  not  by  any  inherent  self-luminosity; 
the  piece  of  board  will  reflect  and  scatter  the  rays  of  light  from  the  lamp, 
and  whilst  doing  this  appears  very  bright.  At  the  same  time  the  board 
obstructs  the  light  and  casts  a  shadow  behind  it,  and  thus  indicates  another 
relation  of  light  to  solid  matter,  called  opacity;  the  opposite  to  this  property 
being  transparency,  whilst  the  intermediate  links  between  opacity  and  trans¬ 
parency  are  termed  semi-transparency,  or  opalescence.  There  are  m&ny  very 
amusing  effects  produced  by  casting  shadows  of  living  or  inanimate  objects 
on  a  transparent  disc  by  the  oxy-hydrogen  light.  (Figs,  io,  11,  12.) 


THE  DIFFUSION  OF  LIGHT. 


OJ 


The  shadow  pantomimic  action  of  living  figures  visible  on  a  transparent 
disc  with  this  strong  light,  and  first  introduced  by  the  author  at  the  Poly¬ 
technic,  has  gone  the  round  of  nearly  all  the  exhibitions  and  theatres  in 
London  and  New  York. 

There  still  remains,  however,  something  new  and  amusing  even  in  this 
hackneyed  branch  of  light.  Mr.  Walker,  jun.,  constructed  a  very  simple 
and  ingenious  piece  of  mechanism,  and  giving  it  the  outline  of  a  human  figure, 
produced  a  good  imitation  of  the  bold  feats  performed  by  Monsieur  Blondin 
on  the  high  rope.  The  shadow  of  the  figure  only  was  projected  on  to  the  disc 
by  the  lime-light,  and  it  simulated  all  the  usual  movements,  such  as  standing, 
walking,  dancing,  and  sitting  astride  the  rope.  Indeed  it  did  rather  more 
than  the  living  prototype,  for  the  figure  stood  on  its  head,  and  threw  the  most 
unnatural  but  highly-amusing  sommersaults.  (Figs  io,  11,  12,  pp.  12,  13.) 


THE  DIFFUSION  OF  LIGHT. 

A  luminous  object  evolves  light  from  every  visible  point  of  its  surface,  and 
if  a  single  point  of  light  were  placed  in  the  centre  of  a  hollow  globe,  every 
portion  of  the  internal  area  would  be  equally  illuminated. 


Fig.  13. — A  Flame  iti  the  centre  of  a  circle ,  throwing  out  rays  in 
every  direction ,  like  the  spokes  of  a  wheel. 

Owing  to  the  manner  in  which  light  is  distributed  and  transmitted  in 
straight  lines  diverging  from  each  other,  its  intensity  diminishes  as  the  square 
of  its  distance  from  the  luminous  source  increases,  and  it  is  on  this  principle 
that  the  instruments  called  photometers,  or  light-measurers,  are  constructed. 

A  scale  of  20  ft.  in  length,  divided  into  feet  and  inches,  may  be  used  in  con¬ 
junction  with  a  box  somewhat  like  a  stereoscope,  containing  two  mirrors 
placed  at  an  angle  of  450,  and  reflecting  the  rays  from  the  two  sources  of 
light  which  are  to  be  confronted  with  each  other.  A  candle,  one  of  six  to  the 

3 


34 


ON  LIGHT. 


pound,  and  burning  so  many  grains  per  minute,  is  fixed  in  a  nozzle,  which 
slides  on  the  scale.  The  box,  which  may  also  slide  or  be  fixed  in  the  centre 
of  the  scale,  reflects  on  one  side  the  light  from  the  lamp  or  gas-burner  which 
is  being  tested,  on  the  other  it  reflects  the  light  of  the  candle.  The  experi¬ 
ment  may  be  conducted  either  by  placing  the  lamp  and  the  candle  at  opposite 
ends  of  the  scale,  and  moving  the  box  with  the  reflectors  until  the  two  spots 
of  light  are  equal  ;  or,  the  box  being  fixed  in  the  centre,  and  the  lamp  under 
examination  placed  at  one  end  of  the  scale,  the  candle  may  be  moved  towards 
the  box  till  the  lights  are  equal,  the  respective  distances  from  the  box  being 
then  squared,  and  the  greater  number  divided  by  the  less,  will  give  the  quo¬ 
tient  which  represents  the  illuminating  power  of  the  lamp  as  compared  with 
the  candle. 


Figs.  14  and  1 5.—  Ritchie's  Photometer. 

Section  of  the  box  containing  the  mirrors  a  b,  a  c,  openings  do,  eo,  to  admit  the  light  which  is  reflected 
from  the  mirrors  on  to  two  ciicnUr  apertures  r  r,  covered  with  oiled  paper,  which  are  seen  and  com¬ 
pared  when  looked  at  from  the  top  at  T  T.  The  arrows  indicate  the  direction  of  the  rays  from  the 
lamp,  and  l,  the  wax  candle  w  c.  Example-  the  distance  of  the  lights  from  the  box  being  respectively 
12  ft.  and  3  ft.  —  12  x  12  =  '44  -f  3  X  3  =  9-  Quotient,  16. 

In  the  practice  of  photometry  the  standard  used  is  a  candle  defined  by  Act 
of  Parliament  “  as  a  sperm  candle  of  six  to  the  pound,  l  urning  at  the  rate  of 
120  grains  per  hour.”  This  standard  would  be  a  very  simple  one  if  every 
candle  could  be  made  alike,  but  it  unfortunately  happens  that  the  composition 
and  the  wick  are  not  always  the  same,  and  as  important  experiments  have  to 
be  made  in  various  parts  of  the  United  Kingdom,  it  becomes  difficult  to 
assimilate  and  compare  them  with  each  other.  All  authorities  on  this  question 
have  condemned  the  use  of  test  candles.  The  credit  is  due  to  Mr.  Crookes, 
the  editor  of  the  “  Chemical  News,”  of  devising  a  standard  test  lamp-wick  and 
combustible  fluid  which  could  be  made  in  every  part  of  the  civilized  world, 
and  of  inventing  an  improved  photometer,  in  which  the  phenomena  of 
polarized  light  are  employed.  The  following  is  the  inventor’s  description  of 
the  apparatus  and  materials  used,  commencing  with  the  lamp  and  its  fuel:* 

“Alcohol  of  sp.  gr.  0.805,  and  pure  benzol  boiling  at  8l°  C.,  are  mixed 
together  in  the  proportion  of  5  volumes  of  the  former  and  1  of  the  latter. 
This  burning  fluid  can  be  accurately  imitated  from  description  at  any  future 
time  and  in  any  country,  and  if  a  lamp  could  be  devised  equally  simple  and 
invariable,  the  light  which  it  would  yield  would,  it  is  presumed,  be  invariable. 
This  difficulty  the  writer  has  attempted  to  overcome  in  the  following  manner. 


*  “  Chemical  News,  ’  July  ijth,  1868. 


THE  DIFFUSION  OF  LIGHT. 


35 


“A  glass  lamp  is  taken  of  about  2  ounces  capacity,  the  aperture  in  the  neck 
being  025  inch  diameter ;  another  aperture  at  the  side  allows  the  liquid  fuel 
to  be  introduced,  and,  by  a  well-known  laboratory  device,  the  level  of  the  fluid 
in  the  lamp  can  be  kept  uniform.  The  wick-holder  consists  of  a  platinum 
tube  r8i  in.  long,  and  o-i25  in.  internal  diameter.  The  bottom  of  this  is 
closed  with  a  flat  plug  of  platinum,  apertures  being  left  in  the  sides  to  allow 
free  access  of  spirit.  A  small  platinum  cup  0.5  in.  diameter  and  1  in.  deep 
is  soldered  round  the  outside  of  the  tube  o-5  in.  from  the  top,  answering  the 
threefold  purpose  of  keeping  the  wick-holder  at  a  proper  height  in  the  lamp, 
preventing  evaporation  of  the  liquid,  and  keeping  out  dust.  The  wick  consists 
of  52  pieces  of  hard-drawn  platinum  wire,  each  o'oi  in.  diameter  and  2  in.  long, 
perfectly  straight,  and  tightly  pushed  down  into  the  platinum-holder  until  only 
01  in.  projects  above  the  tube.  The  height  of  the  burning  fluid  in  the  lamp 
must  be  sufficient  to  cover  the  bottom  of  the  wick-holder  ;  it  answers  best  to 
keep  it  always  at  the  uniform  distance  of  175  in.  from  the  top  of  the  platinum 
wick  ;  a  slight  variation  of  level,  however,  has  not  been  found  to  influence  the 
light  to  an  extent  appreciable  by  our  present  means  of  photometry.  The  lamp 
having  the  reservoir  of  spirit  thus  arranged,  the  platinum  wires  parallel,  and 
their  projecting  ends  level,  a  light  is  applied,  and  the  flame  instantly  appears, 
forming  a  perfectly  shaped  cone  1*25  in.  in  height,  the  point  of  maximum 
brilliancy  being  0^56  in.  from  the  top  of  the  wick.  The  extremity  of  the  flame 
is  perfectly  sharp,  without  any  tendency  to  smoke  ;  without  flicker  or  move¬ 
ment  of  any  kind  ;  it  burns,  when  protected  from  currents  of  air,  at  a  uniform 
rate  of  136  gr.  of  liquid  per  hour.  The  temperature  should  be  about  60 0  F., 
although  moderate  variations  on  ither  side  exert  no  perceptible  influence. 
Bearing  in  mind  Dr.  Frankland’s  observations  on  the  direct  increase  in  the 
light  of  a  candle  with  the  atmospheric  pressure,  accurate  observations  ought 
only  to  be  taken  at  one  height  of  the  barometer  To  avoid  the  inconvenience 
and  delay  which  this  would  occasion,  a  table  of  corrections  should  be  con¬ 
structed  for  each  01  variation  of  barometric  pressure. 

“  There  is  no  doubt  that  this  flame  is  very  much  more  uniform  than  that  ot 
the  sperm  candle  sold  for  photometric  purposes.  Tested  against  a  candle, 
considerable  variations  in  relative  illuminating  power  have  been  observed  ; 
but  on  placing  two  of  these  lamps  in  opposition,  no  such  variations  have  been 
detected.  The  same  candle  has  been  used,  and  the  experiments  have  been 
repeated  at  wide  intervals,  using  all  usual  precautions  to  ensure  uniformity.” 
The  results  are  thus  shown  to  be  due  to  variations  in  the  candle,  and  not  in 
the  lamp. 

In  Arago’s  “Astronomy,”  the  author  describes  his  photometer  in  the  fol¬ 
lowing  words  : 

“  I  have  constructed  an  apparatus  by  means  of  which,  upon  operating  with 
the  polarized  image  of  a  star,  we  can  succeed  in  attenuating  its  intensity  by 
degrees  exactly  calculable  after  a  law  which  I  have  demonstrated.’”  It  is 
difficult  to  obtain  an  exact  idea  of  this  instrument  from  the  description  given  ; 
but  from  the  drawings  it  would  appear  to  be  exceedingly  complicated,  and  to 
be  different  in  principle  and  construction  from  the  oae  now  about  to  be  de¬ 
scribed.  The  present  photometer  has  this  in  common  with  that  of  Arago,  as 
well  as  with  those  described  in  1853  by  Bernard,*  and  in  1854  by  Babinet.t 


*  ••  Comptes  Rendus,’’  April  2j,  iS<3 
t  “  Proceedings  of  the  British  Association,”  Liverpool  Meeting,  1854 

3 — 2 


36 


ON  LIGHT. 


©0 
I)  c 


QQQ 

<L 


d 


that  the  phenomena  of  polarized  light  are  used  for  effecting  the  desired  end. 
But  it  is  believed  that  the  present  arrangement  is  quite  new,  and  it  certainly 
appears  to  answer  the  purpose  in  a  way  which  leaves  little  to  be  desired.  The 
instrument  will  be  better  understood  if  the  principles  on  which  it  is  based  are 
first  described. 

“  Fig.  16  shows  a  plan  of  the  arrangement  of  parts,  not  drawn  to  scale,  and 
only  to  be  regarded  as  an  outline  sketch  to  assist  in 
the  comprehension  of  general  principles.  Let  D  repre¬ 
sent  a  source  of  light.  This  may  be  a  white  disc  of 
porcelain  or  paper  illuminated  by  any  artificial  or  na¬ 
tural  light,  c  represents  a  similar  white  disc  likewise 
illuminated.  It  is  required  to  compare  the  photome¬ 
tric  intensities  of  D  and  C.  (It  is  necessary  that  neither 
I)  nor  c  should  contain  any  polarized  light,  but  that  the 
light  coming  from  them,  represented  on  each  disc  by 
the  two  lines  at  right  angles  to  each  other* forming  a 
cross,  should  be  entirely  unpolarized.)  Let  H  represent 
a  double-refracting  achromatic  prism  of  Iceland  spar; 
this  v  ill  resolve  the  disc  D  into  two  discs,  d  and  d\ 
polarized  in  opposite  directions  ;  the  plane  of  d  being, 
we  will  assume,  vertical,  and  that  of  d'  horizontal.  The 
prism  H  will  likewise  give  two  images  of  the  disc  c  ; 
the  image  c  being  polarized  horizontally,  and  c'  verti¬ 
cally.  The  size  of  the  discs  D,  c,  and  the  separating 
power  of  the  prism  H  are  to  be  so  arranged  that  the 
vertically  polarized  image  d.  and  the  horizontally  po¬ 
larized  image  c,  exactly  overlap  each  other,  forming,  as 
shown  in  the  figure,  one  compound  disc,  cd,  built  up  of 
half  the  light  from  D  and  half  that  from  C. 

“  The  measure  of  the  amount  of  free  polarization 
present  in  the  disc  c  d ,  will  give  the  relative  photome¬ 
tric  intensities  of  D  and  C. 

“  The  letter  I  represents  a  diaphragm  with  a  circular  hole  in  the  centre,  just 
large  enough  to  allow  the  compound  disc  c  d  to  be  seen,  but  cutting  off  from 
view  the  side  discs  d  d'.  In  front  of  the  aperture  in  I  is  placed  a  piece  of 
selenite  of  appropriate  thickness  for  it  to  give  a  strongly-contrasting  red  and 
green  image  under  the  influence  of  polarized  light,  k  is  a  doubly-refracting 
prism,  similar  in  all  respects  to  H,  placed  at  such  a  distance  from  the  aperturi 
in  I  that  the  two  discs  into  which  I  appears  to  be  split  up  are  separated  from 
each  other,  as  at  g  D.  If  the  disc  c  d  contains  no  j  olarized  light,  the  images 
g  r  will  be  white,  consisting  of  oppositely  polarized  rays  of  white  light  ;  but  if 
there  is  a  trace  of  polarized  light  in  c  d,  the  two  discs  g  r  will  be  coloured 
complementarity,  the  contrast  between  the  green  and  red  being  stronger  in 
proportion  to  the  quantity  of  polarized  light  in  c  d. 

“  The  action  of  this  arrangement  will  be  readily  evident.  Let  it  be  supposed 
in  the  first  place  that  the  two  sources  of  light,  D  and  C,  are  exactly  equal. 
They  will  each  be  divided  by  H  into  two  discs,  d' d  and  c  c\  and  the  two 
polarized  rays  of  which  c  d  is  compounded  will  also  be  absolutely  equal  in 
intensity,  and  will  neutralize  each  other  and  form  common  light,  no  trace  of 
free  polarization  being  present.  In  this  case  the  two  discs  of  light  g  D  will  be 
colourless.  Let  it  now  be  supposed  that  one  source  of  light  (D  for  instance) 


THE  DIFFUSION  OF  LIGHT. 


57 


is  stronger  than  the  other  (c).  It  follows  that  the  two  images  d' d  will  be 
more  luminous  than  the  two  images  c  c\  and  that  the  vertically  polarized  ray 
d  will  be  stronger  than  the  horizontally  polarized  ray  c.  The  compound 
disc  c  d  will  therefore  shine  with  partially  polarized  light,  the  amount  of  free 
polarization  being  in  exact  ratio  with  the  photometric  intensity  of  D  over  c. 

“  In  this  case  the  image  of  the  selenite  plate  in  front  of  the  aperture  I  will 
be  divided  by  K.  into  a  red  and  a  green  disc. 


is 


“Fig.  17  shows  the  instrument  fitted  up.  A  is  the  eye-piece  (shown  in 
enlarged  section  at  Fig.  3).  G  B  is  a  brass  tube,  blacked  inside,  having  a 
piece,  shown  separate  at  D  c,  slipping  into  the  end  B.  The  sloping  sides,  D  B, 
B  c,  are  covered  with  a  white  reflecting  surface  (white  paper  or  finely  ground 
porcelain),  so  that  when  D  C  is  pushed  into  the  end  B,  one  white  surface,  D  B, 
may  be  illuminated  (as  in  Fig.  17)  by  the  candle,  and  the  other  surface,  B  c,  by 
vhe  lamp.  If  the  eye-piece  A  is  removed,  the  observer,  looking  down  the  tube 
G  B,  will  see  at  the  end  a  luminous  white  disc  divided  vertically  into  two  parts, 
one  half  being  illuminated  by  the  candle  E,  and  the  other  half  by  the  lamp  F. 
By  moving  the  candle  E,  for  instance,  along  the  scale,  the  illumination  of  the 
half  n  B  can  be  varied  at  will,  the  illumination  of  the  other  half  remaining 
stationary. 

“  The  eye-piece  A  (shown  enlarged  at  Fig.  18)  will  be  understood  by  reference 
to  Fig.  16,  the  same  letters  representing  similar  parts.  At  L  is  a  lens  to  collect 
the  rays  from  B  D  C,  Fig.  17),  and  throw  the  image  into  the  proper  part  of  the 
tube.  At  M  is  another  lens,  so  adjusted  as  to  give  a  sharp  image  of  the  two 
discs  into  which  I  is  divided  by  the  prism  K.  The  part  N  Is  an  adaptation 
of  Arago’s  polarimeter  ;  it  consists  of  a  series  of  thin  plates  of  glass  capable 
of  moving  round  the  axis  of  the  tube,  and  furnished  with  a  pointer  and 
graduated  arc.  By  means  of  this  pile  it  is  possible  to  partially  polarize  the  rays 
coming  from  the  illuminated  discs  in  one  or  the  other  direction,  and  thus  bring 
to  the  neutral  state  the  partially  polarized  beam  c  d  (Fig.  16),  so  as  to  get  the 
images  g  D  free  from  colour.  It  is  so  adjusted  that  when  at  the  zero  point  it 
produces  an  equal  effect  on  both  discs. 


38 


ON  LIGHT. 


“  The  action  of  the  instrument  is  as  follows.  The  standard  lamp  being 
placed  on  one  of  the  supporting  pillars  which  slide  along  the  graduated  stem 
(Fig.  17),  it  is  adjusted  to  the  proper  height,  and 
moved  along  the  bar  to  a  convenient  distance, 
depending  on  the  intensity  of  the  light  to  be 
measured ;  the  whole  length  being  a  little  over 
4  ft.,  each  light  can  be  placed  at  a  distance  of 
24  in.  from  the  disc.  The  flame  is  then  sheltered 
from  currents  of  air  by  black  screens  placed 
round,  and  the  light  to  be  compared  is  fixed  in  a 
similar  way  on  the  other  side  of  the  instrument. 

The  whole  should  be  placed  in  a  dark  room,  or 
surrounded  with  non-reflecting  screens;  and  the 
eye  must  also  be  protected  from  direct  rays  from 
the  two  lights.  On  looking  through  the  eye-piece 
two  bright  discs  will  be  seen,  probably  of  diffe¬ 
rent  colours.  Supposing  E  represents  the  stan¬ 
dard  flame,  and  F  the  light  to  be  compared  with 
it,  the  latter  must  now  be  slid  along  the  scale 
until  the  two  discs  of  light,  seen  through  the  eye¬ 
piece,  are  about  equal  in  tint.  Equality  of  illu¬ 
mination  is  easily  obtained  ;  for,  as  the  eye  is 
observing  two  adjacent  discs  of  light,  which  pass 
rapidly  from  red-green  to  green-red ,  through  a 
neutral  point  of  no  colour,  there  is  no  difficulty 
in  hitting  this  point  with  great  precision.  It  has 
been  found  most  convenient  not  to  attempt  to  get 
absolute  equality  in  this  manner,  but  to  move  the 
flame  to  the  nearest  inch  on  one  side  or  the  other 
of  equality.  The  final  adjustment  is  now  effected 
at  the  eye-end,  by  turning  the  polarimeter  one 
way  or  the  other  up  to  450,  until  the  images  are 
seen  without  any  trace  of  colour.  This  will  be 
found  more  accurate  than  the  plan  of  relying 
entirely  on  the  alteration  of  the  distance  of  the 
flame  along  the  scale;  and,  by  a  series  of  experi¬ 
mental  adjustments,  the  value  of  every  angle  through  which  the  bundle  of 
plates  is  rotated  can  be  ascertained  once  for  all,  when  the  future  calculations 
will  present  no  difficulty.  Squaring  the  number  of  inches  between  the  flames 
and  the  centre  will  give  their  approximate  ratios ;  and  the  number  of  degrees 
the  eye-piece  rotates  will  give  the  number  to  be  added  or  subtracted  in  order 
to  obtain  the  necessary  accuracy. 

“  The  delicacy  of  the  instrument  is  very  great.  With  two  lamps,  each  about 
24  in.  from  the  centre,  it  is  easy  to  distinguish  a  movement  of  one  of  them  to 
the  extent  of  i-ioth  of  an  inch  to  or  fro  ;  and  by  using  the  polarimeter,  an 
accuracy  considerably  exceeding  that  can  be  attained. 

The  employment  of  a  photometer  of  this  kind  enables  us  to  compare 
lights  of  different  colours  with  one  another,  and  leads  to  the  solution  of  a 
problem  which,  from  the  nature  of  their  construction,  would  be  beyond  the 
powers  of  the  instruments  in  general  use.  So  long  as  the  observer,  by  the 
eye  alone,  has  to  compare  the  relative  intensities  of  two  surfaces  respectively 


THE  DIFFUSION  OF  LIGHT. 


59 


illuminated  by  the  lights  under  trial,  it  is  evident  that  unless  they  are  of  the 
same  tint  it  is  impossible  to  obtain  that  absolute  equality  of  illumination  in 
the  instrument  which  is  requisite  for  a  comparison.  By  the  unaided  eye  one 
cannot  tell  which  is  the  brighter  half  of  a  paper  disc  illuminated  on  one  side 
with  a  reddish,  and  on  the  other  with  a  yellowish  light  ;  but,  by  using  the 
above-described  photometer,  the  problem  becomes  practicable.  For  instance, 
on  reference  to  Fig.  16,  suppose  the  disc  n  were  illuminated  with  light  of  a 
reddish  colour,  and  the  disc  c  with  greenish  light,  the  polarized  discs  (T  d 
would  be  reddish,  and  the  discs  c'  c  greenish,  the  central  disc  c  d  being  of  the 
tint  formed  by  the  union  of  the  two  shades.  The  analysing  prism  K,  and  the 
selenite  disc  I,  will  detect  free  polarization  in  the  disc  c  d.  if  it  be  coloured,  as 
readily  as  if  it  were  white  ;  the  only  difference  being  that  the  two  discs  of 
light  g  r  cannot  be  brought  to  a  uniform  white  colour  when  the  lights  from 
D  and  c  are  equal  in  intensity,  but  will  assume  a  tint  similar  to  that  of  c  d. 
When  the  contrasts  of  colour  between  D  and  C  are  very  strong — when,  for 
instance,  one  is  a  bright  green  and  the  other  scarlet — there  is  some  difficulty 
in  estimating  the  exact  point  of  neutrality  ;  but  this  only  diminishes  the 
accuracy  of  the  comparison,  and  does  not  render  it  impossible,  as  it  would 
be  according  to  other  systems. 

“  No  attempt  has  been  made  in  these  experiments  to  ascertain  the  exact 
value  of  the  standard  spirit-flame  in  terms  of  the  Parliamentary  sperm  candle. 
Difficulty  was  experienced  in  getting  two  lots  of  candles  yielding  light  of 
equal  intensities;  and  when  their  flames  were  compared  between  themselves 
and  with  the  s  nrit-flame,  variations  of  as  much  as  to  per  cent,  were  some¬ 
times  observed  in  the  light  they  gave.  Two  standard  spirit-flames,  on  the 
other  hand,  seldom  showed  a  variation  of  i  per  cent.,  and  had  they  been 
more  carefully  made  they  would  not  have  varied  o  i  per  cent. 

“  This  plan  of  photometry  is  capable  of  far  more  accuracy  than  the  present 
instrument  will  give.  It  can  scarcely  be  expected  that  the  first  instrument  of 
the  kind,  roughly  made  by  an  amateur  workman,  should  possess  equal  sensi¬ 
tiveness  with  one  in  which  all  the  parts  have  been  skilfully  made  with  special 
adaptation  to  the  end  in  view.” 

Mr.  Crookes  has  shown  how  conveniently  and  accurately  his  radiometer 
(see  p.  13)  may  be  used  as  a  photometer. 

A  radiometer  will  revolve  once  in  eight  seconds  to  the  light  of  a  candle  1  ft. 
off,  whilst  24  candles  make  it  spin  with  such  velocity  as  to  become  almost 
invisible.  VVith  another  radiometer,  the  following  results  were  obtained  : 

Seconds. 

1  candle  placed  1  ft.  from  centre  of  radiometer  gave  1  revolution 

in  78  seconds  (78  x  1  =) . 7S 

2  candles  placed  1  ft.  from  centre  of  radiometer,  and  put  close 

together,  gave  1  revolution  in  39-5  seconds  (39  5  x  2  =  )  .  .  79 

2  candles  placed  opposite  to  each  other  gave  1  revolution  in  39 

seconds  (39  X  2  =  ) . 7^ 

3  candles  close  together  gave  1  revolution  in  26  5  seconds 

(26-5x3  =  )  .  .  . . .  .  79' 5 

3  candles  spread  round  the  circumference  gave  1  revolution  in 

26  seconds  (26  x  3  =  ) . 7^ 

4  candles  close  together  gave  1  revolution  in  19  seconds  (19x4  =  )  76 

5  candles  close  together  gave  1  revolution  in  16  seconds  (16  x  5=)  80 

5  candles  spread  round  the  circumference  gave  1  revolution  in 

15-5  seconds  (15  5  x  5=) . 77  5 


40 


ON  LIGHT 


Modifications  that  Light  way  undergo. 

1.  In  the  same  medium  of  the  same  density  rays  of  light  undergo  no 

change. 

2.  When  rays  of  light  pass  out  of  one  medium  into  another,  or  into  one  of 

a  different  density,  they  may  undergo  the  following  modifications  : 

3.  The  rays  of  light  may  rebound  from  the  surface  of  a  solid,  fluid,  or 

gaseous  body,  and  are  then  said  to  be  reflected,  the  rebounding  being 
denominated  Reflection. 

4.  A  ray  of  light,  after  passing  into  a  substance,  may  be  bent  from  its 

natural  course,  or  Refracted. 

5.  A  ray  of  light  may  be  split  into  two  portions  when  it  enters  certain 

bodies,  such  as  Iceland  spar,  and  each  portion  of  the  light  possesses 
distinct  properties. 

6.  A  ray  of  light  may  be  sc  checked  in  its  passage  that  a  portion  may  be 

lost  or  absorbed. 

7.  A  ray  of  light,  by  reflection,  refraction,  double  refraction,  and  absorption, 

may  acquire  new  properties,  and  become  what  is  termed  Polarized 
Light. 


THE  REFLECTION  OF  LIGHT. 

Catoptrics  is  the  name  given  to  all  effects  produced  by  reflection.  It  is  a 
word  taken  from  the  Greek  KaroirTplxos,  belonging  to  a  mirror,”  and  whilst 
the  laws  which  govern  the  reflection  of  light  are  remarkably  simple,  they  give 
rise  to  a  most  interesting  series  of  phenomena. 

Premising  that  the  incident  rays  are  those  which  fall  on  the  surface,  and 


Fig.  19. 

R  R  is  the  reflecting  sur.ace  >  A  is  is  the  incident  ray ;  B  C,  the  reflected  ray ;  A  B  P,  the  angle  of  incidence ; 

c  B  p,  the  angle  of  reflection. 

that  those  sent  off  are  cal’ed  reflected  rays,  it  is  soon  ascertained — 1st.  that 
the  incident  and  reflected  rays  always  lie  in  the  same  plane,  i.e.,  if  the 
incident  ray  falls  in  a  perpendicular  plane  or  direction,  the  reflected  one  will 
a  so  je  in  the  sam>e  plane  or  direction  ;  and  the  like  reasoning  applies  to  the 
orizontal  position.  2nd,  the  incident  and  reflected  rays  always  form  equal 


THE  REFLECTION  OF  L1CIIT. 


41 


R  R  R,  the  parallel  rays  incident  on  a  plane  or  flat  surface  at  T,  and  reflected  in  lines  at  equal  distances 
from  each  other.  The  rays  of  the  sun  are  nearly  parallel  with  each  other,  and  will  illustrate  this  fact. 


Fig.  21. 

Parallel  rays  falling  on  a  concave  mirror,  m  m,  converge  or  come  to  a  focus  or  fireplace  at  f. 

angles,  or  when  light  falls  upon  any  surface,  whether  plane  or  curved,  the 
angle  of  reflection  is  equal  to  the  angle  of  incidence. 

The  luminous  rays  may  be  parallel  to  each  other,  like  the  lines  in  a  copy¬ 
book.  or  they  may  be  divergent  when  they  spread  out  in  the  same  manner  as 
the  sticks  of  a  fan,  or  convergent  when  they  gradually  approach  each  other, 
and  end  in  a  point  like  a  spear-head. 


42 


ON  LIGHT. 


Fig  22. 

Reflection  of  parallel  rays  from  a  convex  mirror.  The  rays  which  are  reflected  become  divergent,  and 

are  shown  o:r  the  ceiling. 


A  very  large  number  of  the  waves  of  light  are  lost  when  they  fall  even  upon 
the  most  perfectly  polished  metallic  mirrors;  thus  light  reflected  from  a  clear 
and  bright  surface  of  metallic  mercury  at  an  angle  of  78°  5'  loses  nearly 
one  quarter,  and  only  754  rays  out  of  1,000  are  reflected. 

A  transparent  substance,  like  glass,  reflects  more  light  from  the  second  sur¬ 
face  than  the  first  ;  and  if  the  former  is  coated  with  an  amalgam  of  tin  and 
mercury,  the  brilliancy  of  the  reflection  of  the  second  or  coated  surface  over¬ 
powers  that  of  the  first,  although  if  a  candle  is  held  opposite  the  best  quick¬ 
silvered  mirror,  two  images  are  apparent. 

In  the  production  of  illusory  effects  by  reflection  from  the  surface  of  glass, 
the  image  reflected  from  the  surface  of  the  first  surface  interferes  with  the 
second  ;  but  this  may  be  prevented,  as  shown  to  the  author  by  a  friend,  by 
coating  the  first  side  with  a  very  delicate  film  of  collodion  or  varnish  such  as 
is  used  for  photographic  purposes.  Thus  the  intensity  of  the  reflection  of  the 
second  surface  is  increased  by  a  coating  of  amalgam,  whilst  the  intensity  of 
the  reflection  from  the  first  surface  is  reduced  by  coating  it  with  a  substance 
like  collodion,  having  an  absorptive  rather  than  a  reflecting  power  on  light. 
Where  objects  are  reflected  from  either  glass  or  silvered  glass  plane  mirrors, 
they  appear  to  come  from  the  back,  and  the  image  is  as  far  behind  the  glass 
as  the  real  object  is  before  it.  It  is  this  physical  truth  that  increases  so 
amazingly  the  effect  of  what  is  familiarly  called  “The  Ghost  Illusion.”  The 


THE  REFLECTION  OF  LIGHT 


43 


spectator  looking  at  the  image  does  not  observe  the  glass  which  has  produced 
it,  because  the  former  is  so  far  in  advance  of  the  latter.  Had  this  physical 
fact  in  catoptrics  been  remembered,  many  scientific  men  would  have  sooner 
discovered  the  secret  of  the  illusion  by  looking  in  front  of  the  image  for  the 
glass  or  reflecting  surface. 

The  great  learning  and  yet  childlike  simplicity  and  humility  of  the  illustri¬ 
ous  man  Faraday  was  never  better  shown  than  in  his  interview  with  the 
writer,  before  going  behind  the  scenes  at  the  Polytechnic  to  see  ‘how  the 
Ghost  was  done.”  Faraday  remarked,  “  Do  you  know,  Mr.  Pepper,  I  don’t 
know  how  your  pleasing  illusion  is  produced.”  Standing  in  the  pit,  and  being 
directed  to  look  upwards,  the  great  philosopher  said  he  saw  nothing  explana¬ 
tory  of  the  illusion  ;  and  it  was  only  when  the  writer  took  his  hand  and  placed 


o,  the  real  object  reflected  from  the  glass  a  b,  at  r,  to  the  eye  at  e  ;  so,  behind  the  glass,  is  where  the 
image  appears  to  come  from,  and  if  the  whole  distance  from  e  to  s  o  is  measured,  it  will  be  found 
equal  to  e  r,  k  o. 


it  on  one  of  the  great  plates  of  glass  that  he  exclaimed,  with  his  usual  enthu¬ 
siasm,  “Ah,  now  I  understand  it  !  Yes,  that  is  very  beautiful  !  ” 

The  same  truth  is  still  more  apparent  when  divergent  or  convergent  rays 
are  traced  out  in  their  reflections  from  a  plane  surface  of  glass. 

To  cause  the  image  or  ghost  to  appear,  the  lights  are  alternately  thrown  on 
or  cut  off  the  real  figure.  (See  Fig.  24,  p.  44.) 

This  mode  of  showing  the  ghost  has  to  be  modified  when  the  angles  of 
vision  are  so  different  as  seen  from  the  pit,  boxes,  and  gallery  of  a  theatre. 
Then  it  is  advisable  to  sink  a  stage  a  few  feet  below  the  regular  stage,  and  to 
arrange  a  board  at  the  same  angle  as  the  glass,  on  which  the  living  figures 
recline.  The  latter  method  allows  only  certain  movements  to  be  exhibited, 
and  is  called  the  “spectroscope”  and  “ phantoscope ”  by  travelling  showmen 
who  exhibit  the  ghost. 

One  of  the  prettiest  stories  which  can  be  illustrated  with  this  illusion  is 
that  called  “The  Knight  watching  his  Armour,”  and  as  many  persons  have 


44 


ON  LIGHT. 


seen  it  at  the  Polytechnic,  and  doubtless  might  wish  to  entertain  others  with 
this  popular  illusion  the  little  tale  is  added  as  a  sequel  to  the  contrivance 
itself. 


Fig.  24. — Exhibition  of  the  “  Ghost  ”  at  the  Polytech?iic,  being  a  section  of 

the  stage  in  the  large  Theatre. 

a,  the  real  figure  ;  b,  lime-light ;  c  c,  looking-gla^s  ;  d  d,  plate  glass  ;  g,  the  spectral  image  or  ghost, 
which  would  appear  much  farther  behind  the  glass  d  d;  s,  spectators. 


KNIGHT  WATCHING  HIS  ARMOUR. 

N.B.— ' The  spectral  image  described  appears  at  all  places  marked  with  a  star.  * 

The  following  is  told  of  a  knight,  called  Hubert  de  Burgh,  who  won  his 
spurs  on  Flodden  Field: — 

King  James  was  so  pleased  with  his  deeds  of  valour,  that  he  promised  to 
dub  him  knight  on  the  following  morning ;  but  told  him  that  he  would  have  to 
go  through  the  ancient  ordeal  of  watching  his  armour  throughout  the  previous 
night. 

Sir  Hubert  started  with  helmet  and  corselet  to  the  church.  Before  entering, 
he  met  his  lady-love,  fair  Agnes,  and  telling  her  of  his  good  fortune,  begged 
that  their  wedding  might  take  place  on  the  first  day  he  wore  his  golden  spurs. 

The  maiden  consented,  and  told  him  that  she  would  also  watch  with  him 
in  spirit  throughout  the  night,  and  bade  him  beware  of  the  many  temptations 
held  out  by  the  evil  spirits  to  all  warriors  during  the  period  of  their  watching. 

After  a  loving  farewell,  Hubert  commenced  his  duties.  And  now,  for  the 
first  time,  does  he  feel  fatigue  from  his  hard  day’s  fighting;  but  remembering 
the  caution  that  he  must  neither  eat,  drink,  nor  sleep  during  his  vigils,  he 
continues  to  watch  and  fast  until  the  break  of  morn:  sitting  down,  he  thinks 
of  his  good  fortune  in  winning  the  prize  so  much  coveted  by  all  true  warriors. 
Whilst  buried  in  thought  he  hears  the  sound  of  approaching  footsteps,  and 


THE  REFLECTION  OF  LIGHT. 


45 


Fig.  25. 


feels  that  the  time  has  come  when  he  needs  all  his  energy'  to  keep  his  armour 
pure  from  evil  touch.  On  looking  up  he  beholds  a  Benedictine  monk  *  standing 
near,  watching  him  most  carefully. 

“  Peace  be  with  you,”  says  the  monk. 

“Amen,  father,”  replies  the  knight. 

“  My  son,” continues  the  friar,  “thou  hast  acted  nobly  this  day,  and  deservest 
the  honours  our  gracious  sovereign  is  about  to  confer  on  thee;  thou  hast  had 
a  weary  day,  and  needest  rest  and  sustenance;  sleep  awhile,  and  I  will  keep 
custody  over  these  true  steel  arms.” 

“  Nay,  father,”  said  Hubert,  “  my  duty  is  to  watch,  and  not  take  deputy  for 
this  all-important  work,  neither  will  my  instructions  permit  me  to  eat  or  sleep.” 

“  My  son,”  replies  the  priest,  “  as  a  brother  of  our  holy  order,  1  absolve  thee 


46 


ON  LIGHT. 


of  this  heavy  charge,  and  will  keep  watch ;  and  in  that  same  capacity  I  bid 
thee  drink.  See !  here  is  a  cup  of  right  good  wine  which  will  much  relieve  thee.” 

“  Father,”  said  Hubert,  “sorry  am  I  that  mistrust  enters  my  mind;  I  like 
not  to  break  the  solemn  rite,  and  though  I  would  gladly  accept  thy  proffered 
gift,  I  dare  not,  without  you  make  the  sign  of  your  order  over  the  wine.” 

The  monk  for  some  time  hesitated,  but  at  length  in  an  angry  tone  replied — 

“  Fool!  drink  or  starve;  what  care  I  for  such  a  coward  loon?” 

“Now,  by  St.  Peter,”  ejaculates  Hubert,  “these  sound  not  like  a  good 
priest’s  words ;  thou  wearest  the  dress  without  the  sign  of  thy  calling.  Who 
art  thou?  Answer  quickly,  or  this  good  sword  shall  make  short  work  of  thy 
disguised  body.” 

Grasping  his  sword,  he  advances  towards  the  friar,  who,  with  a  fiendish 
laugh,  vanishes  from  before  him,  and  is  gone. 

Hubert  felt  it  must  have  been  an  evil  spirit  who  sought  to  destroy  him, 
and  with  firmer  determination  to  resist,  he  again  returns  to  his  weary  task. 
Some  time  elapsed,  when  there  comes  before  him,  gliding  out  of  the  darkness, 
a  beauteous  syren,*  who  speaks  kindly  and  fairly  to  him  of  his  great  prowess 
and  feats  of  arms.  She  tells  him  she  is  an  inhabitant  of  fairy-land— in  fact, 
their  queen — that  she  loves  him  fondly,  and  beseeches  him  to  come  to  their 
fairy  home,  where  he  shall  reign  supreme. 

She  pictures  to  him  the  delight  of  being  always  young  and  gay — of  being 
master  of  countless  hosts — flying  through  the  night  amidst  the  stars — prince 
of  all  the  land  ;  and  in  such  strains  does  she  pour  forth  her  eloquence,  that 
he  flies  with  her  in  fancy  through  the  realms  she  so  beautifully  describes  ;  but 
the  thought  of  his  fair  Agnes,  and  the  promise  made,  recalls  him  to  his  duty, 
and  slowly  advancing  towards  his  armour,  he  lays  his  hand  on  the  left  side  of 
his  corselet,  saying,  “  If  thou  be  a  spirit  of  evil,  thus  do  I  destroy  thy  charm.” 
The  temptress  gives  one  faint  sigh,  and  vanishes  from  his  view. 

Hubert,  now  relieved  from  a  second  temptation,  watches  with  renewed 
vigilance  ;  he  now  knows  that  the  morn  is  not  far  distant — -that  morn  which 
blesses  him  doubly,  by  giving  him  the  name  of  knight  and  a  fair  bride. 

The  thought  of  Agnes  causes  him  pain:  “  So  soon  shall  I  be  forced  to  leave 
her,  to  seek  a  fortune  which  I  have  not;”  and  for  the  first  time  he  knew  what 
it  was  to  wish  for  wealth.  Whilst  deep  in  thought  how  he  should  increase 
his  little  store  of  treasure,  a  stately  man,  dressed  in  the  garb  of  a  wealthy 
merchant,  stands  before  him  and  questions  him  upon  the  sadness  of  his  looks.* 
“  For  one  so  young,”  said  his  visitor,  “  should  ne’er  be  sad.” 

“  Good  sir,”  replies  Hubert,  “thou  seemest  kindly  in  thy  manner,  so  will  I 
tell  thee  of  my  only  grief.  To-morrow,  by  the  will  of  our  good  king,  I  put  on 
the  golden  spurs  of  knighthood,  I  wed  a  noble  lady,  whom  I  shall  drag  down 
to  my  own  level  of  poverty ;  though  the  world  has  given  me  an  honoured 
name,  still  do  I  lack  the  wealth  to  keep  my  wife  in  station  that  befits  her,  and 
calm  reflection  tells  me  I  did  wrong  to  take  her  promise,  and  so,  sir,  do  I 
feel  sad.” 

“  Beshrew  me,  but  thou  art  a  noble  youth,”  replies  the  merchant — “  noble 
in  thought  as  well  as  deed,  and  if  it  had  been  ordained  that  I  was  blesse 
with  such  a  son,  he  should  not  long  need  wealth.” 

“Ah !”  said  Hubert,  “fate  has  not  given  me  a  parent’s  love,  care,  or  assist¬ 
ance  ;  my  mother  died  when  1  was  yet  a  babe,  and  ere  many  months  my 
father  followed  her,  dying  as  a  noble  soldier  should,  upon  the  battle-field.” 

“  Stay,  said  the  merchant,  “  may  I  again  question  thee  as  to  whether  him 


THE  REFLECTION  OF  LIGHT. 


47 


you  spoke  of  was  the  noble  Ralph  de  Burgh,  one  of  my  most  true  and  honest 
friends  ?  ” 

“'Tis  so,”  said  Hubert,  “and  if  my  father  sought  to  win  your  friendship, 
pray  extend  the  same  good  fellowship  to  his  son.” 

“That  I  will,  right  willingly,”  returns  the  merchant.  “  Stay,”  continued  he, 
“  methinks  you  said  you  needed  gold — nay,  turn  not  away — I  have  enough, 
too  much  for  an  old  and  childless  man.  Say,  let  me  aid  thee.  I  ask  it  as 
a  favour;  nay,  I  command  it,  as  your  father's  friend.  Here, take  this  purse  to 
meet  your  most  urgent  wants,  and  to-morrow  shalt  thou  revel  in  as  great 
wealth  as  any  son  of  our  noble  houses.  Nay,  I  will  take  no  denial,” 

Hubert,  who  had  been  struggling  within  himself  as  to  his  right  to  take  the 
proffered  gift,  at  last  rises  to  approach  the  stranger,  when  he  imagines  he  hears 
sweet  music  passing  through  the  air.  He  stops  to  listen,  and  fancies  he  hears 
a  well-known  voice  exclaim,  “  Beware !  keep  to  your  trust,  ’t  is  almost  morn.” 
Amazed,  he  steps  back,  and  sees  his  fair  Agnes  beckoning  him  away,*  and 
waving  the  merchant  back,  who,  with  a  frown  and  disappointed  look,  fades 
into  the  darkness. 

The  maiden  said,  “  Dear  Hubert,  thy  task  is  finished;  for  see,  the  morn  is 
breaking.  Farewell;  we  meet  again  at  noon,  never  to  be  parted.  I  said  I 
would  watch  over  thee  in  spirit;  say,  have  I  performed  the  task?” 

As  the  warrior  is  about  to  embrace  his  beloved,  she  disappears  from  before 

him. 

The  first  tint  of  the  morning  sun  soon  glistened  upon  his  helmet ;  so  this 
true  knight  had  watched  from  eve  till  sunrise  to  guard  his  armour  from  all 
evil  spirits.  - - 

Images  formed  by  Silvered  Mirrors. 

Soon  after  the  novelty  of  “  the  Ghost”  had  waned,  another  illusion  was  pre¬ 
sented  to  the  public  called  “  Proteus  ;  or,  We  are  Here,  but  not  Here,”  the 
author  and  another  person  being  co-inventors.  A  large  and  handsome  box, 
like  a  huge  sentry-box  on  wheels,  and  raised  from  the  floor  so  that  the  spec¬ 
tators  could  see  under,  over,  and  all  round  it,  is  wheeled  on  to  the  platform 
(Fig.  26).  On  being  opened  it  appeared  to  be  well  lighted  from  the  top  by  an 
ordinary  railway  carriage  lamp,  and,  of  course,  seemed  to  be  perfectly  empty. 
The  assistant  being  now  invited  to  enter  the  box,  the  door  is  closed  and  locked, 
and,  after  a  few  minutes  have  elapsed,  is  re-opened,  when  a  skeleton  appeared 
to  be  standing  in  the  very  place  where  the  living  being  had  been  formerly 
observed  (Fig.  27.)  Again  the  door  is  closed,  and  the  next  time  it  is  opened 
the  skeleton  has  vanished,  and  the  assistant  walks  out  of  the  box  with  a  carpet 
bag.  The  person  explaining  the  apparatus  now  goes  in,  and  sounds  the  walls 
all  round  with  his  knuckles ;  and,  while  doing  this,  the  door  is  suddenly  closed, 
and  being  as  quickly  opened,  he  is  found  to  have  disappeared,  again  to  appear 
after  the  door  is  once  more  closed  and  opened.  This  illusion  is  produced  by 
two  plane  silvered  mirrors,  folding  into  the  sides  of  the  box,  and  when  open 
forming  together  an  angle  of  450.  The  mirrors  when  open  reflect  the  two  sides 
of  the  box,  and,  as  already  explained,  they  appear  behind  the  mirrors,  and 
cause  the  spectator  to  suppose  that  he  is  looking  at  an  empty  box.  In  the 
angle  formed  by  the  mirrors  the  skeleton  is  concealed  and  brought  out  when 
required,  and  in  the  same  place  the  assistant  and  lecturer  are  alternately 
hidden.  Thus  a  box  can  be  constructed  in  which  the  most  elaborate  tricks 
of  the  Davenport  Brothers  may  be  performed. 


48 


ON  LIGHT. 


In  the  accompanying  drawings,  Fig.  26  is  an  exterior,  and  Fig.  27  an  interior 
view,  and  F  ig.  28  a  horizontal  section  of  the  box  or  chamber  above  referred 
to.  The  sides  may  be  made  of  wood,  or  papier  mache,  or  sheet  iron,  but  the 
former  is  preferred. 


sides, 

found 

door. 


a  a  are  two  doors  hung  at  the  angles  of  the 
box,  and  capable  of  closing  on  the  post  d  or  of 
lying  back  in  a  recess  in  the  sides,  as  shown  on 
the  right-hand  side  of  the  box.  These  doors  a  a 
have  glass  mirrors  on  the  sides  ffff  and  a  fresco 
or  design  at  the  upper  part  of  the  box  or  chamber 
suitable  for  the  illusion  to  be  represented.  The 
post  d  is  set  at  the  junction  of  the  lines  bisecting 
the  angles  of  the  back  and  sides.  The  box  or 
chamber  as  shown  is  rectangular.  If,  for  conve¬ 
nience  or  for  the  purpose  of  any  particular  re¬ 
presentation,  the  box  or  chamber  is  desired  to  be 
wider  at  the  front  than  at  the  back,  the  post  will 
still  be  placed  at  the  junction  of  the  two  lines 
bisecting  the  angles  made  by  the  back  and  two 
but  any  considerable  departure  from  the  rectangular  form  would  be 
inconvenient,  b  is  a  door  of  clear  thick  plate  glass;  c  is  the  external 
A  lamp  is  hung  at  the  top  of  the  post  d  to  light  and  assist  in  ventilating 


THE  REFLECTION  OF  LIGHT. 


49 


the  box  by  promoting  an  upward  current,  and  a  mat  or  rug  is  placed  at  the 
bottom  of  the  box  or  chamber. 

The  same  co-inventors,  by  placing  a  silvered-glass  mirror  at  an  angle, 
and  thrown  back  from  the  spectators,  produced  some  very  popular  illusions, 
one  of  which,  called  “  The  Modern  Delphic  Oracle,”  may  be  thus  described. 
The  curtain  being  raised,  a  person  dressed  in  the  garb  of  an  ancient  Athenian 
nobleman  walks  through  and  out  of  the  entrance  to  a  temple,  across  which  a 
curtain  rolls  as  he  passes.  Walking  in  front,  he  throws  incense  on  a  brazier 
of  charcoal,  and  invokes  Socrates  to  appear.  The  curtain  now  rolls  back  and 


Elevation  showing  the  appearance  presented  by  the  illusion  called  “The  Modern  Delphic  Oracle.” 

discloses  the  head  of  the  sage  floating  in  the  air,  the  proof  of  its  solidity  being 
that  it  casts  a  shadow  on  the  wall  behind.  The  Greek  asks  Socrates  whether 
the  words  he  spoke  on  the  occasion  of  his  memorable  trial  accurately  expressed 
his  real  convictions — whether  the  purpose  of  his  life  was  as  pure  as  we  have 
been  taught  to  believe.  The  sage  replies: 

•  It  was  my  purpose  ever  to  control 
The  stormy  passions  that  perturb  tilt  soul ; 

Averse  from  idle  pomp  and  wealth,  to  find 
The  only  lasting  treasure  in  the  mind. 

The  truth  I  learned  without  reward  to  teach. 

And  show  the  falsehood  hid  by  forms  of  speech  j 
The  voice  that  warned  within  me  to  obey  — 

That  safest  guide — when  doubtful  was  my  way. 

I  learned  to  live  as  one  prepared  to  die. 

And  calmly  met  my  fate  when  death  drew  nigh  | 

Rejoiced  to  quit  this  troubled  world,  and  rest 
Immortal  in  the  regions  of  the  blest  1”  * 


*  Written  by  John  Oxenford,  Esq. 


4 


5° 


ON  LIGHT. 


The  curtain  once  more  rolls  before  the  entrance,  and  as  it  is  re-opened  to 
allow  the  Athenian  to  pass  through,  the  head  has  vanished,  and  nothing  but 
the  bare  walls  are  apparent. 

This  illusion  is  performed  with  the  aid  of  a  large  silvered  mirror,  which  is 
placed  at  an  angle  across  the  small  chamber  in  which  the  head  appears,  and 
being  perforated  in  the  centre,  the  head  of  the  actor  is  thrust  through  the 
hole,  whilst  the  rest  of  the  large  mirror  conceals  his  body,  and,  reflecting  only 
the  top  of  the  room,  painted  to  represent  the  back  of  the  temple,  induces  the 
spectator  to  suppose  he  is  looking  at  a  head  suspended  in  an  empty  room. 


Fig.  30. 

Transverse  section-  a  b,  the  silvered  mirror;  c,  the  hole  through  which  the  actor  thrusts  his  head; 
B  d,  the  ceilmg  painted  is  reflected  in  the  mirror,  and  appears  behind  the  head  at  h  h. 


The  mirror  is  carefully  supported  on  a  framework  on  wheels,  and  can  be  rolled 
out  cf  the  way  when  the  actor  representing  the  Athenian  walks  through  in 
coming  out  and  returning  to  the  temple. 

The  exhibition  of  the  Ghost  at  the  Polytechnic  took  London  by  surprise 
as  a  novelty.  It  is,  however,  evident  from  the  next  diagram,  copied  from 
“  Robinson’s  Recreative  Memoirs,”  published  in  1831,  that  he  approached 
very  near  to  the  arrangements  necessary  to  produce  reflected  images  from 
plane  surfaces.  In  the  first  place,  Robertson  remarks,  it  is  necessary  to  take 
care  that  the  angles  of  the  mirror  must  not  exceed  20°.  You  may  try  in  vain 
to  increase  this  angle  by  increasing  the  size  of  the  mirrors  rz,  b ,  c,  which  reci¬ 
procally  cause  the  rays  to  pass  through  the  opening  where  a  double-convex 
lens  is  placed.  Thus  to  obtain  an  image  of  the  same  size  as  the  object — say 
6  ft.  high — it  is  necessary  to  place  the  figure  18  ft.  distant  from  the  mirror  c, 
and  to  use  a  lens  of  9  ft.  focus,  to  have  the  image  18  ft.  on  the  other  side  of 


THE  REFLECTION  OF  LIGHT 


Fig.  31  — Robertson's  proposed  Apparatus  for  Ghost. 


the  partition,  where  it  is  projected  on  to  the  curtain  or  screen.  You  may  place 
the  real  figure  on  the  lens  side  or  the  mirror  side.  Robertson  then  gives  direc¬ 
tions  for  alter  ng  the  positions  of  the  figures,  according  to  the  space  the 
operator  has  on  either  side  of  the  partition.  It  is,  however,  difficult  to  con¬ 
ceive  that  the  image  thrown  upon  a  screen  in  this  way  could  have  been  pro¬ 
perly  illuminated,  unless  sunlight  was  employed.  The  whole  diagram  betrays 
theory  instead  of  practice. 

The  Kaleidoscope. 

One  of  the  most  philosophical  and  beautiful  instruments  ever  constructed, 
and,  like  the  above  illusion,  wholly  dependent  on  reflection,  is  the  amusing 
toy  invented  by  the  late  Sir  David  Brewster,  called  the  Kaleidoscope,  from 
the  Greek  words  kcz Aos,  beautiful,  e(8os,  a  form,  and  <tkott€m,  to  see.  Sir  David 
Brewster  says,  “  The  first  idea  of  this  instrument  presented  itself  to  me  in  the 
year  1814,  in  the  course  of  a  series  of  experiments  on  the  polarization  of  light 
by  successive  reflections  between  plates  of  glass,  which  w’ere  published  in  the 
‘Philosophical  Transactions’  for  1815, and  which  the  Royal  Society  did  me  the 
honour  to  distinguish  by  the  adjudication  of  the  Copley  medal.”  “  On  the  7th 
February,  1815,  when  I  discovered  the  development  of  the  complementary 
colours  by  the  successive  reflection  of  polarized  light  between  tw’o  plates  of 
gold  and  silver,  the  effects  of  the  kaleidoscope,  though  rudely  exhibited,  were 
again  forced  upon  my  notice.  In  repeating,  at  a  subsequent  period,  the  very 
beautiful  experiments  of  M.  Biot  on  the  action  of  homogeneous  fluids  upon 
polarized  light,  and  in  extending  them  to  other  fluids  which  he  had  not  tried, 

I  found  it  most  convenient  to  place  them  in  a  triangular  trough,  formed  by 
two  plates  of  glass  cemented  together  by  two  of  their  sides,  so  as  to  form  an 
acute  angle.  The  ends  being  closed  up  with  pieces  of  plate  glass  cemented 
to  the  other  plates,  the  trough  is  fixed  horizontally  for  the  reception  of  the 
fluids.  The  eye  being  necessarily  placed  without  the  trough,  and  at  one  end, 
some  of  the  cement,  which  had  been  pressed  through  between  the  plates  at 
the  object  end  of  the  trough,  appeared  to  be  arranged  in  a  manner  far  more 
symmetrical  and  regular  than  I  had  before  observed,  when  the  objects,  in  my 
early  experiments,  were  situated  at  a  distance  from  the  reflectors.  From  the 

4 — 2 


52 


ON  LIGHT. 


approximation  to  perfect  symmetry  which  the  figure  now  displayed,  compared 
with  the  great  deviation  from  symmetry  which  I  had  formerly  observed,  it  was 
obvious  that  the  progression  from  the  one  effect  to  the  other  must  take  place 
during  the  passage  of  the  object  from  the  one  point  to  the  other,  and  it 
became  highly  probable  that  a  position  would  be  found  where  the  symmetry 
was  mathematically  perfect. 

“  By  investigating  this  subject  optically,  I  discovered  the  leading  principles 
of  the  kaleidoscope  in  so  far  as  the  inclination  of  the  reflectors,  the  position 
of  the  object,  and  the  position  of  the  eye  are  concerned. 

“  I  found  that  in  order  to  produce  perfectly  beautiful  and  symmetrical  forms 
three  conditions  were  necessary  : 

“  Firstly,  That  the  reflectors  should  be  placed  at  an  angle  which  was  an 
even  or  an  odd  aliquot  part  of  a  circle  when  the  object  was  regular  and  simi¬ 
larly  situated  with  respect  to  both  the  mirrors ;  or  an  even  aliquot  part  of  a 
circle  when  the  object  was  irregular  and  had  any  position  whatever. 

“  Secondly,  That  out  of  an  infinite  number  of  positions  for  the  object,  both 
within  and  without  the  reflectors,  there  was  only  one  where  perfect  symmetry 
could  be  obtained,  namely,  when  the  object  was  placed  in  contact  with  the 
ends  of  the  reflectors.  This  was  precisely  the  position  of  the  cement  in  the 
preceding  experiment  with  the  triangular  trough. 

“  Thirdly,  That  out  of  an  infinite  number  of  positions  for  the  eye  there  was 
only  one  where  the  symmetry  was  perfect,  namely,  as  near  as  possible  to  the 
angular  point,  so  that  the  circular  field  could  be  distinctly  seen. 

“  The  great  step,  however,  towards  the  completion  of  the  instrument  re¬ 
mained  yet  to  be  made,  and  it  was  not  till  some  time  afterwards  that  the  idea 
occurred  to  me  of  giving  motion  to  objects ,  such  as  pieces  of  coloured  glass , 
&*c.,  which  were  either  fixed  or  placed  loosely  in  a  cell  at  the  end  of  the  instru¬ 
ment. 

“  When  this  idea  was  carried  into  execution,  and  the  reflectors  placed  in  the 
tube  and  filled  up  on  the  preceding  principle,  the  kaleidoscope  in  its  simple 
form  was  completed. 

“  When  the  kaleidoscope  was  brought  to  this  degree  of  perfection,  it  was 
impossible  not  to  perceive  that  it  would  prove  of  the  highest  service  in  all  the 
ornamental  arts,  and  would  at  the  same  time  become  a  popular  instrument  for 
the  purposes  of  rational  amusement.  With  these  views,  I  thought  it  advisable 
to  secure  the  exclusive  property  of  it  by  a  patent.  But,  in  consequence  of 
one  of  the  patent  instruments  having  been  exhibited  to  some  of  the  London 
opticians,  the  remarkable  properties  of  the  kaleidoscope  became  known  before 
any  number  of  them  could  be  prepared  for  sale. 

“According  to  the  computation  of  those  who  were  best  able  to  form  an 
opinion  on  the  subject,  no  fewer  than  200,000  instruments  were  sold  in  London 
and  Paris  during  three  months. 

“In  order  to  construct  the  kaleidoscope  in  its  most  simple  form,  we  must 
procure  two  reflectors  about  5,  6,  7,  or  8  in.  long.  These  reflectors  may  be 
either  rectangular  plates,  or  plates  shaped  like  those  in  Fig.  32,  having  their 
broadest  ends,  A  o,  B  o,  from  1  to  2  in.  wide,  and  their  narrowest  ends,  a  E, 
b  E,  half  an  inch  wide. 

“  If  the  reflectors  are  of  glass,  the  newest  plate  glass  should  be  used.  The 
plate  glass  may  be  either  quicksilvered  or  not,  and  its  posterior  surface  may  be 
ground,  or  covered  with  black  wax,  or  black  varnish,  or  anything  else  that 
reverses  its  reflecting  power. 


THE  REFLECTION  OF  LIGHT 


53 


“  The  proper  application  of  the  objects  at  the  end  of  the  reflectors  is  now 
the  only  step  which  is  required  to  complete  the  simple  kaleidoscope.  The 
most  simple  method  consists  in  bringing  the  tube  about  half  an  inch  beyond 
the  ends  of  the  reflectors.  A  circular  piece  of  thin  glass  of  the  same  diameter 
as  the  tube  is  then  pushed  into  the  tube  so  as  to  touch  the  reflectors.  The 
pieces  of  coloured  glass  being  laid  upon  this  piece  of  glass  when  the  tube  is 


Fig.  33.—  The  Oxy-hydrogen  Kaleidoscope  as  made  by  Mr.  Darker. 

Key  pattern,  produced  from  a  key. 


held  in  a  vertical  position,  another  disc,  having  its  outer  surface  ground  with 
fine  emery,  is  next  placed  above  the  glass  fragments,  being  prevented  from 
pressing  upon  them  by  a  ring  of  brass,  and  is  kept  in  its  place  by  burnishing 
down  the  end  of  the  tube.”  Such  are  the  instructions  given  by  Sir  David 
Brewster  for  the  manufacture  of  the  ordinary  kaleidoscope;  he  also  speaks  of 
the  application  of  the  instrument  to  the  magic  lantern,  but  as  the  details  were 
not  sufficiently  complete  to  enable  any  one  to  throw  the  kaleidoscopic  figure 


54 


ON  LIGHT. 


on  the  disc,  the  author  was  induced  to  urge  Mr.  Darker,  of  Paradise  Street, 
Lambeth,  to  persevere  in  the  adjustment  of  the  mirrors,  lenses,  and  lighting 
until  perfection  was  obtained.  During  the  Christmas  of  1866  the  oxy-hvdrogen 
kaleidoscope  was  exhibited  daily  at  the  Polytechnic  with  the  greatest  success, 
and  by  its  means  the  principle  of  the  instrument  could  be  better  understood. 


Fig.  34. 

a.  Figures  obtained  bv  putting  a  single  figure,  such  as  key,  into  the  apparatus;  b,  c,  other  figures 
produced  by  using  the  light  only  with  an  empty  slide. 


It  is  chiefly  by  the  adjustment  of  the  light  that  the  original  angular  opening 
is  gradually  multiplied  by  reflection  eight  times,  and  eight  distinct  sectors 
or  divisions  become  visible  on  the  disc.  When  the  tip  of  the  finger  is  now 
inserted,  eight  single  reflections  or  four  double  ones  are  the  result,  and  by 
thrusting  in  all  the  fingers  the  curious  figures  shown  at  *>,  Fig.  35,  are  obtained. 

Not  only  are  transparent  bodies,  such  as  glass,  exhibited  with  success, but  any 
opaque  object  will  produce  the  most  distinct  and  symmetrical  figures  on  the 


Fig.  35. 

Figures  obtained  on  the  screen  from  the  oxy-hydrogen  kaleidoscope  with  pins  and  needles.  D;  the 

fingers,  e;  and  f,  a  comb. 


screen ;  in  Fig.  35  the  pattern  c/is  chiefly  produced  with  a  cell  containing  only 
pins  and  needles.  If  glass  be  used,  it  should  always  be  broken  from  coloured 
glass  rods  with  the  hammer,  in  order  to  secure  the  conchoidal  fracture,  as  the 
wedge-shaped  figures  give  gradual  tones  of  colour,  which  are  very  pleasing  to 
the  eye,  and  produce  fair  imitations  of  the  colours  and  grouping  of  rubies, 
emeralds,  and  sapphires  when  projected  on  the  screen. 


THE  REFLECTION  OF  LIGHT. 


55 


A  jentleman,  who  saw  these  and  other  patterns,  and  especially  some  obtained 
by  using  ferns  and  other  natural  objects,  was  so  pleased  that  he  stated  it  was 
his  intention  to  have  an  oxy-hydrogen  kaleidoscope  fitted  up  in  his  calico- 
printing  establishment,  in  order  to  assist  the  artist  who  designed  the  patterns; 
and  he  stated  that,  although  they  had  long  used  the  ordinary  kaleidoscope  for 
this  purpose,  the  oxy-hydrogen  one  gave  a  much  better  notion  of  the  effect 
required  to  be  produced,  and  would  enable  the  manufacturer  to  select  and 
decide  upon  the  best  patterns  for  commercial  purposes. 

The  phenomena  of  light  produced  by  reflection,  and  the  instruments  which 
have  been  constructed  to  demonstrate  these  effects,  are  too  numerous  to  be 
detailed  here,  so  that  two  or  three  examples  must  suffice.  The  property  of 
reflection  is  affected  more  by  the  condition  of  the  surface  than  by  the  physical 
nature  of  the  substance  used  as  a  reflector.  The  kaleidoscope  reflectors  em¬ 
ployed  by  Mr.  Darker  are  made  of  the  best  plate  glass,  coated  with  metallic 
silver,  or,  better  still,  platinum,  and  it  is  extremely  difficult  to  prevent  a  slight 
deposit  of  moisture  upon  them.  The  watery  particles  greatly  impair  the 
kaleidoscopic  figures,  and  demonstrate  how  thoroughly  the  power  of  reflection 
dep  nds  on  the  state  of  the  surface,  as  this  exquisitely  thin  film  of  moisture 
interferes  with  the  perfect  illumination  of  the  kaleidoscopic  figure.  By  a 
simple  arrangement  of  the  tube  containing  the  focussing  lens,  air  is  pumped 
through  and  over  the  mirrors,  and  by  this  means  the  moisture  deposited  may 
be  quickly  removed. 


Thf.  Japanese  Magic  Mirror. 

Some  mirrors  made  in  Japan  have  a  very  curious  property.  The  back  is 
usually  ornamented  with  Japanese  characters,  also  with  flowers,  vases,  &c. ; 
the  front  is  polished  in  the  usual  manner,  like  any  other  metallic  speculum, 
and.  if  carefully  examined,  with  or  without  a  magnifying  power,  betrays  nothing 
more  than  the  highly  polished  surface  of  the  alloy,  which  appears  to  be  com¬ 
posed  chiefly  of  tin  and  copper.  When,  however,  the  mirror  is  held  in  the 
highly  divergent  rays  emitted  from  an  oxy-hydrogen  light,  it  not  only  reflects 
on  to  a  disc  the  surface  of  the  polished  disc,  but  likewise  all  the  Japanese 
characters,  vases,  and  flowers,  which  are  in  relievo  on  the  back  of  the  mirror. 


Fig.  37. — Reflection  from  the  front  or  bright  side  of  the  Japanese  Mirror. 


We  have  in  the  above  experiment  a  scientific  puzzle  that  is  somewhat  difficult 
to  explain.  May  it  be  supposed  that  much  of  the  success  of  the  effect  obtained 
is  due  to  the  nature  of  the  alloy  used  in  the  casting  of  the  mirror  ?  The 
figures  in  relief  on  the  back  of  the  mirror,  during  the  operation  of  casting, 
must  first  enter  the  mould  in  the  liquid  state :  are  these  first  and  quickly 
congealed  before  the  whole  mass  of  metal  ?  and  does  the  minute  difference  in 
the  molecular  condition  of  the  metal  produced  by  a  greater  rapidity  of  cooling, 
extend  through  the  thin  metal  to  the  front  and  polished  side? 

Would  careful  heating  and  annealing  destroy  the  effect  ?  Whatever  may 
be  the  method  employed,  it  is  certain  that  the  figures  reflected  from  the 
surface  are  wholly  invisible,  and  cannot  be  observed  in  the  strongest  light, 
and  with  a  good  magnifying-glass.  In  all  cases  where  metals  are  inlaid  with 
other  metals  the  lines  where  the  metals  join  are  distinctly  visible,  and  there¬ 
fore  it  cannot  be  supposed  that  the  Japanese  mirror  is  made  in  this  manner. 
Are  the  mirrors  cast  in  a  double  mould,  one  side  of  which  is  in  intaglio  and 
the  other  in  relievo ,  and  after  being  cast  do  they  grind  down  the  sides  of  the 
mirror  in  which  the  figures  are  sunk;  until  they  get  a  plain  surface,  which  is 
then  polished,  leaving  the  other  side  and  back  of  the  mirror  with  the  figures 
in  relief?  The  pattern  die,  conferred  on  both  sides  of  the  metal  whilst  soli- 


THE  REFLECTION  OF  LIGHT. 


57 


difying,  might  still  further  determine  the  molecular  difference.  It  is  a  curious 
circumstance  that  the  Chinese  mirrors,  made  in  imitation  of  the  Japanese 
mirrors,  do  not  answer  the  purpose,  the  former  being  much  heavier  than  the 
latter.  Whatever  may  be  the  secret  of  success,  it  is  certain  that  this  is  only 
another  instance  of  the  remarkable  ingenuity  of  the  Japanese  workers  in 
metal. 

Sir  D.  Brewster  explains  the  apparent  anomaly  by  suggesting  that  the 
design  on  the  back  is  dexterously  reproduced  by  careful  engraving,  which  is 
so  lightly  done  that  the  figures  traced  are  quite  invisible  after  the  mirror  is 
brought  to  the  highest  degree  of  polish,  and  it  is  only  by  submitting  the 
mirror  to  a  powerful  light,  and  casting  the  reflection  of  the  surface  on  a  wall, 
that  the  design  becomes  apparent.  The  concealment  of  the  most  delicate 
engraving,  unless  done  in  some  way  by  Barton’s  ruling-machine,  would  be 
extremely  difficult,  if  not  impossible.  The  Japanese  know  nothing  of  the 
machine  with  which  Barton  ruled  his  steel  patterns,  and  even  if  they  did  the 
reflected  patterns  would  give  evidence  of  colour,  which  is  not  the  case. 

In  the  “Journal  of  the  Asiatic  Society,”  vol.  i.,  page  242,  there  is  a  very 
clever  paper,  by  James  Prinseps,  on  “  The  Magic  Mirrors  of  Japan.”  He  says: 

“  The  Japanese  mirror  is  a  slightly  convex  disc  of  bell  metal,  about  6  in.  in 
diameter,  and  a  quarter  of  an  inch  in  thickness  on  the  edge,  ground  and  po¬ 
lished  on  the  convex  face,  and  covered  with  a  thin  coating  of  silver  to  give  it  a 
white  colour.  (Fig.  38,  p.  39.) 

“  The  back  of  the  mirror  is  deeply  curved  or  indented,  with  ornamental  work 
in  circles  and  festoons,  and  it  bears  an  inscription  in  the  Japanese  character 
in  high  relief  upon  what  may  be  termed  the  tympanum  of  the  disc ;  in  the 
centre  there  is  a  projecting  knob,  perforated  laterally  to  receive  a  string  for 
suspending  the  mirror.  The  metal  is  highly  sonorous  when  struck  as  a  bell, 
and  is  so  soft  as  easily  to  be  indented  or  scratched  on  contact  with  any  hard 
substance.  I  found  its  composition  to  be 

Copper  80 
Tin  20 


100 

with  no  traces  ot  silver  or  arsenic,  and  a  very  slight  indication  of  zinc.” 

Mr.  Prinseps  then  describes  the  curious  property  of  the  mirror,  similar  in 
effect  to  those  already  mentioned  and  illustrated  at  Fig.  37,  p.  36.  He  then 
proceeds  to  discuss  the  cause  of  this  seeming  anomaly. 

“  It  then  occurred  that  the  various  parts  of  the  Japanese  mirror  might  be  of 
different  density ,  supposing  the  pattern  to  be  made  by  stamping,  and  that 
either  the  rays  of  light  might  be  more  forcibly  repelled  by  the  denser  metal 
than  by  the  lighter,  or  that  parts  of  the  surface  would  acquire  different 
degrees  of  polish,  sufficient  to  cause  the  illusion,  although  imperceptible  to  the 
eye.  But  in  such  case  the  thin  parts,  from  being  the  hardest,  should  give  the 
stronger  reflection. 

“  This  supposition  was  also  overthrown  by  experiment.  A  disc  of  silver, 
having  been  annealed  at  a  red  heat  so  as  to  be  quite  soft,  was  stamped  on  the 
back  with  a  circular  ring,  deeply  indented,  so  as  to  harden  ihe  silver  in  that 
part  only.  The  opposite  surface  was  then  ground  and  polished,  when  it  was 
found  to  give  a  clear  and  uniformly  reflected  spectrum. 

“Another  and,  I  believe,  the  true  explanation  is  suggested  by  the  well-kno'vn 


58 


ON  LIGHT. 


phenomenon  of  the  reflection  from  a  brass  button,  which  every  school-boy  has 
remarked  when  sporting  his  Sunday  ‘  blue  coat  with  metal  buttons’  in  the  sun¬ 
shine  of  his  tutor’s  parlour-window.  The  button  throws  a  radiated  irregular 
image  on  the  wall,  exhibiting  two  bright  concentric  circles,  one  on  the  edge  and 
another  about  one-third  within  it,  and  there  is  generally  a  bright  spot  in  the 
centre  :  all  of  this  seems  but  the  picture  of  the  stamp  on  the  back  of  the  button : 
the  radii  resemble,  and  indeed  coincide  with,  the  letters  of  ‘superfine’  or  ‘trebly 
gilt  ’  inscribed  within  a  double  circle,  and  the  central  spot  represents  the 
shank.  There  can  be  little  doubt  that  the  principle  is  in  this  case  precisely 
that  of  the  Japanese  mirror;  and,  on  a  cursory  view,  the  surface  looks  equally 
smooth  and  unsuspicious.  On  minute  examination,  however,  of  several  buttons, 

I  found  them  to  be  by  no  means  plane ;  their  general  surface  is  slightly  convex; 
there  is  a  hollow  in  the  centre  and  a  projection  in  the  position  of  the  inscrip¬ 
tion  behind,  caused  no  doubt  by  the  blow  necessary  in  stamping  it.  The  polish 
is  probably  given  by  a  rotary  motion,  and  consequently  does  not  remove  these 
very  small  irregularities.  To  follow  up  the  experimental  investigation,  I  selected 
one  of  the  buttons  which  gave  a  good  image,  ground  it  on  a  flat  hone,  and 
polished  it:  all  of  the  magical  figures  vanished  in  a  moment,  and  a  plain, 
bright  disc  appeared  in  their  stead.  Here,  then,  may  be  a  key  to  the  mystery 
of  the  mirror:  the  deception  is  entirely  produced  by  irregularities  on  the  sur¬ 
face,  which  are  rendered  the  less  perceptible  to  the  eye  because  the  surface  is 
convex  instead  of  being  plane.  But  it  may  be  objected  that  the  two  circles 
which  appear  bright  in  the  reflected  spectrum  of  the  button  represent  the 
indented  or  thin  parts  of  the  metal,  whereas  the  thick  parts  ot  the  Japanese 
mirror  are  those  which  will  appear  illuminated.  A  short  analysis  of  the  facts 
in  either  case  will  readily  explain  to  what  these  discrepancies  are  attributable; 
but  it  will  be  necessary  to  have  recourse  to  a  diagram.' 

“  Let  A  B,  Fig.  38,  be  a  plain  mirror  upon  which  the  rays  of  light  R  impinge; 
they  will  be  reflected  uniformly  to  R',  forming  a  clear  image.  Now  let  A  B  C  D 
E  F  G  be  another  reflecting  surface,  having  two  convexities,  B  C,  E  F,  and  one 
concavity  in  the  centre  D  (the  condition  nearly  of  the  brass  button).  In  this 
case  the  light  reflected  from  the  outer  concave  flexures  of  the  protruding 
portion  of  the  surfaces  B  c,  E  F,  will  converge  in  the  foci  b  c  and  e /respectively, 
at  distances  corresponding  to  the  radius  of  their  curvature;  the  effect  will,  of 
course,  be  visible  within  wide  limits  of  the  actual  focus.  In  most  of  the  buttons, 
however,  the  central  depression  is  so  great  that  it  collects  the  rays  in  a  focus, 
/  a  few  inches  only  in  front  of  the  surface ;  and  when  the  spectrum  is  thrown 
farther  off,  the  rays  crossing  from  two  less  distinct  luminous  foci,  d' d',  it  follows 
from  analogy  that  the  thin  parts  or  tympanum  of  the  Japanese  mirror  are 
slightly  convex  with  reference  to  the  rest  of  the  reflecting  surface,  which  may 
have  been  caused  either  by  the  ornamental  work  being  stamped  or  partially 
carved  with  the  hammer  and  chisel  on  its  back,  or,  what  is  more  probable, 
that  part  of  the  metal  was  by  this  stamping  rendered  harder,  so  that  in  po¬ 
lishing  it  was  not  worn  away  to  the  same  extent.” 

Since  the  above  was  written,  an  English  brass-finisher  appears  to  have  dis¬ 
covered  the  secret.  Taking  ordinary  brass,  he  finds  that  any  figure  stamped 
upon  it  with  a  proper  die,  and  ground  down  and  polished,  will  not  reflect  the 
figure  impressed  by  the  die;  but  if  the  process  with  the  same  die  is  repeated 
three  times ,  so  that  the  figure  intended  to  be  projected  from  the  surface  is 
stamped  three  times  in  the  same  place,  and  subsequently  ground  down  and 
polished  after  each  stamping,  then  a  molecular  difference  is  established  between 


THE  REFLECTION  OF  LIGHT 


59 


Fig.  38. 


the  stamped  and  unstamped  parts,  which  is  not  apparent  to  the  eye,  but  is 
shown  directly  the  surface  so  acted  on  is  used  for  reflecting  light. 

There  can  be  no  doubt  that,  until  the  magic  lantern  was  invented,  the  only 
optical  apparatus  used  by  persons  who  pretended  to  wield  the  “  magic  art  ” 
consisted  of  plane  and  concave  mirrors.  The  memoirs  of  Monsieur  E.  J. 
Robertson,  published  in  Paris  in  1831,  disclose  some  amusing  applications  of 
surfaces  that  reflect  light,  and  he  describes  how  the  magician  Nostrodamus 
deceived  the  politic  Marie  de  Medicis,  and  pretended  to  show  the  astute 
queen  the  king  for  whom  the  throne  of  the  Bourbons  was  destined.  He  states 
that  Marie  de  Medicis,  disquieted. by  apprehensions  regarding  the  succession 
to  the  throne  of  France,  went  to  consult  Nostrodamus.  This  dealer  in 
miracles  by  the  use  of  plain  mirrors  produced  the  effect  shown  in  Fig.  39,  p.  40, 

La  Boite  Magique. — The  magic  box  is  another  amusing  example  of  the 
same  kind,  only  in  this  case  a  concave  mirror  is  employed  instead  of  a  plane 
one.  This  experiment,  Robertson  declares,  is  charming,  and  having,  he  says, 
told  a  lady  the  secret  of  several  illusions  which  pleased  her  greatly,  he 
happened  to  be  staying  with  the  same  individual  in  the  country,  at  the  time 
that  a  most  agreeable  gentleman  was  paying  his  court  to  her;  the  latter 
said  to  her  lover,  “  If  you  do  not  fear  apparitions,  1  promise  you  one  this 
evening  which  may  please  you.  At  twelve  precisely  open  the  box  that  you 


6o 


ON  LIGHT. 


Fig.  39. 

The  throne,  placed  in  the  first  apartment  a,  is  reflected  by  a  mirror  concealed  in  the  canopy  b,  Marie  de 
Medicis  beholds  the  representation  of  the  image  in  a  mirror  c,  supported  by  a  Cupid. 


will  find  on  your  table,  of  which  this  is 
the  key,  and  my  image  will  come  out 
of  the  box.”  This  promise  seemed  only 
an  agreeable  kind  of  banter  to  her  gal¬ 
lant,  and,  though  he  promised  to  open 
the  box,  he  feared  to  do  so,  lest  he  might 
be  made  the  dupe  of  some  trick.  At 
first  he  would  not  touch  it,  but  at  last, 
yielding  to  curiosity,  he  opened  the 
box,  when  the  image  of  his  lady-love 
immediately  appeared,  with  a  very  grave 
and  composed  air  ;  but  she,  guessing 
that  the  countenance  of  her  gallant 
must  bear  a  strange  —  a  serio-comic, 
though  interesting — expression,  forgot 
that  silence  was  necessary,  and,  burst¬ 
ing  out  into  laughter,  was  thus  disco¬ 
vered  in  the  adjoining  room. 


A,  concave  mirror;  the  head  b,  inclined  towards  c,  appears  to  emerge  from  D,  to  an  eye  placed 
at  e;  the  head,  b,  must  be  well  illuminated,  and  the  mirror  in  the  shadow,  so  that  it  may  not  be 
visible;  g  is  the  wall;  at  h  a  box  to  open,  firmly  fixed  on  a  table  k.  The  interior  of  the  box  is  painted 
black,  and  of  course  the  wall  which  separates  the  two  apartments  is  open  under  the  table. 


THE  REFLECTION  OE  LIGHT. 


61 


The  ancients  made  use  of  concave  minors  to  rekindle  the  vestal  fires. 
Plutarch  says  they  employed  a-Kapua,  or  dishes,  for  that  purpose.  They  were, 
most  likely,  hemispherical  vessels  highly  polished  within. 

As  an  illustration  of  the  more  refined  uses  and  applications  of  silvered 
mirrors,  may  be  quoted  the  admirable  instructions  given  by  Mr.  John  Browning, 
of  iii  Minories,  for  adjusting  and  using  reflectors  for  astronomical  tele¬ 
scopes  with  silvercd-glass  specula. 


Fig.  41 


Mr.  Browning’s  Description  of  the  Silvered  Glass  Reflecting 

Telescopes. 

These  telescopes  are  of  the  kind  called  Newtonian,  a  form  so  well  known, 
that  it  is,  perhaps,  scarcely  necessary  to  describe  it  ;  but  I  append  a  plain 
diagram  (Fig.  41)  and  brief  description,  because  it  will  assist  in  making 
clearer  the  instructions  I  have  given  further  on,  of  the  method  of  adjusting 
the  instrument.  The  Newtonian  telescope  consists  of  a  tube  closed  at  the 
lower  end,  which  is  occupied  by  a  concave  mirror,  M.  The  cone  of  rays 
reflected  from  this  mirror  is  again  reflected  at  right  angles  from  the  surface 
of  a  small  plane  mirror,  m  n,  mounted  at  an  angle  of  45°  near  the  open  end 
of  the  tube,  into  the  eye-piece,  which  is  exactly  opposite.* 

In  reflecting  telescopes,  as  originally  constructed,  the  concave  mirror  was 
made  of  an  extremely  hard  alloy,  known  as  speculum  metal.  These  metallic 
mirrors  possessed  several  disadvantages,  so  serious  in  character  that  they 
have  for  some  time  fallen  out  of  general  use.  The  principal  defects  were 
the  following : 

1.  From  the  extreme  brittleness  of  the  alloy,  they  were  very  liable  to  fracture, 
sometimes  breaking  merely  from  a  sudden  change  of  temperature. 

2.  From  their  great  weight  it  was  extremely  difficult  to  mount  them  in 
such  a  way  as  to  prevent  flexure,  the  smallest  amount  of  which  greatly 
injured  their  optical  performance. 

3.  Their  greatest  drawback,  however,  consisted  in  the  fact  that  the  surface 
of  the  metal,  from  damp  or  other  causes,  sometimes  became  very  rapidly 
tarnished,  and  this  tarnish  could  seldom  be  removed,  except  by  repolishing 
and,  consequently,  refiguring  the  mirror  ;  and  this  involved  nearly  as  great 
an  outlay  as  the  purchase  of  a  new  speculum,  besides  incurring  the  serious 
risk  of  a  fine  figure  being  irretrievably  lost. 

In  the  telescope  now  described,  the  metallic  mirror  is  replaced  by  one  of 


*  The  mirror  must  not  be  worked  to  a  spherical,  blit  to  a  rery  perfect  parabolic  curve. 


62 


ON  LIGHT. 


glass,  on  the  surface  of  which  a  coating  of  pure  silver  has  been  deposited  by 
Liebig’s  process,  and  described  further  on. 

These  glass  mirrors  are  not  at  all  injuriously  affected  by  change  of  tem¬ 
perature,  and  their  lightness  very  considerably  reduces  their  liability  to  flexure ; 
indeed,  mounted  in  the  manner  I  shall  presently  describe,  no  flexure  has  ever 
been  observed  in  them.  I  may,  however,  state  that  1  make  the  discs  of  the 
specula,  which  Mr.  With  parabolizes  for  me,  out  of  glass  nearly  twice  the 
substance  of  that  generally  used  for  the  purpose.  The  coating  of  pure  silver 
reflects  fully  one-third  more  light  than  the  best  speculum  metal,  as  the  alloy 
before  mentioned  is  called.  But  the  greatest  superiority  of  silvered  glass  over 
metallic  mirrors  consists  in  the  fact  that,  should  they  become  tarnished,  their 
brilliancy  may  readily  be  restored  by  gentle  friction  with  soft  leather  and  a 
little  of  the  finest  rouge ;  and  even  should  the  silver  coating  become  utterly 
spoiled,  it  may  be  easily  removed  without  in  any  way  impairing  either  the 
figure  or  polish  of  the  glass  speculum,  and  a  fresh  one  deposited  at  a  trifling 
cost,  thus  making  the  mirror  equal  to  new ;  and  this  may  be  repeated  indefi¬ 
nitely.  Should  the  owner  possess  a  little  patience,  he  may  renew  the  coating 
himself  at  the  cost  of  only  a  few  pence.  The  silvering  process  is  fully  described 
further  on. 

With  this  alteration  these  telescopes  have  latterly  gained  much  ground  in  the 
opinion  of  practical  observers  well  known  in  the  scientific  world,  who  have 
had  considerable  experience  in  working  with  them. 

On  figuring  Specula. — About  three  years  since,  the  Rev.  Cooper  Key  dis¬ 
covered  a  more  simple  method  of  parabolizing  the  surface  of  specula  than  any 
which  had  hitherto  been  employed,  and  by  this  process  he  produced  two  fine 
specula  of  12  in.  diameter. 

The  process  by  which  these  specula  were  worked  Mr.  Key  communicated  to 
Mr.  G.  With,  and  after  having  worked  by  Mr.  Key’s  process  until  a  few  months 
since,  Mr.  With  at  length  contrived  another  plan  of  working,  by  which  he 
considers  still  finer  results  are  with  greater  certainty  secured. 

The  wonderful  perfection  of  Mr.  With’s  specula  is  now  generally  admitted, 
and  it  is  almost  certain  that  they  surpass  any  that  have  previously  been 
produced.  1  have  great  pleasure  in  stating  that  specula  of  great  excellence 
can  be  obtained  at  moderate  cost. 

On  mounting  Specula. — It  has  elsewhere  been  suggested  that  much  of  the 
dissatisfaction  which  has  been  expressed  by  those  who  have  used  reflectors 
has  arisen  from  their  having  been  imperfectly  mounted. 

Because  specula  are  much  cheaper  than  achromatic  object-glasses,  it  has  _ 
been  supposed  that  they  could  be  mounted  at  proportionately  less  cost  than 
that  incurred  in  mounting  reflectors.  This  is  only  true  to  the  extent  that  cost 
can  be  saved  by  reason  of  their  shorter  focal  length. 

It  cannot  be  too  strongly  enforced  that,  to  give  the  best  performance, 
reflectors  require  to  be  mounted  more  steadily  than  refractors,  because  by  a 
well-known  law  of  optics  the  effect  of  any  vibration  will  be  multiplied  many 
times.  Their  tubes  must  also  be  carefully  arranged,  so  as  to  avoid  as  much 
as  possible  the  interference  of  air-currents,  which  are  the  bane  of  reflectors 
improperly  mounted  or  badly  situated.  The  specula  in  the  telescopes  now 
described  are  mounted  rigidly  on  a  new  plan,  which  ensures  permanence  in 
adjustment  and  prevents  flexure.  This  plan  is  represented  in  Fig.  42. 

The  bottom  of  the  speculum  A  is  a  carefully  prepared  plane  surface,  and 
the  bottom  of  the  inner  iron  cell  B,  on  which  it  rests,  is  also  a  plane.  The 


THE  REFLECTION  OF  LIGHT. 


63 


c 


G 


F  re.  42. 


speculum  is  clamped  in  this  cell  by  the  ring  G  G,  and  it  may  be  removed  from 
and  replaced  in  the  telescope  without  altering  its  adjustment.  The  elastic 
methods  of  mounting  the  speculum,  which  have  hitherto  been  emploved, 
generally  required  re-adjustment  whenever  the  speculum  had  been  removed. 
The  reflecting  diagonal  prism  or  mirror  is  mounted  in  the  manner  shown 
in  the  diagrams  Figs.  43  and  44. 


c. 


c 


r 


Fig.  44. 


Fig.  43 


In  these  B  B  B  represent  strips  of  strong  chronometer  spring  steel,  placed 
edgewise  towards  the  speculum,  by  which  the  prism  or  small  mirror  D  is 

suspended.  . 

The  mirror,  thus  mounted,  does  not  produce  such  coarse  rays  on  bright 
stars  as  when  it  is  fixed  to  a  single  stout  arm ;  it  is  also  less  liable  to  vibration, 
which  is  very  injurious  to  distinct  vision,  or  to  flexure,  which  interferes  with 
the  accuracy  of  the  adjustments. 

If  an  observer  determines  to  lay  out  a  given  sum  in  the  purchase  of  a  tele¬ 
scope,  he  will  find  it  to  his  advantage  to  have  a  smaller  speculum  completely 
mounted,  instead  of  a  large  speculum  imperfectly  mounted.  With  the  smaller 
and  perfect  instrument  he  will  really  do  more  work,  and  with  much  greater 
comfort  and  satisfaction  to  himself.  No  matter  how  good  a  speculum  may 
be,  nothing  can  be  told  of  its  performance  on  difficult  double  stars  if  it  is 
mounted  on  an  unsteady  stand. 


64 


ON  LIGHT. 


t  {Je5J1t'azimut.h  s*and>  represented  m  Fig.  45,  is  entirely  of  iron.  The  tube 
of  the  telescope  is  of  extremely  stout  block  tin,  coloured  dark  green,  the  stand 
being  coloured  dark  chocolate.  The  body  is  equipoised,  so  that  it  will  remain 
in  any  position,  while  the  movements  are  so  smooth,  and  the  leverage  so 
arranged,  that  a  star  may  be  followed,  even  with  a  power  of  300,  without  -crew 
motions.  The  instrument  can  be  used  on  a  table,  at  any  window ;  and  a  stand 
is  supplied  with  it,  on  which  it  can  be  supported  at  a  convenient  height  when 
it  is  used  in  the  open  a  r.  This  mounting  is  only  adapted  for  a  small-sized 
speculum,  say  not  exceeding  5  in.  in  diameter,  as,  if  made  of  a  larger  size,  it 


hlG.  45. —  The  small  Alt-azimutk. 


would  be  so  heavy  as  not  to  be  portable;  while  with  higher  powers  than  300 
such  as  specula  of  6  in.  and  above  will  easily  bear,  the  celestial  bodies  cannot 
be  followed  without  screw  motions.  By  fastening  the  circular  foot  down  on  a 
block  of  wood  of  a  wedge  form,  the  angle  being  the  complementary  angle  to  the 
latitude  of  the  place,  this  stand  can  very  readily,  and  at  a  comparatively  trifling 
expense,  be  made  to  move  equatorially,  so  that  the  heavenly  bodies  can  be 
followed  with  a  single  motion  of  the  telescope.  Such  an  arrangement  is  shown 
m  fig.  45.  A  cheaper  mounting  is  shown  in  Fig.  54. 

divide  ^dn(dl  silvcred-glass  speculum,  with  powers  from  100  to  150,  will 

P  Orionis.  a  Lyras. 

S  Geminorum.  e  Hydrae. 

£  Ursae  Majoris. 

c  Bootis. 

v  Ceti.  e  Dracoms. 


The  6 1  will  divide,  with  powers  from  200  to  300 — 

e  Arietis.  a  Herculis. 

£  Bootis.  32  Orionis. 

1  Equulei.  rj  Coronae  Borealis. 
36  Andromedae. 


1  he  8J,  with  powers 
divide — 


from  300  to  35°)  a  favourable  state  of  the  air,  will 


THE  REFLECTION  OF  LIGHT. 


6.5 


7 

r 


3  Andromedas. 
Bootis. 


These  last-named  double  stars  are  both  under  half  a  second  apart,  and  are 
so  difficult  to  divide  as  to  have  hitherto  been  considered  good  work  for  a 
12-inch  speculum. 

TO  SILVER  GLASS  SPECULA. 

Prepare  three  standard  solutions  - 
Solution  A  i  Crystals  of  nitrate  of  silver 


Solution  B 


Solution  C 


90  grains  \ 

4  ounces  \ 
1  ounce  ) 

25  ounces  f 
^  ounce  ) 

5  ounces 


Dissolve. 


Dissolve. 

Dissolve. 


Distilled  water 
Potassa,  pure  by  alcohol 
Distilled  water  . 

\  Milk-sugar,  in  powder 
\  Distilled  water  . 

Solutions  A  and  B  will  keep,  in  stoppered  bottles,  for  any  length  of  time; 
solution  C  must  be  fresh. 

The  Silvering  Fluid. — To  prepare  sufficient  for  silvering  an  8-inch  speculum, 
pour  2  ounces  of  solution  A  into  a  glass  vessel  capable  of  holding  35  fluid 
ounces.  Add,  drop  by  drop,  stirring  all  the  time  with  a  glass  rod,  as  much  liquid 
ammonia  as  is  just  necessary  to  obtain  a  clear  solution  of  the  grey  precipitate 
first  thrown  down.  Add  4  ounces  of  solution  B.  The  brown-black  precipi¬ 
tate  formed  must  be  just  re-dissolved  by  the  addition  of  more  ammonia  as 
before.  Add  distilled  water  until  the  bulk  reaches  1 5  ounces,  and  add,  drop 
by  drop,  some  of  solution  A,  until  a  grey  precipitate,  which  does  not  re -dissolve 
after  stirring  for  three  minutes,  is  obtained,  then  add  15  ounces  more  of  dis¬ 
tilled  water.  Set  this  solution  aside  to  settle.  Do  not  filter. 

When  all  is  ready  for  immersing  the  mirror,  add  to  the  silvering  solution  2 
ounces  of  solution  C,  and  stir  gently  and  thoroughly.  Solution  C  may  be  filtered. 

Perfectly  pure  chemicals  may  be  obtained  of  dealers  in  any  of  the  larger 
cities  in  this  country. 

To  prepare  the  Speculum. — Procure  a  circular  block  of  wood  2  in.  thick  and 
2  in.  less  in  diameter  than  the  speculum.  Into  this  should 
be  screwed  three  eye-pins  at  equal  distances,  as  in  Fig.  46. 

To  these  pins  fasten  stout  whipcord,  making  a  secure  loop 
at  the  top. 

Melt  some  soft  pitch  in  any  convenient  vessel,  and  hav¬ 
ing  placed  the  wooden  block  face  upwards  on  a  level  table, 
pour  on  it  the  fluid  pitch,  and  on  the  pitch  place  the  back 
of  the  speculum,  having  previously  moistened  it  with  a  thin 
film  of  spirit  of  turpentine  to  secure  adhesion.  Let  the 
whole  rest  until  the  pitch  is  cold. 

To  clean  the  Speculum. — Place  the  speculum,  cemented  to  the  circular 
block,  face  upwards,  on  a  level  table;  pour  on  it  a  small  quantity 
of  stiong  nitric  acid,  and  rub  it  gently  all  over  the  surface  with  a 
brush  made  by  plugging  a  glass  tube  with  pure  cotton  wool.  (F  ig. 
47.)  Having  perfectly  cleaned  the  surface  and  sides,  wash  well 
with  common  water,  and  finally  with  distilled  water.  Place  the 
speculum  face  downwards  in  a  dish  containing  a  little  rectified  spirit 
of  wine  until  the  silvering  fluid  is  ready. 

To  immerse  the  Speculum. — Take  a  circular  dish  about  3  m- 
deep  and  2  in.  larger  in  diameter  than  the  speculum.  Mix  in  it 

5 


Fit?  47. 


66 


ON  LIGHT. 


the  silvering  solution  and  the  solution  C,  and  suspend  the  speculum,  face 
downwards,  in  the  liquid,  which  may  rise  about  a  quarter  of 
an  inch  up  the  side  of  the  speculum. 

When  the  silvering  is  completed,  remove  the  speculum 
from  the  solution,  and  immediately  wash  with  plenty  of 
water,  using  at  least  two  gallons,  and  finally  with  a  little 
distilled  water.  Place  the  speculum  on  its  edge  on  blotting- 
paper  to  drain  and  dry.  (Fig.  48.) 

When  perfectly  dry,  polish  the  film  by 
gently  rubbing  first  with  a  piece  of  the 
softest  wash-leather,  using  circular  strokes 
(Fig.  49),  and  finally  with  the  addition  of 


1  little  finest  rouge.* 

A  “  flat  ”  may  be  silvered  by  fastening  with  pitch  to  a  slice 
of  cork,  cleaning  as  above  described,  and  using  as  much  sil¬ 
vering  fluid  as  will  form  a  stratum  about  half  an  inch  deep 
beneath  the  mirror. 

To  separate  the  Speculum  from  the  Block. — Stand  the  speculum  on  its  side, 
insert  the  edge  of  a  sharp  half-inch  chisel  between  the  wood  and  glass,  adminis¬ 
tering  two  or  three  gentle  blows,  and  the  block  and  mirror  will  separate  safely 
and  easily.  It  is  preferable  to  obtain  the  aid  of  an  assistant  in  this  operation. 
Any  pitch  which  remains  on  the  back  of  the  mirror  may  be  removed  by 
scraping  and  a  little  turpentine. 

The  cost  of  silvering  an  8-inch  speculum,  exclusive  of  the  cost  of  alcohol, 
which  may  be  used  over  and  over  again,  will  not  exceed  9d., 

N  itrate  of  silver  being  4s.  per  oz. 

Potash  .  .  8d.  „ 

Milk-sugar  .  2d.  .. 

Avoid  all  excess  of  ammonia,  and  be  sure  to  use  pure  distilled  water. 


ON  WORKING  GLASS  SPECULA. 


When  parallel  rays  of  light  are  allowed  to  fall  upon  the  surface  of  a  concave 
mirror,  if  the  surface  be  a  spherical  curve,  the  rays  will  not  all  be  reflected  to 
a  single  point. 

In  F  ig.  50  it  will  be  seen  that  the  rays  A  A,  falling  on  the  mirror,  would  be 


T^e  s’'v?r'nS  W’U  ')e  completed  '*n  from  jo  to  70  minutes,  according  to  temperature;  commutes 
W’li  he  sufficient  in  summer.  * 


THE  REFLECTION  OF  LIGHT 


67 

reflected  and  form  an  image  at  a-,  while  the  rays  B  B  would  be  reflected  and 
form  an  image  at  b,  farther  from  the  front  of  the  mirror. 

If  the  reflected  images  were  viewed  with  an  eye-piece  placed  anywhere  in 
front  of  the  mirror,  they  would  not  be  in  focus  at  the  same  time,  so  that  only 
a  blurred  and  indistinct  image  would  be  seen. 

To  make  the  mirror  reflect  rays  falling  on  all  parts  of  its  surface  to  one 
point,  it  is  necessary  that  it  should  be  fashioned  into  a  parabolic  curve. 


Such  a  curve  is  snovvn  in  Fig.  51,  which  may  be  considered  as  a  spherical 
curve,  in  which  the  curve  has  been  made  deeper  or  the  outer  portion  flattened. 
In  practice  the  amount  of  this  difference  is  so  exceedingly  minute  as  to  be 
inappreciable  by  actual  measurement. 

Sir  John  Herschel  states  that  the  utmost  variation  of  a  4-foot  speculum 
from  a  spherical  curve  is  less  than  than  one  21,000th  part  of  an  inch.  Yet  it 
is  well  known  that  for  telescopic  use  a  mirror  with  a  spherical  curve  is,  for  the 
reason  just  explained,  totally  useless. 

In  working  the  glass  specula,  a  disc  of  hard  crown  glass,  varying  in  substance 
from  three-quarters  of  an  inch  to  one  and  a  half  inches,  according  to  the  size  of 
the  speculum  for  which  it  is  intended,  is  turned,  and  polished  on  the  edge. 
One  side  of  this  disc  is  ground*  to  a  truly  plane  surface.  On  this  side  the 
speculum,  when  mounted  on  the  writer’s  plan,  rests  in  its  cell.  The  other 
side  is  then  ground  to  a  concave  spherical  curve  of  such  a  radius  as  will 
produce  the  desired  focus.  This  spherical  curve  is  converted  into  a  parabolic 
figure  somewhat  thus: 

An  iron  tool,  similar  to  that  on  which  the  spherical  curve  has  been  ground, 
is  covered  with  a  layer  of  pitch,  tempered  to  a  certain  consistency.  This  pitch 
is  warmed,  and  the  speculum  being  laid  upon  it  makes  the  pitch  assun  e  the 
same  curve.  The  speculum  is  then  polished  on  the  pitch  with  rouge.  In  this 
polishing  the  speculum  and  polisher  are  not  worked  together  equally  all  over 
the  surfaces,  but  the  speculum  is  moved  in  such  a  manner  that  it  is  polished 
away  most  towards  the  edge,  and  a  parabolic  curve  is  produced.  During  the 
process  both  the  speculum  and  the  polisher  continually  revolve. 

The  diagram  of  Lord  Rosse’s  machine,  with  which  he  figured  his  speculum 
6  ft.  in  diameter,  will  give  an  idea  of  the  action  of  the  speculum  and  polisher 
on  each  other. 

This  machine  is  represented  in  Fig.  52;  A  is  the  spindle,  by  turning  which 
the  whole  machine  is  set  in  motion  ;  H  I  is  the  speculum ;  K  L,  the  polisher ; 
B,  an  excentric  which  carries  the  polisher  backwards  and  forwards ;  G,  another 
excentric  which  moves  the  polisher  from  side  to  side  slowly  during  the  recipro 

5—2 


' 


Fig.  52. 


ON  LIGHT. 


eating  motion.  The  amount  of  motion  given  to  the  polisher,  and  the  rapidity 
of  rotation  of  the  speculum,  can  be  changed  at  pleasure. 


In  Fig.  53  the  dotted  line  represents  the  spherical  curve  of  the  mirror  when 
the  polishing  is  begun,  and  the  continuous  line  the  parabolic  curve  it  assumes 
when  the  polishing  process  is  finished.  It  will  be,  of  course,  understood  that 
in  all  the  diagrams  these  curves  are  enormously  exaggerated. 


Fig.  53- 

During  the  graduated  polishing  the  speculum  is  repeatedly  tested,  until  the 
desired  definition  is  attained.  When  completed,  if  accurately  figured,  the 
marginal  inch  of  the  speculum  should  give  equally  sharp  definition  with  the 
centre,  and  have  identically  the  same  focus. 


Fig.  54. 

In  figuring  the  mirrors  of  the  telescopes  herein  described,  an  improved 
method  has  been  adopted  of  fashioning  the  parabolic  curve ;  it  is  believed 
this  method  gives  superior  results  to  any  hitherto  attained.* 


*  1  he  reader  who  wishes  for  further  information  on  this  subject  is  referred  to  Sir  John  Herschel’s 
work  on  “The  t  elescope. *’ 


THE  REFRACTION  OF  LIGHT 


69 


THE  REFRACTION  OF  LIGHT. 

When  a  ray  of  light  passes  from  one  medium  to  another  ot  tne  same 
density,  and  in  a  perfectly  straight  line,  no  alteration  of  its  course  takes  place; 
but  if  the  light  passes  in  an  oblique  direction,  its  course  is  broken  ox  refracted, 
i.e.,  bent  back  from  its  natural  path.  To  this  branch  of  optics,  which  includes, 
perhaps,  the  widest  field  of  inquiry,  and  traces  the  propagation  of  light  through 
transparent,  solid,  liquid,  and  gaseous  bodies,  has  been  given  the  name  of 

Dioptrics. 

To  prove  that  a  straight  line  representing  a  ray  of  light  is  really  bent  when 
passing  from  a  rare  medium,  air,  into  a  denser  one,  such  as  water,  nothing  is 
easier  than  to  place  a  bright  shilling  on  the  end  of  an  ivory  paper-knife,  which 
is  inclined  in  a  large  empty  tumbler.  On  looking  down  the  paper-knife  a 
straight  line  only  is  apparent,  terminating  with  the  coin ;  but  if  the  tumbler 
is  filled  with  water  whilst  the  observer  is  still  looking  down  the  flat  surface,  he 


will  notice  that  at  the  point  of  juncture  between  the  air  and  water  a  break 
takes  place,  and  the  end  of  the  paper-knife,  or  all  that  part  immersed,  appears 
to  be  lifted  up  or  bent  upwards  from  its  natural  course  or  direction.  If  a  small 
pocket-pistol  were  now  aimed  at  the  coin  and  the  bullet  discharged  it  would 
certainly  miss,  because  every  visible  object  appears  to  be  in  a  direction  repre¬ 
sented  by  a  straight  line  drawn  from  it  to  the  eye.  A  straight  line  ruled  to 
the  shilling  would  not  touch  it,  the  line  must  be  ruled  to,  or  the  pistol  aimed 
at,  a  point  nearer  to  the  spectator  than  the  apparent  position  of  the  coin. 

The  bending  of  the  ray  is  governed  by  certain  laws  known  as  “  Descartes’ 
Laws.” 

Firstly.  Whatever  the  obliquity  of  the  incident  ray,  the  sine  of  the  incident 
angle  and  the  sine  of  the  angle  of  refraction  are  in  a  constant  ratio  for  the 
same  two  media,  but  vary  with  different  media. 

Secondly,  The  incident  and  the  refracted  rays  are  in  the  same  plane,  which 
is  perpendicular  to  the  surface  separating  the  two  media. 

A  \ery  complete  French  apparatus  (Fig.  56),  described  in  Ganot’s  “  Physics.” 


70 


ON  LIGHT. 


is  made  for  the  purpose  of  proving  those  laws  experimentally.  It  consists  of 
a  large  and  carefully  graduated  circle  supported  on  a  tripod  stand.  In  the 
centre  is  placed  a  semi-cylindrical  glass  vessel  filled  with  water,  or  any  other 
fluid  whose  index  of  refraction  it  is  required  to  ascertain,  so  that  the  level  of 
the  fluid  coincides  with  the  height  of  the  centre  of  the  circle.  From  the 
mirror  A,  a  ray  of  light  is  reflected  through  a  hole  in  the  screen  B,  and  falls 
on  the  surface  of  the  water  at  C.  Passing  through  the  water,  the  course  of  the 

refracted  ray  is  traced  to  a  screen  D,  on  which 
the  circular  image  is  received.  In  the  various 
positions  of  the  screens  B  and  D,  attached  to 
arms  radiating  from  the  centre  C,  the  sines  of 
t  le  angles  of  incidence  and  refraction  are  ob¬ 
tained  and  measured  by  two  graduated  rules 
E  F,  movable  so  as  to  be  always  horizontal, 
and  therefore  perpendicular  to  the  diameter 
G  H. 

The  numbers  vary  with  the  positions  of  the 
screens,  but  the  sines  of  the  incident  and  re¬ 
fracted  rays  are  in  a  constant  ratio  to  the  same 
two  media,  viz.,  air  and  water.  If  the  sine  of 
the  incident  ray  is  doubled,  the  sine  of  the 
refracted  one  will  increase  in  the  same  ratio. 

When  another  fluid  is  put  into  the  trough, 
a  variation  in  the  sines  would  occur,  and  it  is 
in  this  manner  the  first  law  is  proved.  By 
moving  the  mirror  and  screen  B,  so  that  the 
light  falls  perpendicularly  on  the  surface  of 
the  water,  the  instrument  proves  the  second 
law,  as  there  cannot  then  be  any  angle  formed, 


or  sines  to  record  or  measure. 

Supposing  the  sine  of  the  angle  of  refraction  in  the  above  experiment  with 
air  and  water  to  measure  12  in.,  and  the  sine  of  the  angle  of  incidence  16  in., 
it  would  follow  that  in  water  the  sine  of  the  angle  of  incidence  is  to  the  sine 
of  the  angle  of  refraction  as  i  '336  to  1,  or  as  nearly  as  possible  ij  to  1.  The 
number  1  "336,  which  expresses  this  ratio  for  water,  is  called  the  index  of  in¬ 
fraction  for  water,  and  sometimes  its  refractive  power. 

The  determination  of  the  refractive  powers  of  various  kinds  of  glass  is  of 
great  use  in  the  manufacture  of  achromatic  telescopes;  and  sometimes  the 
purity  of  a  liquid,  and  its  freedom  from  adulteration,  may  be  approximately 
ascertained  by  taking  the  index  of  refraction. 

In  the  chapter  devoted  to  the  consideration  cf 
the  reflection  of  light,  it  was  thought  to  be  the  most 
simple  and  instructive  plan  to  trace  the  progress 
of  parallel  rays  when  thrown  off  from  plane,  con¬ 
cave,  or  convex  surfaces. 

The  forms  of  refracting  bodies,  and  their  action 
on  light,  are  so  numerous  and  well  discussed  in 
the  more  elaborate  works  on  Dioptrics,  that  it  is 
mere  repetition  to  quote  them  all. 

The  laws  of  refraction  being  known,  and  the  1  c 

refractive  power  of  the  glass  used  for  experiment  Fig.  57. 


THE  REFRACTION  OF  LIGHT. 


7i 


being  ascertained,  the  mathematician  may  work  out  on  paper  the  exact  direc¬ 
tion  of  the  light  passing  into  or  out  of  the  most  complicated  forms.  As  an 
illustration  of  this  mode  of  investigation,  the  following  instructions  are  given 
by  Brewster,  in  order  to  enable  the  student  to  study  the  refraction  of  light 
through  one  of  the  most  important  optical  instruments,  viz.,  the  Prism.  (Fig. 
57-) 

An  optical  prism,  a  solid  having  three  plane  surfaces.  A  B,  A  c,  called  its 
refracting  surfaces ;  B  c  is  called  the  base  of  the  prism. 

Let  ABC  (Fig.  58)  be  a  prism  of  plate  glass,  whose  index  of  refraction  is 
1*500,  and  let  H  R  be  a  ray  of  light  falling  obliquely  upon  its  first  surface  A  B 
at  the  point  R.  Round  R,  as  a  centre,  and  with  any  radius  H  R,  describe  the 
circle  H  M  b.  Through  R  draw  M  R  N  perpendicular  to  A  B,  and  H  in  perpen¬ 
dicular  to  M  R.  The  angle  H  R  M  will  be  the  angle  of  incidence  of  the  ray 
H  R,  and  H  in  its  sine,  which  in  the  present  case  is  r5co.  Then,  having 
made  a  scale  in  which  the  distance  H  m  is 
1*500,  or  1 5  parts,  take  one  part  or  unity 
from  the  same  scale,  and  having  set  one 
foot  of  the  compasses  on  the  circle,  some¬ 
where  about  b,  move  it  to  different  points 
of  the  circle  till  the  other  foot  strikes  only 
one  point  11  of  the  line  R  N  ;  the  point  b 
thus  found  will  be  that  through  which  the 
refracted  ray  passes,  R  b  will  be  the  re¬ 
fracted  ray,  and  n  R  b  the  angle  of  refrac¬ 
tion,  because  the  sine  b  n  of  this  angle 
has  been  made  such,  that  its  ratio  to  H  in, 
the  sine  of  the  angle  of  incidence,  is  as 
I  to  1*500.  The  ray  R  b  thus  refracted 
will  go  on  in  a  straight  line  till  it  meets 
the  second  surface  of  the  prism  at  R  r',  when  it  will  again  suffer  refraction  in 
the  direction  R  b'.  In  order  to  determine  this  direction,  make  R'  h' equal 
to  R  H,  and,  with  this  distance  as  radius,  describe  the  circle  H '  b'.  Draw 
R'  N  perpendicular  to  A  C,  and  H'  in  perpendicular  to  R  N,  and  form  a  scale  on 
which  H- ;//' shall  be  one  part,  or  rooo,  and  divide  it  into  tenths  and  hun¬ 
dredths.  From  this  scale  take  in  the  compasses  the  index  of  refraction  1*500 
as  is  of  these  parts  ;  and,  having  set  one  foot  somewhere  in  the  line  R'  ti, 
move  it  to  different  parts  of  it  till  the  other  foot  falls  upon  some  part  of  the 
circle  about  b-,  taking  care  that  the  point  b'  is  such,  that  when  one  foot  of  the 
compasses  is  placed  there,  the  other  foot  will  touch  the  line  R'  b' ,  continued 
only  in  one  place,  join  R'  b ,  Then,  since  H'  R'  nv  is  the  angle  of  incidence,  or 
the  second  surface  A  C  and  H' m  its  sine,  and  since  n  b' ,  the  sine  of  the  angle 
b  R  it',  has  been  made  to  have  to  h'  in’  the  ratio  of  1*500  to  1,  b‘  R'  11  will  be 
the  angle  of  refraction,  and  R'  b'  the  refracted  ray.  In  the  construction  of  the 
figure  (Fig.  58)  the  ray  H  R  has  been  made  to  fall  upon  the  prism  at  such  an 
angle  that  the  refracted  ray  R  r'  is  equally  inclined  to  the  faces  A  B,  A  C  ;  or 
is  parallel  to  the  base  B  C  of  the  prism  ;  and  it  will  be  found  that  the  angle  of 
incidence  H  R  B  is  equal  to  the  angle  of  emergence  b'  r'  C.  Under  these  cir¬ 
cumstances,  we  shall  find,  by  working  the  angle  H  R  B  either  greater  or  less 
than  «t  is  in  the  figures,  that  the  angle  of  deviation  H  E  D  is  less  than  at  any 
other  angle  of  incidence.  If  we,  therefore,  place  the  eye  behind  the  prism  at 
b,  and  turn  the  prism  round  in  the  plane  R  A  C,  sometimes  bringing  A  towards 


ON  LIGHT. 


the  eye  and  sometimes  pushing  it  from  it,  we  shall  easily  discover  the  position 
when  the  image  of  the  candle  seen  in  the  direction  b'  D  has  the  least  devia¬ 
tion.  When  this  position  is  found,  the  angles  H  R  B  and  b  r'  C  are  equal, 
and  R  R'  is  parallel  to  B  C,  and  perpendicular  to  A  F,  a  line  bisecting  the 
refracting  angle  B  A  C  of  the  prism  ;  but  since  B  A  F  is  known,  the  angle  of 
refraction  B  R  N  is  also  known ;  and  the  angle  of  incidence  H  R  B  being  found 
by  the  preceding  methods,  we  may  determine  the  index  of  refraction  for  any 
prism  by  the  following  analogy  : — 

As  the  sine  of  the  angle  of  refraction  is  to  the  sine  of  the  angle  of  incidence, 
so  is  unity  to  the  index  of  refraction  ;  or  the  index  of  refraction  is  equal  to 

the  sine  of  the  angle  of  incidence  divided  by  the 
sine  of  the  angle  of  refraction.  By  this  method 
we  may  readily  measure  the  refractive  power  of 
all  bodies.  If  the  body  be  solid,  it  must  be  shaped 
into  a  prism  ;  and  if  it  is  soft  or  fluid,  it  must  be 
placed  in  the  angle  B  A  C  of  a  hollow  prism,  ABC, 
(Fig.  59)  made  by  cementing  together  three  pieces 
of  plate  glass,  A  B,  A  C,  B  C.  A  very  simple  hollow 
prism  for  this  purpose  maybe  made  by  fastening 
together  at  any  angle  two  pieces  of  plate  glass,  A  B,  A  C,  with  a  bit  of  wax  F. 


A  drop  of  the  fluid  may  then  be  placed  in  the  angle  at  A, 
retained  by  the  force  of  capillary  attraction. 

TABLE  OF  THE  INDICES  OF  REFRACTION. 

when 

it  will  be 

Vacuum  . 

I  ‘OOOOOO 

Lens,  Crystalline 

1-384 

Air  .... 

1  ‘000294 

„  Vitrous  . 

1-339 

Albumen  . 

1-360 

„  Aqueous  . 

I-336 

Alcohol 

1 ‘374 

Nitrous  Oxide  Gas 

1  ‘000503 

Ammonia  Gas. 

1 ‘000385 

Nitric  Acid 

1 ‘410 

Alum 

1 ‘457 

Oxygen 

1  '000272 

Amber 

i*547 

Olefiant  Gas 

rooo678 

Bisulphide  of  Carbon 

1*678  * 

Oil,  Olive  . 

i-47o 

Carbonic  Acid  Gas  . 

1  ‘000449 

„  Turpentine. 

i'475 

Chlorine  Gas  . 

1 ‘000772 

„  Castor 

1-490 

Diamond  . 

2‘439 

„  Cloves 

1-535 

Ether 

I-358 

„  Cassia 

r64i 

Fluid  Spar 

1-434 

Phosphorus 

2-424 

Glass,  Flint 

1 ‘605 

Quartz 

1-548 

„  Plate 

1-543 

Ruby 

1-779 

„  Crown  . 

1-534 

Sapphire  . 

1-794 

Garnet 

1  "8 1 5 

Sulphur 

2‘I  I  5 

Hydrogen . 

1 ‘000138 

Sulphuric  Acid  Gas 

I ‘000665 

Hydrochloric  Acid  Gas 

1  ‘000449 

Sulphuric  Acid. 

1-434 

Hydrochloric  Acid  . 

i‘4io 

Tabasheer 

I’ll! 

Iceland  Spar — 

Water 

1-336 

Ordinary  ray . 

1-654 

„  Solid  (Ice) 
Zircon 

f3IO 

Extraordinary  ray . 

1-483 

I  '961 

1  he  course  of  parallel  rays  of  light  through  plane,  concave,  and  convex 


*  Used  to  fill  prisms  for  spectrum  analysis. 


THE  REFRACTION  OF  LIGHT. 


73 


surfaces  of  glass  may  now  be  considered,  and  they  will  be  found  to  contrast 
in  the  most  simple  manner  with  similar-shaped  reflecting  surfaces. 


t 


Fig.  6o. 


Refraction  of  Light  through  Plane  Glass. 

Let  A  B  (Fig.  60)  be  a  ray  of  light  incident  on  the  upper  surface  or  side  of  a 
piece  of  ordinary  plate  glass,  marked  C  C,  whose  other  or  under  side,  D  D,  is 
parallel  to  C  C.  On  entering  the  glass  the  ray  is  refracted  in  the  direction 
B  E,  and  it  will  be  refracted  again  at  its  exit  from  the  under  side,  D  D,  to  the 
same  amount  as  at  its  entrance  in  the  line  E  F ;  consequently  an  eye  placed  at 
F  would  see  the  ray  as  if  it  came  from  the  point  a’  along  the  line  F  E  a'.  The 
light  has  undergone  refraction,  and  an  object  seen  through  a  window  is  not 
seen  in  its  true  position ;  but,  as  parallel  rays  falling  upon  a  plane  glass  retain 
their  parallel  lines  after  passing  through  it,  the  object  does  not  appear  to 
undergo  any  change  unless  the  two  surfaces  of  the  glass  are  uneven,  and  not 
parallel  with  each  other,  when  distortion  takes  place.  Such  an  effect  is 
rarely  seen  now  in  looking  through  the  windows  of  good  houses,  because  they 
are  usually  glazed  with  plate  glass,  the  sides  of  which  are  nearly  parallel.  It 
has  already  been  shown  that  convex  mirrors  (page  22)  render  parallel  rays  of 
light  divergent ;  precisely  the  reverse  occurs  with  convex  refracting  surfaces. 

Refraction  of  Parallel  Rays  of  Light  by  Convex  Surfaces. 

Fig.  61  represents  a  piece  of  glass  cut  into  the  form  of  a  double-convex  lens 
A  B,  a  figure  such  as  would  be  pro¬ 
duced  by  placing  one  watch-glass  on 
the  edge  of  another  having  precisely 
the  same  amount  of  convexity.  Let 
C  D  be  a  ray  of  light  falling  perpen¬ 
dicularly  on  the  refracting  surface 
and  passing  straight  through  the 
glass,  in  obedience  to  the  law  al¬ 
ready  enunciated,  that  a  ray  of  light 
which  falls  perpendicularly  on  a  re¬ 
fracting  surface  undergoes  no  change 
in  its  direction,  and  therefore  C  D 
passes  through  the  middle  or  axis 


B 


Fig.  61. 


74 


ON  LIGHT. 


of  the  crystal  lens  without  deviation  from  a  straight  line  C  D  E.  The  other 
two  rays,  F  G,  H  I,  falling  at  an  angle  on  the  glass,  undergo  refraction,  and  are 
bent  towards  and  emerge  from  the  other  side,  and  meet  at  the  point  E,  called 
the  principal  focus,  or  focus  for  parallel  rays.  These  parallel  rays  of  light  are 
refracted  by  a  double-convex  lens,  and  become  convergent,  meeting  at  a  point 
called  the  focus.  On  the  other  hand,  if  E  be  considered  as  the  luminous  point 
from  which  divergent  rays  are  emitted,  they  become  parallel  rays  when  they 
emerge  from  the  double-convex  lens  A  B. 


Refraction  of  Parallel  Rays  by  Concave  Surfaces. 

Let  A  B  (Fig.  62)  be  a  glass  lens,  whose  two  sides  are  hollowed  out,  or 
concave,  and  C  D  a  ray  of  light  falling  perpendicularly  on  the  surface,  and 

therefore  passing  straight  through 
the  lens.  F  G  and  H  I  are  two  other 
rays  impinging  on  the  surface  of  the 
glass  at  an  angle ;  these  undergo  re¬ 
fraction,  and  are  bent  outwards  in 
the  direction  F  G  K  and  H  I  K. 

Thus  the  property  of  a  concave 
lens  is  just  the  reverse  of  a  concave 
mirror,  the  former  causing  parallel 
rays  of  light  to  become  divergent, 
P  ,  .  the  latter  convergent;  and  if  the  rays 

'  K  K  be  regarded  as  convergent  rays, 

.  they  become  parallel  when  emerg¬ 

ing  from  the  concave  lens  A  B. 


Other  Forms  of  Lenses. 

F01  various  optical  purposes  a  variety  of  lenses,  in  addition  to  the  prism, 
the  double  convex,  or  the  double  concave  lenses,  is  required,  which  may  be 
ground  into  the  following  forms: 


a.  A  spherical  lens,  causing  parallel  rays  to  become 
convergent  . 


A  AgjjSn°  c<mvex  lehS;  Pamllel  *3*  become  Convex 

. 


Fig.  63. 


THE  REFRACTION  OF  LIGHT. 


75 


c.  A  plano-concave  lens  ;  parallel  rays  become  diver¬ 
gent  o  •  •  •  •  ®  •  •»  • 


d.  A  meniscus ;  parallel  rays  become  convergent  . 


e.  A  concavo-convex  lens ;  when  the  concavity  exceeds 
the  convexity,  parallel  rays  become  divergent 


It  is  good  practice  for  the  student  in  physics  to  make  careful  drawings  of 
the  above  figures,  and  to  trace  the  paths  of  imaginary  rays  of  light  through 
them.  The  drawings  may  be  varied  by  supposing  the  lenses  to  be  made  of  any 
of  the  solid  transparent  substances  whose  refracting  indices  are  given  in  the 
table  at  page  52. 

- ♦ - 

OPTICAL  INSTRUMENTS  WHOSE  PROPERTIES  DEPEND 

ON  REFRACTION. 

The  Simple  and  Compound  Microscope  and  Telescope. 

It  follows  from  the  laws  of  refraction  already  explained,  that  when  a  double- 
convex  lens  (P  ig.  64)  acts  on  rays  proceeding  from  an  object,  such  as  a  candle, 
A  B,  that,  as  the  rays  are  not  all  parallel,  they  will  be  collected  into  a  focus 
t.'B'at  a  distance  behind  the  lens  somewhat  greater  than  the  focus  for  parallel 
rays  at  E,  and  that  an  inverted  image  of  the  candle  A  B  will  be  produced  at 
A"  B,  which  may  be  received  on  any  white  surface.  Thus  a  double-convex 
lens  becomes  the  most  simple  microscope  which  can  be  used,  and  it  is  some¬ 
times  used  for  that  purpose  in  the  examination  of  samples  of  wheat.  The 


Fig.  63. 


76 


ON  LIGHT. 


cheapest  thoroughly  good  and  really  useful  microscope  the  author  has 
seen  costs  half  a  dollar.  It  includes  a  lens  made,  seemingly,  of  a  fila¬ 
ment  of  glass  melted  into  a  globule,  fitted  into  a  brass  tube  which  con¬ 
tains  a  plate  of  glass  to  be  used  as  an  object-holder  (such  as  for  the  eels 

in  paste),  and  the  opposite  end  of  the  brass 
tube  is  closed  with  a  diaphragm,  which  can  be 
unscrewed  if  more  light  is  required.  The  whole 
is  fitted  into  a  case,  and  might  be  made  a  very 
amusing  companion  for  young  people  when  they 
go  into  the  fields  ;  and  if  lost,  the  value  is  not  an 
alarming  consideration.  For  the  use  of  botanists 
and  other  observers,  much  cheaper,  yet  very 
effective,  lenses  are  made.  Another  marvel  of 
cheapness  is  a  telescope  of  great  excellence 
which  is  sold  for  three  dollars.  The  latter,  of 
course,  is  not  achromatic ;  but  its  definition  of 
distant  objects  is  really  excellent,  and  the  work¬ 
manship  good. 

In  the  compound  microscope  the  image  a'  b/ 
(Fig.  64)  is  still  further  magnified,  and  can  be 
more  carefully  examined  by  the  addition  of  an¬ 
other  double-convex  lens,  say  of  an  inch  focal 
distance.  It  is  the  image  formed  in  the  tube  of 
the  compound  telescope,  which  may  be  again 
magnified  by  employing  a  second  lens  with  a 
very  short  focus.  In  these  cases  the  first  lens  is 
called  the  object-glass,  and  the  second  the  eye¬ 
piece  or  glass.  Of  late  years  the  most  elaborate 
and  perfect  microscopes  have  been  made  in  this  country  ;  so  that  America 
stands  unsurpassed  in  this  branch  of  optical  instruments,  whilst  her  micro¬ 
scopical  societies  have  contributed  largely  to  our  scientific  knowledge. 


Fig.  65. — Simple  Microscope, 

in  which  the  Lens  is  focused 
turning  the  Screw. 


Fig.  66. —  The  Compound  1  elescope. 


THE  REFRACTION  OF  LIGHT. 


77 


B,  The  object-glass,  which  throws  an  inverted  image  into  the  dark  tube ;  C  is 
the  eye-glass,  which  magnifies  the  inverted  image.  This  telescope  could  only 
be  used  for  astronomical  purposes ;  but,  by  the  addition  of  two  other  convex 
lenses  at  D  E,  called  erecting-glasses,  an  erect  image  is  obtained. 

The  Camera  Obscura. 

A  dark  chamber  into  which  a  double-convex  lens  is  fitted.  The  invention 
of  this  pleasing  contrivance  has  been  usually  ascribed  to  Baptista  Porta,  as  it 
appears  in  his  “  Magica  Naturalis,”  lib.  xvii.,  cap.  vi.,  first  published  at  Frank¬ 
fort  about  1589  or  1591. 

Fifty  years  ago  the  camera  obscura  was  more  popular  than  it  is  now,  and 
was  frequently  erected  on  elevated  spots  of  ground  by  wealthy  individuals, 
the  consequence  being  that  the  whole  apparatus  and  the  building  to  which  it 
was  attached  were  most  carefully  made  and  adjusted  to  each  other. 


Fig.  6 7. 


Fig.  67  represents  a  dome  or  cupola  placed  over  a  room  erected  for  the 
purpose  of  a  camera  obscura.  The  whole  dome,  which  carries  the  box  and 
containing  a  mirror  placed  at  an  angle  over  a  double-convex  lens,  may  be 
made  to  turn  round  on  friction-wheels;  or,  what  is  more  simple,  the  box  is 
made  movable  in  a  groove  upon  the  dome,  and  may  be  turned  with  a  long 
rod  by  a  person  inside.  The  box  is  recommended  to  be  of  a  cubical 
form,  of  about  6  or  7  in.  square,  and  contains  a  carefully  ground  plain  silvered 
mirror,  which  should  be  made  of  parallel  glass  placed  diagonally  in  the  box; 
the  mirror  itself  should  be  attached  by  hinges  at  the  lower  end,  so  that  a 
different  angle  may  be  obtained  if  required.  Underneath  the  mirror,  in  a 
round  cell  at  the  bottom  of  the  box,  is  fixed  a  double-convex  lens,  about  6  or 
8  ft.  focus  and  4  or  5  in.  in  diameter;  this  lens  will  form,  upon  a  white  table 


78 


ON  LIGHT. 


placed  on  the  floor  below,  the  image  of  the  objects  reflected  by  the  mirror 
above  at  the  focal  distance  of  the  lens.  The  diameter  of  the  table  should  be 

2\  or  3  ft.,  and,  in  order  to  cor¬ 
rect  the  indistinct  images  formed 
at  the  edge  by  spherical  aberra¬ 
tion,  it  is  usual  to  make  the  sur¬ 
face  slightly  concave,  and  to  form 
it  of  the  best  plaster  of  paris  or 
stucco.  The  table  should  be  sup¬ 
ported  by  a  pillar  in  the  centre, 
fitting  into  a  tube  provided  with 
a  screw,  so  that  the  table  may  be 
raised  or  lowered,  and  the  images 
exactly  focused  on  its  surface.  A 
still  more  perfect  optical  arrange¬ 
ment  for  projecting  brilliant 
images  of  distant  objects  on  to  a 
white  surface  for  the  purposes  of 
the  artist  is  shown  in  the  figure 
annexed.  (Fig.  68.) 

In  this  camera  the  rays  of  light, 
after  falling  on  the  convex  sur¬ 
face,  enter  the  prism,  and,  being 
totally  reflected  from  the  side  A  B, 
pass  into  the  box  through  the 
concave  surface,  and  fall  upon  a 
sheet  of  paper  laid  out  on  a  pro¬ 
per  framework.  The  picture  thus 
obtained  has  not  the  fault  of 
those  produced  by  the  ordinary 
arrangement  of  the  mirror  or  con¬ 
vex  lens,  being  free  from  spherical 
aberration,  which  is  neutralized 
in  this  instance  by  the  concave 
surface  of  the  prism.  As  these 
prisms  are  difficult  to  make,  the 
same  result  is  attained  by  care¬ 
fully  cementing  with  Canada  bal¬ 
sa  m  a 
plano¬ 
convex 
lens  on 

c  .  one  side 

ot  the  prism,  and  a  plano-concave  on  the  other,  whose 
focal  lengths  are  equal  to  each  other.  (Fig.  69.) 

The  magic  lantern  apparatus,  the  dissolving  view 
and  the  phantasmagoria  lantern  apparatus,  are  all 
retracting  optical  instruments,  very  easily  constructed. 

Ihe  magic  lantern  was  contrived,  about  the  year  Fir  60 

hi^wnV  1C  K'ICher’  anc*  ,is  described  in  a  b  c,  the  prism,  with  piano- 

his  woi k  entitled,  Ars  Magna  Lucis  et  Umbra?”  convex  and  plano-concave 

lens  attached  at  A  E  and  CS. 


F ig.  68. —  The  Prism  Camera. 

D  D  d,  section  of  a  pyramidal  box ;  m,  a  brass  tube  open 
on  one  side,  moving  in  another  tube,  and  containing 
the  rectangular  prism  a  b  c,  one  side  of  which,  a  c,  is 
convex,  and  the  other,  c  b,  concave;  o,  the  framework 
to  support  the  sheet  of  paper. 


THE  REFRACTION-  OF  LIGHT 


79 


There  is,  however,  a  curious  account  of  phantom  figures  or  demons,  made  to 
appear  in  the  smoke  of  a  fire  and  thrown  upon  walls,  ascribed  to  Cellini,  who 
lived  nearly  a  century  before  Kircher.  If  the  story  be  true,  it  would  seem  to 
show  that  phantasmagorial  effects  preceded  the  magic-lantern  pictures,  and 
that  Cellini  must  have  been  acquainted  with  the  construction  of  the  instrument, 
or  such  effects  as  described  could  not  have  been  produced.  The  magic  lantern 
consists  of  a  box  provided  with  a  chimney,  containing  a  good  lamp,  or,  still 
better,  an  oxy-hydrogen  light  ;  when  the  former  is  used,  a  reflector  is  usually 


F IG.  70. — Common  Magic  Lantern. 

B.  the  box  ;  c,  the  lamp  aiul  reflector ;  a,  the  plano-convex  lens ;  c  c,  the  tube  sliding  within  the.  first 
tube,  and  containing  a  double-convex  lens,  a'. 


placed  behind  the  flame,  in  order  to  increase  the  illumination  of  the  pictures. 
The  lime-light  is  placed  behind  the  lenses  called  condensers  (Fig.  71);  these  are 
usually  composed  of  two  plano-convex  lenses,  with  the  flat  side  placed  towards 
the  lamp,  and  the  convex  side  touching,  or  nearly  so,  the  convexity  of  the  other 
lens,  the  flat  side  of  which  is  towards  the  picture.  The  picture,  painted  or 
carefully  photographed  on  glass,  is  placed  in  front  of  the  condensers,  and  the 


whole  projected  and  properly  fo¬ 
cused  on  a  white  screen  by  means 
of  two  other  plano-convex  lenses  ; 
the  flat  side  of  one  lens  being  to¬ 
wards  the  picture,  and  the  convex 
side  towards  the  flat  side  of  the 
second  lens.  The  focusing  lenses 
are  contained  in  a  tube  which  slides 
within  the  other,  and  is  moved  back¬ 
wards  and  forwards  with  a  simple 
rack-work. 

The  dissolving  view  arrangement, 
long  kept  a  secret  by  Mr.  Child,  the 
inventor,  is  nothing  more  than  two 
magic  lanterns  (Figs.  74,  75)  placed 
side  by  side,  and  provided  with  slid¬ 
ing  plates  so  arranged  that,  as  one 
picture  is  gradually  cut  off,  the  second 


Fig.  71. — Section  of  Superior  Magic 
Lantern. 

.,  oxv-hydroger  light;  B.  the  condenser;  c,  the  place 
to  contain  pictures;  D,  the  focusing  lenses;  E  E,  the 
diaphragm  to  reduce  the  aberration  of  light. 


8o 


ON  LIGHT. 


is  disclosed;  and  byalternately  throwing  on  one  picture  and  cutting  off  theother, 
the  most  pleasing  effects  are  obtained,  provided  the  two  lanterns  are  precisely 
similar.  To  save  gas,  it  is  sometimes  usual  to  turn  off  the  oxygen  from  one 
lantern  and  to  supply  it  to  the  other,  and  thus  by  alternately  raising  and 
lowering  the  lights  in  the  lanterns  the  same  result  is  obtained.  (Fig.  76.) 

The  phantasmagorial  effects  first  ascribed  to  Cellini  are  produced  by  painting 
in  the  figure-picture  on  glass,  and  then  blackening  out  the  whole  of  the 

ground,  and  —  either  by  carrying  the 
lantern  and  moving  backwards  and 
forwards  behind  the  sheet,  or  by  a  me¬ 
chanical  arrangement  in  which  the  lan¬ 


tern  runs  on  a  tramway,  and  is  focused 
as  it  approaches  or  recedes  from  the 
transparent  disc — the  pictures  are  made 
to  increase  or  diminish  at  pleasure.  In 
practice  it  is  better  to  allow  the  lantern 
and  person  showing  it  to  be  carried  on 
the  same  carriage,  as  the  lever  arrange¬ 
ment — shown  in  Fig.  72,  and  attached 
to  the  focusing  lenses — is  very  apt  to 
get  out  of  order. 

One  of  the  most  useful  instruments 
for  public  exhibitions  is  the  lantern 
represented  by  Fig.  73,  page  81. 
It  serves  the  purpose  of  producing 
enlarged  images  upon  a  screen  (similar 
to  those  of  the  magic  lantern)  from 
opaque  objects ,  such  as  photographs, 
carte  de  visites,  engravings,  drawings, 
relievos,  natural  objects  in  all  their 
colours,  mechanical  apparatus,  or  deli¬ 
cate  mechanism  in  motion,  such  as  the 
various  parts  of  a  watch  or,  still  better, 
of  a  repeating  watch.  The  instrument 
is  simple  in  its  construction,  and  con¬ 
sists  of  a  lantern  box,  containing  in  the 
centre  a  pillar  with  adjusting  screw, 
upon  which  the  lime  cylinder  is  placed  ; 
behind  it  the  metallic  reflector,  which 
must  be  so  adjusted  that  the  picture  is 
evenly  illuminated.  The  reflector  can  be  raised  or  lowered,  or  moved  back¬ 
wards  and  forwards  ;  it  receives  the  light,  and  throws  it  upon  the  condensing 
lens,  by  which  it  is  concentrated  upon  the  picture  placed  in  the  sliding  door 
in  the  angular  box  joined  to  the  square  compartment.  The  light  thrown  off 
from  the  highly  illuminated  picture  is  received  by  the  achromatic  objective 
lenses  (the  focus  of  which  is  adjusted  by  the  rack  upon  them),  and  projected 
upon  the  screen.  I  he  angular  compartment  may  be  removed,  and  replaced 
by  a  part  with  lenses  for  direct  light  and  transparent  pictures,  as  in  the  ordi¬ 
nary  magic  lantern. 

An  oyster  directly  after  it  is  opened,  the  half  of  an  orange,  particularly 
if  squeezed,  as  the  effect  is  most  ridiculous,  the  juice  and  pips  appear  to  fall 


THE  REFRACTION  OF  LIGHT 


8 1 


upwards — all  bodies  being  reversed  in  this  instrument,  the  hand  and  orange 
are  shown  upside  down — the  human  hand,  the  face  of  a  watch,  a  gold  or 


Fig.  73. — Part  Section  and  Elevation  of  Chadburn’s  Lantern. 

A,  the  light ;  b,  rellectoc,  c,  condensing  lens ;  u,  the  picture  ;  e,  the  achromatic  focusing  lenses. 


Fig.  74. — Improved  Dissolving  View  Apparatus  by  Hig/iley* 

silver  coin,  and  photographs  of  noted  persons,  are  all  good  objects  for  this  in¬ 
strument.  In  1857  the  writer  introduced  at  the  Polytechnic  photographs  of 

*  N.  B. — As  Messrs.  Highley  no  longer  make  dissolving  view  apparatus,  the  reader  is  referred  to 
any  respectable  dealer  in  optical  or  philosophical  instruments. 


S2 


ON  LIGHT. 


I' IG>  76.  Arrangement  for  saving  oxygen  gas,  which  is  supplied  alternately 
to  one  lime  light  and  then  to  the  other. 

way,  and  were  most  effective  and  successful,  as  every  touch  of  the  original 
artist  is  thus  delineated  in  the  photograph  and  subsequently  thrown  on  the 


drawings  made  by  Mr.  George  Hine,  the  distinguished  artist.  The  whole  of 
the  pictures  illustrating  the  amusing  story  of  Blue  Beard  were  done  in  this 


Fig.  75. 


— Section  of  High  ley’s  Dissolving  View  Apparatus  (Fig.  74). 


THE  REFRACTION  OF  LIGHT. 


83 


Fig.  77. — High/e/s  complete  Apparatus  for  Dissolving  Views,  all  packed  in 

two  /foxes. 

screen.  Messrs.  Negretti  and  Zambra  followed  up  the  idea  by  using  photo¬ 
graphs  of  statuary,  which  they  displayed  at  Manchester  with  astonishing 
success,  the  Mechanics’  Institution  there  realizing  something  like  ^600  by  the 
exhibition  in  a  few  months.  Mr.  Highley  has  continued  in  the  same  track, 
and  deserves  notice  for  the  admirable  photographs  of  natural  objects  which 
he  prepared  for  the  dissolving-view  apparatus — his  arrangement  of  the  latter 
contrivance,  shown  in  Fig.  74  and  in  section  Fig.  75’  ’s  &°°d  and  convenient. 
The  arrangement  for  saving  oxygen  gas  (Fig.  76)  is  also  extremely  useful  where 
the  gas  cannot  be  obtained  easily.  Portability  and  economy  of  space  have 
all  been  carefully  studied  by  Highley  in  Fig.  77.  where  the  gases  (oxygen  or 
hydrogen)  are  condensed  in  separate  strong  copper  cylinders  which  pack  in 
one  box,  and  the  lantern,  the  slides,  and  the  stand  upon  which  they  are  placeo. 
come  out  of  and  belong  to  the  second  box. 

f. 


84 


ON  LIGHT. 


THE  HUMAN  EYE. 

This  elaborate  and  wonderful  work  of  the  Creator,  built  up  of  the  usual 
constituents  of  animal  substances,  viz.,  albumen,  gelatine,  fibrine,  with  a  little 
fatty  matter,  all  marvellously  shaped  and  fitted  to  their  purposes,  repre¬ 
sents  an  optical  instrument  which  transcends  every  contrivance  made  by 
the  hand  of  man.  The  camera  obscura  is  the  nearest  approach  to  an  imita¬ 
tion  of  the  eye.  It  is  fitted  with  a  double-convex  lens  ;  the  rays  of  light 
thrown  off  from  any  object  placed  before  the  apparatus  are  brought  to  a  focus, 
and  received  upon  a  sheet  of  paper  or  piece  of  ground  glass.  In  the  eye  the 
same  result  is  brought  about  by  the  refraction  of  light  in  the  crystalline  lens 
and  the  other  humours  ;  the  rays  are  brought  to  a  focus,  and  impinge  upon 
a  nerve,  spread  out  as  a  delicate  network  to  catch  the  beams,  and  to  vibrate  in 
sympathy  with  those  exquisite  undulations  which  cause  the  propagation  of 
light,  and  thus  to  produce  the  sensation  of  vision.  Anatomists  have  given 
this  organ  their  most  careful  attention,  and  published  elaborate  drawings  of 
the  various  parts  of  the  eye.  By  the  permission  of  Messrs.  Chadburn,  of  Shef¬ 
field,  a  copy  of  their  instructive  diagrams  of  the  eye  is  added  (page  65). 

A.  The  Pupil,  or  circular  opening  in  the  iris,  capable  of  being  contracted 
or  enlarged,  according  to  the  amount  and  intensity  of  light. 

B.  The  Iris,  a  flat  circular  membrane,  of  a  grey,  blue,  or  black  colour, 
forming  the  anterior  and  posterior  chambers  of  the  eye.  It  performs  the 
same  functions  as  a  diaphragm  in  an  optical  instrument. 

C.  The  Sclerotic  Coat,  a  tough  white  membrane,  to  which  the  muscles 
for  moving  the  eyeball  are  attached. 

D.  The  Eyelids,  containing  the  tarsal  fibro-cartilages. 

E.  The  Cornea,  composed  of  tough  transparent  laminae,  forming  the  front 
of  the  eye;  the  first  surface,  where  the  rays  of  light  are  refracted.  Some 
anatomists  have  considered  the  sclerotica  and  cornea  as  one  and  the  same, 
and  have  termed  the  cornea  the  transparent,  and  the  sclerotica  the  opaque 
cornea. 

F.  The  Aqueous  Humour,  contained  in  a  delicate  membrane  filling  the 
space  from  the  cornea  to  the  crystalline  lens.  The  space  ocoupied  by  this 
humour  is  divided  into  two  parts  by  the  iris,  forming,  as  shown  at  B,  the 
anterior  and  posterior  chambers  of  the  eye. 

G.  The  Crystalline  Lens,  contained  in  a  transparent  membrane  called  the 
Capsule,  the  principal  refracting  medium  of  the  eye.  The  capsule  adheres  by 
its  edge  to  the  ring-shaped  body  called  the  Ciliary  Circle  or  ligament,  N. 

H.  The  Vitreous  Humour,  contained  in  the  hyaloid  membrane — a  jelly- 
like  substance,  resembling  the. white  of  an  egg,  filling  the  body  of  the  eye. 

I.  The  Retina,  a  membrane  which  receives  the  impression  of  light,  and 
transmits  it  to  the  brain  through  the  optic  nerve,  K. 

j.  The  Choroid  Coat,  a  delicate  membrane  lining  the  sclerotica,  covered 
on  its  inner  surface  with  a  black  substance  ( pigmentum  nigrum ,  resembling 
the  colouring  matter  of  the  negro’s  skin)  contiguous  to  the  retina.  The  choroid, 
by  its  vascular  tissue,  serves  to  carry  the  blood  into  the  interior  of  the  eye. 

K.  The  Optic  Nerve. 

L.  Canal  of  Petit. 

M.  Central  Artery  of  the  optic  nerve. 

N.  Ciliary  Circle  or  ligament. 


THE  HUMAN  EYE. 


85 


Fig.  74. —  The  Human  Eye.  Fig.  75. — The  Eyeball ,  showing  the  Coats ,  6r-v. 
of  the  Eye.  Fig.  76. — Longitudinal  Section  of  the  Eye  and  Orbit , 
through  the  dotted  lines  on  Fig.  74. 


86 


ON  LIGHT 


O.  Ciliary  Nerves. 

P.  Vasa  Vorticosa. 

Q.  The  Ciliary  processes. 

R.  Tunica  Conjunctiva. 

R  S.  Tunica  Conjunctiva  collapsed,  as  when  the  eye  is  closed. 

S.  Elastic  Muscle  of  the  Eyelid. 

T.  Elastic  Muscle  of  the  Eye. 

U.  Superior  Oblique  Muscle. 

v.  Depressive  Muscle  of  the  Eye. 

w.  Section  of  Oblique  inferior  Muscle. 

x.  Nerves  and  Arteries. 

Y.  Tube  conveying  the  optic  nerve  to  the  brain. 

Z.  Bone  forming  the  socket  of  the  eye. 

n.b  — The  same  letters  apply  to  each  figure. 

Brewster  found  the  following  to  be  the  refractive  powers  of  the  different 
humours  of  the  eye,  the  ray  of  light  being  incident  upon  them  from  air: 


Aqueous  humour  .  .  i'336 

Crystalline  lens,  surface  i‘3767 

.  .1  ii  centre  1.3990 


Crystalline  lens,  mean  .  I  *3839 

Vitreous  humour  .  .  i'3394 

Water  ....  1  '335  8 


But  the  rays  of  light  arc  not  all  incident  upon  them  from  the  air,  and  as 
the  rays  refracted  by  the  aqueous  humour  pass  into  the  crystalline,  and  those 
from  the  crystalline  into  the  vitreous  humour,  the  indices  of  refraction  of  the 
separating  surfaces  of  their  humours  will  be — 


From  aqueous  humour  to  outer  coat  of  the  crystalline  .  roq66 
From  1:  11  to  crystalline,  using  the  mean  index  it>353 

From  vitreous  to  crystalline,  outer  coat  ....  i'oq45 

From  I.  to  n  using  the  mean  index  .  .  1.0332 

The  eye,  as  already  described,  consists  of  four  coats  or  membranes,  which 
are  disposed  in  the  following  order,  viz.,  1st,  the  sclerotic;  2nd,  the  cornea, 
which  fits  into  it  like  the  glass  of  a  watch;  3rd,  the  choroid;  and  4th,  the 
retina ;  of  two  fluids  or  humours,  the  aqueous  and  the  vitreous,  and  of  a  lens 
called  the  crystalline. 

Over  the  cornea  and  sclerotic  is  expanded  a  delicate  mucous  membrane, 
called  the  conjunctiva.  The  iris  is  suspended  across  the  eye,  and  in  its  centre 
is  an  opening,  termed  the  pupil,  which  immediately  opens  when  the  light 
diminishes,  and  closes  if  the  light  is  too  strong.  The  posterior  convexity  of 
the  lens  is  greater  than  the  anterior.  Sometimes,  from  a  too  great  convexity 
of  the  lens  or  the  cornea,  the  rays  of  light  which  enter  the  eye  come  to  a  focus 
before  they  impinge  upon  the  retina,  producing  the  defect  called  short-sighted 
vision.  Optical  science  corrects  this  inconvenience  by  the  use  of  a  concave 
lens.  If  the  crystalline  lens  is  not  sufficiently  convex,  the  rays  of  light  come 
to  a  focus  behind  the  retina ;  this  defect  is  surmounted  by  the  use  of  a  convex 
lens,  which  diminishes  the  divergence  of  the  rays.  Such  ingenious  artificial 
additions  to  the  eye  are  common  enough  at  the  present  dav,  but  it  may  b~ 
asked,  how  did  our  forefathers  bear  these  infirmities?  Spectacles  are  suppose' 
to  have  been  unknown  to  the  ancients,  and  it  is  stated  by  Francisco  Redi 
that  they  were  invented  in  the  13th  century,  between  the  years  1280  and  1311, 
probably  about  the  year  1299  or  1300;  he  gave  the  honour  of  the  discovery  to 


THE  HUMAN  EYE. 


87 


Alexander  de  Spina,  a  monk  of  the  order  of  Predicants  of  St.  Catharine,  at 
Pisa.  Muschenbroek,  the  old  electrician  who  discovered  the  Leyden  jar, 
observes  that  it  is  inscribed  on  the  tomb  of  Salvinus  Armatus,  a  nobleman 
of  Florence,  who  died  in  1317,  that  he  was  the  inventor  of  spectacles.  This 
may  have  been  the  person  who  had  the  secret  as  well  as  the  learned  monk, 
because  Redi  states  that  the  latter  only  disclosed  the  secret  upon  learning  that 
another  person  had  it  as  well  as  himself. 

Mr.  Acland  makes  the  following  practical  and  valuable  observations  on 
defects  of  vision : 

“  On  the  Symptoms  indicating  a  Necessity  for  Spectacles. 

“The  natural  decay  of  vision  occurs  usually  from  thirty  to  fifty  years  of  age, 
varying  according  to  habits  and  employment  of  the  individual.  Sometime 
during  this  interval  the  refractive  power  of  the  crystalline  humours  of  the  eye 
slightly  alters  its  condition,  whilst  the  crystalline  lens  and  cornea  change  their 
form,  so  that  a  difficulty  of  distinct  vision  is  felt.  The  eye  loses  a  portion  of 
its  power  of  seeing  at  varying  distances,  or  its  power  of  adjustment ;  and 
near  objects  are  no  longer  as  easily  seen  as  in  youth.  Reading  small  print 
by  candle-light  is  difficult,  as  the  book  requires  to  be  held  at  a  greater  distance 
from  the  eye  than  formerly,  and  a  more  powerful  light  is  needed;  and  even 
then  the  letters  appear  misty,  and  to  run  one  into  the  other,  or  seem  double. 
And  still  further,  in  order  to  see  more  easily,  the  light  is  often  placed  between 
the  book  and  the  eye,  and  fatigue  is  soon  felt,  even  with  moderate  reading. 

“  When  these  symptoms  show  the  eye  to  have  altered  its  primitive  form, 
spectacles  are  absolutely  needed.  Nature  is  calling  for  aid,  and  must  have 
assistance,  and  if  such  is  longer  withheld,  the  eye  is  needlessly  taxed,  and  the 
change,  which  at  first  was  slight,  proceeds  more  rapidly,  until  a  permanent 
injur)'  is  produced. 

“There  is  a  common  notion  that  the  use  of  spectacles  should  be  put  off  as 
long  as  possible,  but  such  is  a  great  mistake,  leading  often  to  impaired  vision 
for  life,  and  is  even  more  injurious  than  a  too  early  employment. 

“  Timely  assistance  relieves  the  eye,  and  diminishes  the  tendency  to  flat¬ 
tening,  whereas  should  the  use  of  spectacles  be  longer  postponed,  the  eye 
changes  rapidly,  and  when  the  optician  is  at  last  consulted,  it  is  found  that  a 
deeper  focus  spectacle  must  be  used  than  usual  for  the  first  pair,  and  even 
these  suit  but  a  short  time,  and  have  to  be  again  exchanged  for  those  of  still 
deeper  power;  and  these  frequent  changes  become  a  matter  of  necessity 
which,  unless  judiciously  checked,  continue  during  life. 

“  It  must  not  be  forgotten  that,  when  first  using  spectacles,  they  are  not 
required  during  daylight,  but  only  for  reading,  &c.,  by  artificial  light,  and  it 
may  be  from  six  months  to  two  years  from  the  time  of  first  adopting  them  ere 
they  will  lie  required  for  day  use. 

“  Spectacles  for  the  Short-sighted. — Shoit  sight  is  often  present  at  birth,  but 
is  little  noticed,  nor  its  inconveniences  felt,  until  study  becomes  imperative. 
When  this  occurs,  the  power  employed  should  be  always  slightly  under  that 
needed  to  remedy  the  defect,  otherwise  the  eye  will  gradually  accommodate 
itself  to  the  lenses,  and  require  constantly  an  increase  of  power.  In  all  cases 
leave  some  little  for  the  adjustment  of  the  eye  to  do,  and  then  you  may,  after 
a  time,  diminish  the  power  of  the  lenses  needed. 

“  The  Optician's  Knowledge. — Having  now  shown  when  spectacles  should 
be  employed,  let  us  for  a  moment  consider  what  are  the  requirements  that 


88 


ON  LIGHT. 


should  in  all  cases  be  possessed  by  the  optician  to  whom  the  selection  of 
spectacle  lenses  is  entrusted. 

“  These  requirements  are — 

“  ist.  An  intimate  knowledge  of  the  anatomical  structure  of  the  eye,  and 
of  the  theory  of  vision. 

“  2nd.  An  extensive  acquaintance  with  the  science  of  optics. 

“  3rd.  A  sound  mathematical  knowledge. 

“4th.  A  practical  acquaintance  with  the  manufacture  of  lenses  and 
spectacle  frames. 

“  Having  for  the  last  fourteen  years  made  the  adaptation  of  spectacles  my 
especial  study,  at  the  establishment  of  Messrs.  Horne  and  Thornthwaite,  122, 
Newgate  Street,  I  have  frequently  met  with  cases  where  great  injury  has  been 
done  to  the  weak-sighted  by  the  ordinary  optician’s  improper  selection  of 
spectacles;  and  I  could  heartily  wish  more  of  my  medical  brethren  would 
bring  their  knowledge  to  bear  on  this  subject, — which  demands,  and  frequently 
calls  forth,  all  the  science  and  skill  we  possess,  to  meet  the  requirements  of 
some  abnormal  cases  that  present  themselves.” 

The  knowledge  which  the  eye  conveys  to  the  mind  is  boundless;  the  rela¬ 
tive  condition  of  matter,  large  and  small,  of  motion  or  rest,  of  colour,  of 
solidity,  of  transparency,  of  brilliancy,  of  opacity,  of  space  or  distance,  are 
only  a  few  of  the  results  attained  by  the  exercise  of  the  faculty  of  vision. 

- ♦ - 

THE  STEREOSCOPE. 

This  most  valuable  and  instructive  instrument,  and  now  not  only  a  “house¬ 
hold  word,”  but  a  piece  of  domestic  apparatus  without  which  no  drawing-room 
is  thought  complete,  was  invented  by  Professor  Wheatstone,  and  subsequently 
modified  by  Sir  D.  Brewster.  It  demonstrates  that  man  must  have  two  eyes 
in  order  to  enjoy  the  appreciation  of  distance,  or,  like  the  fabled  Polyphemus, 
we  might  only  have  had  one  eye.  Mr.  Woodward  gives  the  following  excel¬ 
lent  and  familiar  explanation  of  the  phenomena  produced  by  the  stereoscope. 


Professor  Wheatstone’s  Reflecting  Stereoscope. 

A  familiar  explanation  of  the  phenomena  produced  by  the  Stereoscope. 

“The  name  is  derived  from  two  Greek  words,  signifying  to  view  solid  things, 
and  the  instrument  is  so  constructed  that  two  flat  pictures,  taken  under  certain 
conditions,  shall  appear  to  form  a  single  solid  or  projecting  body. 


THE  STEREOSCOPE. 


89 


“A  picture  of  any  object  is  formed  on  the  retina  of  each  eye  ;  but  although 
there  may  be  but  one  object  presented  to  the  two  eyes,  the  pictures  formed 
on  the  two  retina?  are  not  precisely  alike,  because  the  object  is  not  observed 
from  the  same  point  of  view. 

“  If  the  right  hand  be  held  at  right  angles  to,  and  a  few  inches  from,  the 
face,  the  back  of  the  hand  will  be  seen  when  viewed  by  the  right  eye  only, 
and  the  palm  of  the  hand  when  viewed  by  the  left  eye  only ;  hence  the  images 
formed  on  the  retinae  of  the  two  eyes  must  differ,  the  one  including  more  of 
the  right  side  and  the  other  more  of  the  left  side  of  the  same  solid  or  pro¬ 
jecting  object.  Again,  if  we  bend  a  card  so  as  to  represent  a  triangular  roof, 
place  it  on  the  table  with  the  gable  end  towards  the  eyes,  and  look  at  it,  first 
with  one  eye  and  then  with  the  other,  quickly  and  alternately  opening  and 
closing  one  of  the  eyes,  the  card  will  appear  to  move  from  side  to  side,  because 
it  will  be  seen  by  each  eye  under  a  different  angle  of  vision.  If  we  look  at 
the  card  with  the  left  eye  only,  the  whole  of  the  left  side  of  the  card  will  be 
plainly  seen,  while  the  right  side  will  be  thrown  into  shadow.  If  we  next  look 
at  the  same  card  with  the  right  eye  only,  the  whole  of  the  right  side  of  the 
card  will  be  distinctly  visible,  while  the  left  side  will  be  thrown  into  shadow; 
and  thus  two  images  of  the  same  object,  with  differences  of  outline ,  light  and 
shade,  will  be  formed — the  one  on  the  retina  of  the  right  eye,  and  the  other  on 
the  retina  of  the  left.  These  images  falling  on  corresponding  parts  of  the 
retina:  convey  to  the  mind  the  impression  of  a  single  object ;*  while  experience 
having  taught  us,  however  unconscious  the  mind  mav  be  of  the  existence  of 
two  different  images,  that  the  effect  observed  is  always  produced  by  a  body 
which  really  stands  out  or  projects,  the  judgment  naturally  determines  the 
object  to  be  a  projecting  body. 

“  It  is  experience  also  that  teaches  us  to  judge  of  distances  by  the  different 
angles  of  vision  under  which  an  object  is  observed  by  the  two  eyes;  for  the 
inclination  of  the  optic  axes,  when  so  adjusted  that  the  images  may  fall  on 
corresponding  parts  of  the  retina,  and  thus  convey  to  the  mind  the  impression 
of  a  single  object,  must  be  greater  or  less,  according  to  the  distance  of  the 
object  from  the  eyes. 

“  Perfect  vision  cannot  then  be  obtained  without  two  eyes,  as  it  is  by  the 
combined  effect  of  the  image  produced  on  the  retina  of  each  eye,  and  the 
different  angles  under  which  objects  arc  observed,  that  a  judgment  is  formed 
respecting  their  solidity  and  distances. 

“A  man  restored  to  sight  by  couching  cannot  tell  the  form  of  a  body  without 
touching  it,  until  his  judgment  has  been  matured  by  experience,  although  a 
perfect  image  may  be  formed  on  the  retina  of  each  eye.  A  man  with  only 
one  eye  cannot  readily  distinguish  the  form  of  a  body  which  he  had  never 
previously  seen,  but  quickly  and  unwittingly  moves  his  head  from  side  to 
side,  so  that  his  one  eye  may  alternately  occupy  the  different  positions  of  a 
right  and  a  left  eye;  and,  if  we  approach  a  candle  with  one  eye  shut ,  and  then 
attempt  to  snuff  it,  we  shall  experience  more  difficulty  than  we  might  have 
expected,  because  the  usual  mode  of  determining  the  correct  distance  is 
wanting. 

“  In  order,  then,  to  deceive  the  judgment,  so  that  flat  surfaces  may  represent 


*  That  this  is  the  coriect  theory  of  single  vision  with  the  two  eyes  is  evident  For  if,  while  looking 
at  a  single  object  with  both  exes,  we  make  a  slight  pressure  with  the  linger  on  one  of  the  eyeballs,  we 
shall  immediately  perceive  t\vo  objects;  but,  on  remoxing  the  pressure,  only  one  will  be  aga  n  seen. 


9° 


ON  LIGHT. 


solid  or  projecting  figures,  we  must  cause  the  different  images  of  a  body,  as 
observed  by  the  two  eyes,  to  be  depicted  on  the  respective  retinae,  and  yet  to 
appear  to  have  emanated  from  one  and  the  same  object.  Two  pictures  are 
therefore  taken  from  the  really  projecting  or  solid  body,  the  one  as  observed 
by  the  right  eye  only,  and  the  other  as  seen  by  the  left.  These  pictures  are 
then  placed  in  the  box  of  the  stereoscope,  which  is  furnished  with  two  eye¬ 
pieces,  containing  lenses  so  constructed  that  the  rays  proceeding  from  the 
respective  pictures  to  the  corresponding  eye-pieces  shall  be  refracted  or  bent 
outwards,  at  such  an  angle  as  each  set  of  rays  would  have  formed  had  they 
proceeded  from  a  single  picture  in  the  centre  of  the  box-  to  the  respective 
eyes,  without  the  intervention  of  the  lenses;  and  as  it  is  an  axiom  in  optics 
that  the  mind  always  refers  the  situation  of  an  object  to  the  direction  from 
which  the  rays  appear  to  have  proceeded  when  they  enter  the  eyes,  both 
pictures  will  appear  to  have  emanated  from  one  central  object;  but  as  one 
picture  represents  the  real  or  projecting  object  as  seen  by  the  right  eye,  and 
the  other  as  observed  by  the  left,  though  appearing  by  refraction  to  have  pro¬ 
ceeded  from  one  and  the  same  object,  the  effects  conveyed  to  the  mind,  and 
the  judgment  formed  thereon,  will  be  precisely  the  same  as  if  the  images  were 
both  derived  from  one  solid  or  projecting  body ,  instead  of  from  two  pictures , 
because  all  the  usual  conditions  are  fulfilled ,  and  consequently  the  two 
pictures  will  appear  to  be  converted  into  one  solid  body. 

“The  necessary  pictures  for  producing  these  effects,  excepting  those  of  geo¬ 
metrical  figures,  which  may  be  laid  down  by  certain  rules,  cannot,  however, 
be  drawn  by  the  hands  of  man ;  for,  as  Professor  Wheatstone  has  observed, 
‘  It  is  evidently  impossible  for  the  most  accurate  and  accomplished  artist  to 
delineate,  by  the  sole  aid  of  his  eye,  the  two  projections  necessary  to  form  the 
stereoscopic  relief  of  objects  as  they  exist  in  nature,  with  their  (delicate  dif¬ 
ferences  of  outline,  light,  and  shade.  But  what  the  hand  of  the  artist  was 
unable  to  accomplish,  the  chemical  action  of  light,  directed  by  the  camera, 
has  enabled  us  to  effect.’ 


“Daguerreotype  portraits  andTalbotype  pictures  are  therefore  taken, usually, 
by  two  cameras  placed  towards  the  object,  with  a  difference  of  angle  equal  to 
the  difference  of  the  angle  of  vision  of  the  two  eyes,  which  is  about  i8°  when 
the  object  is  eight  inches  from  the  eyes ;  hence,  if  these  be  carefully  examined 
and  compared  with  the  original  projecting  objects,  they  will  be  found  to  be 
faithful  representations  of  the  object  as  seen  by  each  eye  respectively.” 


PERSISTENCE  OF  VISION 


91 


Directions  for  using  the  Stereoscope. 

“The  objects  must  be  so  adjusted  in  the  box,  that  only  one  picture  may  be 
seen  in  the  centre,  care  being  taken  that  the  pictures  are  not  reversed  so  as 
to  be  seen  by  the  right  eye  instead  of  the  left,  and  vice  versa. 

“  The  proper  position  of  portraits,  buildings,  and  similar  objects  cannot  be 
mistaken ;  but  where  this  is  not  readily  perceived,  it  should  be  ascertained, 
when  the  object  can  be  marked  so  as  at  once  to  be  properly  placed. 

“The  eye-pieces,  if  allowed  to  turn,  are  marked  with  arrows,  to  indicate 
their  proper  position,  these  must  be  placed  inwards,  and  in  a  right  line  with 
each  other. 

“The  eye-pieces  in  some  instances  are  made  to  draw  out  to  suit  the  foci  of 
different  persons.  But  those  who  use  spectacles  will  generally  see  best  with 
them  on,  bringing  them  forward  so  as  to  lie  flat  on  the  eye-pieces ,  which  in 
such  cases  should  not  be  drawn  out. 

“  Persons,  however,  with  a  defective  sight  in  either  eye  will  not  be  able  to 
perceive  the  astonishing  effects  of  the  arrangement,  as  two  different  images 
will  not  be  perfectly  formed  on  the  retinae  of  the  respective  eyes.” 


FlG.  79. — Example  of  the  zigzag  path  oj  Lightning. 


PERSISTENCE  OF  VISION. 

There  is  a  most  interesting  class  of  experiments  that  depend  chiefly  upon 
another  property  or  faculty  of  vision,  by  which  we  retain  for  a  certain  limited 
period  the  images  of  objects  presented  before  us.  It  may  be  premised  that 
the  term  image  refers  to  that  picture  which  remains  upon  the  eye  as  long  as 
the  object  is  present ;  whereas  the  spectrum ,  which  every  one  knows  is  the 
Latin  for  spectre,  is  that  lingering  impression  left  upon  the  eye  after  the  leal 
object  has  been  removed.  This  property,  like  binocular  vision,  may  be 
satisfactorily  proved  in  various  ways.  1  bus,  if  a  broom-stick  be  thrust  into 
the  fire  and  burnt,  so  as  to  obtain  a  mass  of  ignited  charcoal,  and  then 
whirled  rapidly  round  in  a  circle,  a  complete  circle  of  lieht  is  visible.  Now. 


92 


ON  LIGHT. 


it  is  evident  that  the  hand  or  stick  cannot  be  in  every  part  of  the  circle 
at  the  same  instant  of  time ;  the  mind  is  therefore  obliged  to  confess,  in 
tracing  the  stick  through  the  quarter,  half,  three-quarter,  and  whole  circle, 
that  of  course  the  impression  of  the  train  of  light  must  have  remained  upon 
the  eyes,  or  else  a  single  spot  of  light  moving  in  a  circle  could  only  have  been 
visible.  A  planet,  if  it  moved  fast  enough,  would  leave  a  train  of  light, 
indicating,  like  the  burning  stick,  its  particular  path  or  disc.  The  meteors 
move  with  such  amazing  velocity  that  their  trains  of  light  are  extremely  vivid, 
marked,  and  lengthened  out,  and  show  distinctly  the  direction  or  path  they 
take.  A  discharge  of  natural  electricity  or  lightning  would,  if  it  moved  slowly, 
be  represented  by  a  ball  of  lire  travelling  from  one  point  to  another  ;  it  is, 
however,  usually  represented  by  a  lengthened-out  zigzag.  (Fig.  79.)  It  is  then 
called  “  forked  lightning,”  and  every  part  of  its  track  remaining  impressed  on 
the  vision,  the  whole  appears  as  a  series  of  continuous  lines  of  fire,  which, 
although  diverted  right  or  left,  in  a  horizontal,  perpendicular,  or  angular 
direction,  pursue  their  path  to  the  point  where  the  discharge  occurs,  they  are 
visible  as  a  whole,  and  called  a  flash  of  lightning. 

The  act  of  winking  the  eye  is  another  familiar  example  of  the  same  truth  ; 
the  eyelid  closes  and  re-opens  so  rapidly,  for  the  purpose  of  lubricating  the 
eyeball,  that  the  object  we  may  be  looking  at  does  not  become  invisible,  but 
remains  impressed  upon  the  eye.  It  has  been  ascertained  that  the  impression 
lasts  for  about  the  seventh  or  eighth  part  of  a  second,  and  although  some¬ 
times  it  may  last  for  the  third  part  of  a  second,  it  depends,  no  doubt,  upon  the 
amount  of  sensitiveness  belonging  to  the  organ  of  vision.  There  are  very 
curious  modifications  of  this  property  of  vision,  whereby  colours  and  their 
complementary  tints  are  impressed  upon  the  eye.  Thus,  if  a  red  wafer  is 
placed  on  a  sheet  of  black  paper,  and  well  illuminated  by  a  sunbeam  or  any 
brilliant  light,  it  will  appear  again  to  a  spectator  looking  from  the  black  to  a 
white  paper  as  a  green  one  ;  the  red  wafer  being  the  real  image ,  whilst  the 
green  one  is  the  spectrum.  The  experiment  may  be  varied  with  a  yellow 
wafer  on  a  black  ground,  which  appears  violet  when  the  eyes  are  turned 
rapidly  away  to  a  white  surface.  On  this  principle  a  very  entertaining  book 
has  been  published.  The  reader,  after  staring  at  one  of  the  illustrations,  is 
directed  to  look  up  to  the  ceiling  or  wall,  to  observe  the  spectral  effect.  Sir 
D.  Brewster  explains  these  curious  results,  spoken  of  as  accidental  colours,  by 
supposing  that  the  eyes,  after  staring  at  any  particular  colour,  say  a  bright 
red,  become  so  fatigued  or  partially  paralyzed  that  they  cannot  receive  or 
appreciate  the  wave  of  red  light,  but  as  white  light  is  made  up  of  various  waves 
of  coloured  light,  the  remaining  sets  of  waves — viz.,  blue  or  yellow-  can 
impress  the  vision  by  producing  the  complementary  green  colour.  The  late 
Dr.  Golding  Bird  describes  the  following  mode  of  demonstrating  this  fact, 
giving  the  merit  of  the  experiment  to  the  late  Professor  Cowper,  who  invented 
so  many  clever  illustrations  : 

“  Cut  in  a  piece  of  cardboard  a  series  of  holes,  so  that  when  folded  to¬ 
gether  they  will  exactly  correspond,  the  whole  resembling  open  lattice-work. 
Provide  some  sheets  of  thin  tissue-paper  of  various  colours,  selecting  those 
presenting  strongly  defined  tints  ;  place  one  of  them  between  the  folds  of  the 
cardboard  and  hold  it  up  to  a  vivid  light,  keeping  the  eye  fixed  on  the  lattice- 
work  whilst  the  light  penetrates  the  coloured  paper  ;  in  a  few  seconds  the 
white  colour  of  the  pasteboard  will  vanish,  and  be  replaced  by  a  strongly 
marked  tint  complementary  to  that  of  the  paper  placed  in  it.  Thus,  with 


PERSISTENCE  OF  VISION 


93 


yellow  paper  the  framework  will  appear  violet,  with  blue  it  will  be  orange,  and 
with  red  it  will  be  green.  This  illusion  is  so  complete  that  it  always  excites 
surprise  in  those  who  see  it  for  the  first  time.” 

A  little  gunpowder  placed  on  a  block  of  wood,  with  iron  filings  sprinkled 
over  it,  throws  up  a  shower  of  brilliant  sparks  of  burning  particles  of  iron 
when  fire  is  applied  ;  and  if  the  experiment  is  performed  in  a  dark  room,  and 
the  eyes  of  those  standing  near  the  experiment  are  closed  directly  after 
witnessing  the  real  image  of  the  burning  particles  of  metal,  they  will  see  a 
volume  of  faint  light,  sometimes  coloured,  which  remains  upon  the  retinae, 
and  forms  a  spectral  image.  If  the  colours  of  the  solar  spectrum  are  painted 


FlG.  8o. —  The  Polytechnic  Phenakistiscope. 


on  a  glass  disc,  to  which  rapid  motion  may  be  imparted,  after  being  fitted  into 
the  oxy-hydrogen  lantern,  a  large  disc  can  be  thrown  upon  the  screen,  which 
changes  to  a  greyish  white  directly  it  is  set  in  motion.  The  change  of  the 
disc  of  many  colours  to  a  grey  is  very  impressive,  and  is  probably  understood 
better  by  suggesting  that  the  spectator  should  look  through  an  aperture  made 
in  some  opaque  screen  at  the  coloured  disc  ;  the  red,  orange,  yellow,  green,  blue, 
indigo,  and  violet  pass  before  the  aperture  with  such  rapidity  that  they  have 
not  time  to  impress  the  retina  as  single  colours,  succeeding  each  other  one  by 
one,  and  they  must  therefore  act  collectively  on  the  vision  ;  it  collectively, 
then  synthetically  ;  or,  in  plainer  terms,  the  colours  are  caused  to  unite  and 
reconstitute  white  light,  or  the  nearest  approach  to  it  that  can  be  produced 
by  a  mechanical  contrivance  of  this  nature. 

Many  years  ago  the  juveniles  discovered  that  by  twirling  a  coin  you 
could  see  both  sides  of  it;  not  only  the  portrait  of  the  Goddess  of  Liberty, 
but  the  figure  of  the  American  eagle.  This  simple  arrangement  appears  to 
have  been  succeeded  by  an  elegant  contrivance,  invented  by  the  late  Dr. 


94 


ON  LIGHT. 


Paris,  and  called  the  Thaumatrope,  or  “Wonder-Turner,”  like  many  other 
clever  things,  a  “  nine  days’  wonder,”  and  succeeded  and  surpassed  by  a  very 
ingenious  optical  toy,  invented  by  Plateau,  called  the  Phenakistiscope. 

In  connection  with  the  name  of  Plateau,  the  Rev.  Mr.  Shaw,  in  a  letter  to  the 
writer,  says  :  “It  may  enhance  the  interest  connected  with  the  Phenakistiscope, 
if  not  known  to  you  or  your  auditory,  to  learn  that  this  gentleman,  now  re¬ 
siding  in  Ghent,  Belgium,  is  and  has  been  for  years  totally  blind,  carrying 
out  his  discoveries  and  observations  entirely  through  the  intervention  of  his 
wife.  I  mention  this  from  personal  experience,  having  assisted  him  some 
years  ago  to  translate  a  treatise  on  capillary  attraction  for  English  publica¬ 
tion.”  Plateau’s  instrument,  as  arranged  for  the  oxy-hydrogen  light  by  Soleil 
Duboscq,  is  a  very  complicated  affair,  consisting  of  the  usual  condensing 
lenses,  in  front  of  which  is  the  disc  of  glass  with  devices  in  regular  order 
painted  upon  it.  The  latter,  of  course,  rotates,  and  at  the  same  time  another 
wheel,  containing  four  double-convex  lenses  set  in  the  four  quarters  of  the 
wheel,  supplies  that  intermittent  and  separate  light  to  each  picture,  which, 
when  focused  by  the  front  lenses,  produces  all  the  effects  of  the  popular 
Zoetrope  (Fig.  81). 


If 


Fig.  8i. —  The  Zoetrope  at  rest ,  showing  Hie  simple  construction  of  the 

Instrument. 

In  order  to  produce  the  best  effect,  it  is  absolutely  necessary  that  each 
picture  should  be  impressed  separately  but  quickly  upon  the  vision ;  and 
this  is  secured  by  the  apertures  followed  by  a  certain  opaque  space,  as 
employed  in  Plateau’s  original  device  so  long  exhibited  at  the  Poly 
technic.  This  old-fashioned  apparatus  consists  of  a  wheel  perforated  with 
apertures,  on  the  back  of  which  the  figures  are  painted,  and  when  the 
spectator  looks  through  the  slits  into  a  plane  mirror  the  figures  appear  to 
move. 

It  the  figures  are  painted  in  the  usual  manner  on  a  disc,  they  all  merge  one 
into  the  other  when  the  disc  is  set  in  motion,  and  a  series  of  circles  and 
eccentrics  alone  become  apparent,  which  do  not  afford  the  slightest  idea  that 
they  represent  the  figures ;  but  Sir  Charles  Wheatstone  has  shown  that  by 
constantly  checking  the  motion,  by  a  peculiar  mechanism,  so  that  each  sepa¬ 
rate  figure  is  impressed  momentarily  on  the  vision,  then  the  same  effects  of 
motion  are  obtained  without  the  intervention  of  the  usual  revolving  slits  or 


PERSISTENCE  OF  VISION 


p1G_  g2 _ The  Zoetrope  in  motion ,  simulating  exactly  the  motions  of  a  little 

girl  playing  with  a  skipping-rope. 


aoertures.  This  important  experiment  establishes  the  basis  of  this  class  of 
illusions;  and  the  fact  is  further  proved  by  the  penny  book  now  sold  m  e 
streets.  The  little  pages  have  printed  on  them  a  series  of  devices  lepiesenti  g 
any  ordinarv  act  of  motion,  such  as  a  see-saw,  and  by  rapidly  passing  _ 
pages  over  the  thumb  with  the  first  finger  the  effect  of  apparent  movement  ts 
secured,  as  it  would  be  with  Plateau’s  apparatus,  the  Zoetrope,  or  \V heatstone  s 

disc,  with  the  checking  and  arresting  mechanism.  f 

The  best  apparatus  for  showing  to  a  large  audience  all  the  effects  ot  p 
sistence  of  vision,  and  the  curious  and  elaborate  movements  obtainable  from 
painted  discs,  is  undoubtedly  that  devised  by  Mr.  Thomas  Rose,  of  Glasgow. 
But  before  explaining  this  contrivance  it  will  be  advisable  to  study  har.  « > 

^Oneof  the  first  and  most  interesting  papers  written  on  the  effects  which  are 
produced  bv  persistence  of  vision  is  that  of  the  late  Dr.  Faraday,  and  cnt  , 
“On  a  Pecuhar  Class  of  Optical  Deceptions;”  and,  as  the  apparatus  used 
chiefly  consists  of  models  constructed  in  cardboard,  some  copious  quotations 

from  that  paper  are  here  made.t  • 

“The  preeminent  importance  of  the  eye  as  an  organ  ?f  Pc^cePtl.  ■ 
an  interest  upon  the  various  modes  in  winch  ,t  performs  its  office,  1 1 he  c, cum 
stances  which  modify  its  indications  and  the  deceptions  to  nh  nch  it  is a“cJ 
far  beyond  what  they  otherwise  would  possess.  The  following  account 


*  Fully 
and  Sons, 


described  in  article  “  Persistence  • 
London,  Glasgow,  and  Edinburgh. 


in  a  new  edition  of  the  “  Popular  Encyclopa'dia.”  Blackie 
t  “Journal  of  the  Koval  Institution,”  vol.  i  ,  p  2°5- 


96 


ON  LIGHT. 


peculiar  ocular  deception,  which,'  in  a  greater  or  smaller  degree,  is  not 
uncommon,  and  which,  if  looked  for,  may  be  observed  with  the  utmost 
facility,  may  therefore  prove  worthy  of  attention;  and  I  am  the  more  inclined 
to  hope  so,  because  in  some  points  it  associates  with  an  account  and  explana¬ 
tion  of  an  ocular  deception  given  by  Dr.  Roget  in  the  ‘Philosophical  Transac¬ 
tions’  for  1825,  page  121. 

“  The  following  are  some  cases  of  the  appearance  in  question.  Being  at  the 
magnificent  lead-mills  of  Messrs.  Maltby,  two  cog-wheels  were  shown  me 
moving  with  such  velocity  that  if  the  eye  were  retained  immovable  no  distinct 
appearance  of  the  cogs  in  either  could  be  observed ;  but,  upon  standing  in 
such  a  position  that  one  wheel  appeared  behind  the  other,  there  was  imme¬ 
diately  the  distinct,  though  shadowy,  resemblance  of  cogs  moving  slowly  in 
one  direction. 

“  Mr.  Brunei,  junior,  described  to  me  two  small  similar  wheels  at  the  Thames 
Tunnel;  an  endless  rope,  which  passed  over  and  was  carried  by  one  of  them, 
immediately  returned  and  passed  in  the  opposite  direction  over  the  other,  and 
consequently  moved  the  two  wheels  in  opposite  directions  with  great  but  equal 
velocities.  When  looked  at  from  a  particular  position,  they  presented  the 
appearance  of  a  wheel  with  immovable  radii. 

“  When  the  two  wheels  of  a  gig  or  carriage  in  motion  are  looked  at  from  an 
oblique  position,  so  that  the  line  of  sight  crosses  the  axle,  the  space  through 
which  the  wheels  overlap  appears  to  be  divided  into  a  number  of  fixed  curved 
lines,  passing  from  the  axle  of  one  wheel  to  the  axle  of  the  other,  in  form  and 
arrangement  resembling  the  lines  described  by  iron  filings  between  the  oppo¬ 
site  poles  of  a  magnet.  The  effect  may  be  obtained  at  pleasure  by  cutting  two 
equal  wheels  out  of  white  cardboard  (Fig.  83  or  84),  each  having  from  twelve 


to  twenty  or  thirty  radii,  sticking  them  on  a  large  needle  two  or  three  inches 

apart,  revolving  them  between  the  fingers,  and 
looking  at  them  in  the  right  direction  against  a 
dark  or  black  ground :  the  greater  the  velocity  of 
the  wheels,  the  more  perfect  will  be  the  appear¬ 
ance.  (Fig.  85.) 

“When  the  dark-coloured  wheel  of  a  carriage  is 
moving  on  a  good  light-coloured  road,  so  that  the 
sun  shines  almost  directly  on  its  broadside,  and  the 
wheel  and  its  shadow  are  looked  at  obliquely,  so 
that  the  one  overlaps  the  other  in  part,  then  in  the 
overlapping  part  luminous  or  light  lines  will  be 
perceived,  curved  more  or  less,  and  conjoining  the 
axle  and  its  shadow,  if  the  wheel  and  shadow  are 
superposed  sufficiently,  or  tending  to  do  so  if  they 


Fig.  85. 


PERSISTENCE  OF  VISION. 


97 


ar o  simernosed  only  in  part.  The  more  rapid  the  motion,  the  more  perfect  is 
the  appearance.  The  effect  may  be  easily  observed  (Fig.  86)  by  making  a 
pasteboard  wheel  like  one  of  those  just  described, 
blackening  it,  sticking  it  on  a  pin,  and  revolving  it 
in  the  sunshine  or  candle-light  before  a  sheet  ot 

white  paper.  .  k  _ 

“  if  the  wheel  be  converted  into  a  teetotum  or  top, 
by  having  a  pin  thrust  through  its  centre  and  spun 
upon  a  sheet  of  white  paper,  the  effect  produced  bv 

the  wheel  and  its  shadow  will  be  obtained  with  \flggS #| 

facility,  and  in  form  will  resemble  h  ig.  85.  In  all 
these  cases  no  rims  are  required;  the  spokes  01- 
radii  will  produce  the  effect.  If  a  carriage  wheel 
running  rapidly  before  upright  bars,  as  a  palisade 
or  railing,  be  observed,  the  attention  being  fixed  on 

the  wheel,  peculiar  stationary  lines  will  appear;  those  peipcndicular  to  t  c 
nave  or  axis  will  be  straight,  but  the  others  curved;  and  the  curve  will  be 
greatest  in  those  which  are  furthest  from  the  upper  straight  line  I  hese 
curves  are  the  same  in  form  as  those  already  described  and  explained  by  Dr 
Roiret  *  and  the  appearance  itself  is  produced  in  a  similar  manner ,  but  the 
pS’me  "a  are  Set,  and  the  cauL  different.  The  effect  at  presen  re¬ 
ferred  to  is  best  observed  when  the  velocities  are  great,  whereas  that  exE>htined 
bv  Dr.  Roget  takes  place  only  when  the  velocities  are  moderate.  It  is  pio- 
v' Kip  ti,at  tf,e  effects  briefly  mentioned  by  an  anonymous  writei  in  t  e 
‘Quarterly1  Journal  of 'sciencejfirst  series,  vol.  p,a83,  and  already  referred 
to  bv  Dr  Roiret,  were  of  the  kind  now. to  be  explained;  for  though  the  oe 
scription  is  not  accurate,  either  for  the  effects  which  form  the  object  of  this 
paper  or  that  explained  by  Dr.  Roget  and  is  indeed,  »ncoM«tmt  wrfh  the 
observation  or  explanation  of  any  of  the  phenomena,  it  probably  had  ts 
origin  in  the  occurVence  of  some  of  both  kinds  under  the  eyes  of  the  write.. 

-The  effect  is  easily  obtained  by  revolving  a  white  pasteboard  wheel  before 
a  black  or  dark  ground,  and  then,  whilst  regarding  the  wheel  fixedly  traversing 
the  spac“  before8!,  with  a  grate  also  cut  out  of  white  pasteboard  By  offer, ng 
the  position  of  the  grate  and  direction  of  its  motion 1  it  vvill  seen  tl  a 
straight  lines  in  the  wheel  are  always  parallel  to  the  bare  of  l the  grate a 
that  the  convexity  of  the  curved  lines  is  aiways  towards  that  side  of  the  g 
where  its  motion  coincides  in  direction  with  the  mono n  of  ^  raJ  1  - 

wheel  Bv  varying  the  velocity  of  the  wheel  and  grate,  the  curves  cnange 
dreir  appearance.  Ind  the  whole  or  any  par,  of  the  system,  as  desertbed  and 
figured  by  Dr.  Roget,  may  be  obtained  at  pleasure. 

“  I  have  had  a  very  simple  apparatus  constructed  by  *  ^  variety 

other  analogous  appearances  may  be  shown  in  great  perfection  and  variety. 
One  board  was  fixed'.., .right  upon  the  middle  of  another  sernng  as  abase;  the 
upright  board  was  cut  into  the  shape  represen  ec  g-  >  ^  little 

two  extreme  projections,  forming  points  of 

caps  cut  out  of  copper  plate  and  bent  into  s  i.qx  ?'t  '  ’  xes  onc  Qn  each 
their  places  they  offer  four  bearings  for  the  support  of  two  axes  one :  on 1  eacn 
H  mWdle?  The  axes  are  small  pieces  of  sted  wire  tapered^at  the  extr  - 
mities ;  each  has  upon  it  a  little  roller  or  disc  of  soft  wood,  which,  though 


*  “Philosophical  Transactions,”  1825,  p-  **'• 


7 


98 


ON  LIGHT. 


can  be  moved  by  force  from  one  part  of  the  axis  to  another,  still  has  friction 
sufficient  to  carry  the  latter  with  it  when  turned  round.  These  axes  are  made 
to  revolve  in  the  following  manner:  a  circular  copper  plate,  about  4  in.  in 

diameter,  has  three  pulleys  of  different  diav 
meters  fixed  upon  its  upper  surface,  whilst 
its  lower  surface  is  covered  with  a  piece  of 
fine  sand-paper,  attached  by  cement.  A  hole 
is  made  through  the  centre  of  the  plates  and 
pulleys,  and  guarded  by  a  brass  tube,  so  fitted 
as  to  move  steadily  but  freely  upon  an  up¬ 
right  steel  pin  fixed  in  the  middle  of  the  cen¬ 
tre  wooden  support ;  hence,  when  the  plate 
is  in  its  place,  it  rests  upon  the  two  rollers 
belonging  to  the  horizontal  axes,  whilst  it  is 
rendered  steady  by  the  upright  pin.  It  can 
be  easily  turned  round  in  a  horizontal  plane, 
and  it  then  causes  the  two  axes  with  their 
rollers  to  revolve  in  opposite  directions ;  and 
the  velocities  of  these  can  be  made  either 
equal  to  each  other,  or  to  differ  in  almost  any 
ratio,  by  shifting  the  rollers  upon  the  hori¬ 
zontal  axes  nearer  to  or  farther  from  the 
centre  of  the  stand. 

“To  produce  motions  of  the  axes  in  the  same 
direction,  an  aperture  was  cut  in  the  lower  part  of 
the  upright  board ;  a  roller  turned  for  it,  which 
loosely  fitted  within  the  aperture;  a  steel  pin  or  rod 
passed  as  an  axis  through  the  roller.  The  roller 
hangs  in  its  place  by  endless  lines  made  of  thread, 
passing  under  it  and  over  little  pulleys  fixed  on  the 
horizontal  axis.  When,  therefore,  it  is  turned  by  the  projecting  pin,  it  causes 
the  revolution  of  the  axes.  The  variation  in  velocities  is  obtained  by  having 
the  roller  of  different  diameters  in  different  parts,  and  by  having  pulleys  of 
different  dimensions.  This  description  will  be  easily  understood  by  reference 
to  the  figures  87  and  88. 


Fig.  88. 


“  This  apparatus  had  to  carry  wheels,  either  with  cogs  or  spokes,  which  was 
contrived  in  the  following  manner: — The  wheels  were  cut  out  of  cardboard, 
were  about  7  in.  in  diameter,  and  were  formed  with  cogs  and  sookes  at  pleasure. 


PERSISTENCE  OF  VISION 


99 


A  piece  of  cork,  being  the  end  of  a  phial  cork,  about  the  tenth  of  an  inch  in 
thickness,  was  then  fastened  by  a  little  soft  cement  to  the  middle  of  the  wheel, 
and  a  needle  run  through  both  and  then  withdrawn.  These  wheels  could  at 
any  time  be  put  upon  the  axes,  and,  being  held  sufficiently  firm  by  the  friction 
of  the  cork,  turned  with  them.  By  these  arrangements  the  axes  could  be 
changed,  or  the  wheels  shifted,  or  the  velocities  altered  without  the  least  delay. 

“  The  beauty  of  many  of  the  effects  obtained  by  this  apparatus  has  induced 
me  to  describe  it  more  particularly  than  I  otherwise  should  have  done.  The 
appearance  which  I  first  had  shown  to  me  by  Mr.  Maltby  was  exhibited  very 
perfectly :  two  equal  cog-wheels  were  mounted  (Fig.  89)  so  as  to  have  equal 
opposite  velocities;  when  put  into  motion,  which  is  easily  done  by  the  thumb 
and  finger  applied  to  the  upper  pulley  and  the  horizontal  copper  plate,  they 
presented  each  the  appearance  of  an  uniform  tint  at  the  part  corresponding  to 
the  series  of  cogs  or  teeth,  provided  that  the  eye  was  so  placed  as  to  see  the 
whole  of  both  wheels;  but  when  a  position  was  taken  up  so  that  the  wheels 
were  visually  superposed,  then,  in  place  of  an  uniform  tint,  the  appearance  of 
teeth  or  cogs  were  seen,  misty,  but  perfectly  stationary,  whatever  the  degree 
of  velocity  given  to  the  wheel.  By  cutting  the  cogs  or  teeth  in  the  wheel  nearest 
to  the  eye  deeper  (Fig.  90),  the  eye  could  be  brought  into  the  prolongation  of 
the  axes  of  the  wheels,  and  then  the  spectral  cog¬ 
wheel  appeared  perfect  (Fig.  91).  The  number  of 
intervals  thus  occurring  was  exactly  double  the 
number  of  teeth  in  either  wheel ;  thus  a  wheel  with 
twelve  teeth  produced  twenty-four  black  and 
twenty-four  white  alternations.  When  one  wheel 
was  made  to  move  a  little  faster  than  the  other,  by 
shifting  the  wooden  roller  on  its  axis,  then  the 
spectrum  travelled  in  the  direction  of  that  wheel 
having  the  greatest  velocity,  and  with  more  rapi¬ 
dity  the  greater  the  difference  between  the  velocities 
of  the  two  wheels.  When  the  wheels  were  looked 
at  so  that  they  only  partly  visually  superposed  each 
other,  the  effect  took  place  only  in  those  parts; 
and  it  was  striking  and  extraordinary  to  observe,  as  it  were,  two  uniform  tints 
mingling  and  instantly  breaking  out  into  the  alternations  of  light  and  shade 
which  I  have  described.  There  are  many  variations  in  the  curvature  and  other 
appearances  obtained  by  altering  the  position  of  the  eye,  which  will  be  imme¬ 
diately  understood  when  observed,  and  which,  for  brevity’s  sake,  1  refrain  from 
describing. 

“  Wheels  were  then  fixed  on  the  machine,  consisting  of  radii  or  spokes,  each 
having  twelve,  equal  in  length  and  width  (Fig.  84).  When  revolving  alone, 
each  wheel  gave  with  a  certain  velocity  a  perfectly  uniform  tint ;  but  when 
visually  superposed  there  appeared  a  fixed  wheel,  having  twenty-four  spokes, 
equal  in  dimensions  to  the  original  spokes.  Variations  of  the  position  of  the 
eye,  or  of  the  relative  velocity  of  the  two  wheels,  caused  alternations  similar 
to  those  I  have  referred  to  with  the  cog-wheels. 

“  In  observing  these  effects,  either  tiie  wheels  should  be  black  or  in  shade, 
whilst  the  part  beyond  is  illuminated  ;  or  else  the  wheels  should  be  white  and 
enlightened,  whilst  the  part  beyond  is  in  deep  shade.  The  cog-wheels  present 
nearly  a  similar  appearance  in  both  cases,  though  in  reality  the  parts  of  the 
spectrum  which  appear  darkest  by  one  method  are  lightest  by  the  other.  The 

7 — 2 


Fig.  91. 


TOO 


ON  LIGHT. 


spoke-wheels  give  a  spectrum  having  white  radii  in  the  first  method,  and 
dark  radii  in  the  second.  Placing  the  wheels  between  the  eye  and  the  clouds, 
on  a  white  wall,  or  a  lunar  lamp,  answers  very  well  for  the  first  method  ;  and, 
for  the  second,  merely  reversing  the  position,  and  allowing  the  light  to  shine 
on  the  parts  of  the  wheel  towards  the  eye,  whilst  the  background  is  black  or 
in  obscurity,  is  all  that  is  required.  Strictly,  the  phenomena  should  be  viewed 
with  one  eye  only,  but  it  is  not  often  that  vision  with  two  eyes  disturbs  the 
effects  to  any  extent. 

“  The  cause  of  these  appearances,  when  pointed  out,  is  sufficiently  obvious, 
and  immediately  indicates  many  other  effects  of  a  similar  kind,  and  equally 
striking,  which  are  dependent  upon  it.  The  eye  has  the  power,  as  is  well 
known,  of  retaining  visual  impressions  for  a  sensible  period  of  time  ;  and  in 
this  way  recurring  actions,  made  sufficiently  near  to  each  other,  are  percep¬ 
tibly  connected  and  made  to  appear  as  a  continued  impression.  The  lumi¬ 
nous  circle  visible  when  a  lighted  coal  or  taper  is  whirled  round,  the  beautiful 
appearance  of  the  Kaleidophone,  the  uniform  tint  spread  by  the  revolution  of 
one  of  the  spoke  or  cog  wheels  already  described,  are  few  of  the  many  effects 
of  this  kind  which  are  well  known. 

“  But  during  such  impressions  the  eye,  although  to  the  mind  occupied  by 
an  object,  is  still  open,  for  a  large  proportion  of  time,  to  receive  impressions 
from  other  sources  ;  for  the  original  object  looked  at  is  not  in  the  way  to  act 
as  a  screen,  and  shut  out  all  else  from  sight.  The  result  is  that  two  or  more 
objects  may  seem  to  exist  before  the  eye  at  once,  being  visually  superposed. 
The  school-boy  experiment  of  seeing  both  sides  of  a  whirling  halfpenny  at  the 
same  moment,  the  appearance  of  the  Thaumatrope,  and  the  transparency  of 
the  revolving  cog  or  spoke  wheels  referred  to — in  consequence  of  which  other 
objects  are  seen  through  the  shaded  parts — are  all  effects  of  this  kind  ;  two 
or  more  distinct  impressions,  or  sets  of  impressions,  being  made  upon  the 
eye,  but  appearing  to  the  perception  as  one. 

“So  it  is  in  the  appearances  particularly  referred  to  in  this  paper.  They 
are  the  natural  results  of  two  or  more  impressions  upon  the  eye,  really,  but 
not  sensibly,  distinct  from  each  other.  If,  whilst  the  eye  is  stationary,  a 
series  of  cogs,  like  those  represented  by  the  continuous  outline  (Fig.  92),  pass 

rapidly  before  it,  they  produce  a  uniform 
tint  to  the  eye  ;  and,  for  the  purpose  of 
following  out  the  description,  let  it  be 
supposed  the  cogs  are  in  shade  between 
the  eye  and  a  white  background,  the  tint 
is  then  a  hazy  semi-transparent  grey.  If 
another  series  of  cogs,  represented  by  the 
dotted  outline,  and  close  to  the  first,  so 
as  to  give  no  sensible  angular  difference 
to  the  dimensions  of  the  cogs,  pass  with 
equal  velocity  in  the  same  direction,  it  will  produce  its  corresponding  tint. 
If  the  two  sets  of  cogs  be  visually  superposed  in  part,  as  in  the  figure,  there 
will  be  no  alteration  in  the  uniformity  of  the  tint.  If  the  cogs  of  one  set  be 
more  or  less  to  the  right  or  left  of  the  other,  then  the  superposed  part  will 
approach  more  or  less  to  the  tint  of  the  shaded  and  uncut  part  of  the  card¬ 
board  wheel,  and  be  less  transparent.  But  if,  instead  of  the  motion  being 
equal,  the  velocities  are  unequal,  then  total  changes  of  the  appearance  super¬ 
vene;  the  spectrum  (if  I  may  so  call  it)  of  the  superposed  parts  becomes  alter- 


PERSISTENCE  OE  VISION 


ioi 


nately  light  and  dark,  and  the  alternations  take  place  more  or  less  rapidly  as 
the  velocities  of  the  two  sets  of  cogs  differ  more  or  less  from  each  other. 

“  When  the  cogs  move  in  opposite  directions,  the  uniform  tint  which  each 
alone  can  produce  is  soon  broken  up  in  the  superposed  parts  into  lighter  and 
darker  portions  ;  and  when  the  velocities  of  both  are  equal,  the  spectrum  is 
resolved  into  a  certain  number  of  light  and  dark  alternations,  which  are 
perfectly  fixed,  and  which  to  the  mind  offer  a  singular  contrast  to  the  rapidly 
moving  state  of  the  wheels,  and  to  the  variations  which  their  velocity  may 
undergo  without  altering  the  visible  result. 

“The  effect,  strange  as  it  at  first  appears,  will  be  easily  understood  by 
reference  to  Fig.  91.  Suppose  the  eye  directed  to  the  part  /  beyond  the  cogs, 
and  the  sets  of  cogs' to  be  moving  with  equal  velocities  in  opposite  directions, 
indicated  by  the  arrow-heads,  the  part  /  will  be  eclipsed  by  the  cogs  a  and  b 
simultaneously,  and  for  exactly  the  same  time ;  for  they  begin  to  cover  it  and 
leave  it  together.  /,  therefore,  is  alternately  open  to  and  shut  from  the  eye 
for  equal  times  ;  for  what  these  cogs  have  done  will  be  performed  by  all  the 
other  cogs  in  turn,  and  the  cogs  are  equal  in  area  to  the  spaces  between  ; 


Fig.  92  A. 


Fig.  92  b. 


half  the  light,  therefore,  from  that  part  of  the  background  comes  to  the  eye, 
and  produces  a  corresponding  impression.  But  with  respect  to  the  point  1 , 
although  the  cog  b  is  just  leaving  it  exposed,  the  cog  a  is  just  beginning  to 
eclipse  it ;  and  by  the  time  the  latter  has  passed  over,  the  edge  ol  the  cog  e 
will  be  upon  the  spot,  and  that  cog  will  therefore  hide  it  until  J  comes  up,  so 
that  in  fact  the  point  d  is  always  hidden  ;  no  light  comes  Irom  that  part  of 
the  background,  and  it  consequently  appears  dark.  /  is  circumstanced  just 
as  /  was,  for  the  cogs  a  and  e  cover  it  simultaneously,  and  so  do  all  the  ot  u/ 
cogs  in  pairs  ;  it  is,  therefore,  a  light  space  in  the  spectrum,  d'  is  a  repetition 
in  everything  of  d,  and  is  a  dark  space.  The  parts  intermediate  between  the 
maxima  of  light  and  darkness  will,  by  examination,  be  found  to  be  eclipsed 
for  intermediate  periods,  and  to  appear  more  or  less  dark  in  consequence,  so 
that  the  appearance  of  the  spectrum  belonging  to  the  visually  superposed 
parts  of  the  two  sets  of  cogs  is  as  in  Fig.  92  A.  ,  , 

“  In  the  case  of  equal  wheels  with  radii,  the  fixed  spectrum  produced  when 
the  wheels  superpose  each  other  has  twice  the  number  of  radii  of  cither 
wheel,  that  being,  of  course,  the  number  of  times  which  the  radii  coincide 

with  each  other  in  one  revolution.  ,  .  , 

“  Fig.  92  B  represents  the  fixed  spectrum  produced  by  two  equal  wheels  of 
eight  radii  each.  When  the  radii  or  spokes  are  narrow,  the  difference  in  the 
intensity  of  tint  between  the  middle  and  the  edges  of  each  image  of  a  spoke 
is  so  slight  as  to  be  scarcely  perceptible.  But  as  this  circumstance  and  many 
others  will  explain  themselves  immediately  they  are  experimentally  observed, 


102 


ON  LIGHT. 


it  is  unnecessary  to  dwell  minutely  upon  them  here.  A  very  simple  experi¬ 
ment  will  render  the  whole  of  these  effects  perfectly  intelligible. 

“  If  a  little  rod  of  white  cardboard,  five  or  six  inches  long,  and  one-thirtieth 
of  an  inch  wide,  be  moved  to  and  fro  from  right  to  left 
before  the  eye,  an  obscure  or  black  background  being 
beyond,  it  will  spread  a  tint,  as  it  were,  over  the  space 
through  which  it  moves.  (Fig.  93,  A.)  A  similar  rod 
held  and  moved  in  the  other  hand  will  produce  the 
same  effect  ;  but  if  these  be  visually  superposed,  i.e.,  if 
one  be  moved  to  and  fro  behind  the  other,  also  moving, 
then  in  the  quadrangular  space  included  within  the  in¬ 
tersection  of  the  two  tints  will  be  seen  a  black  line, 
sometimes  straight,  and  connecting  the  opposite  angles 
of  the  quadrangle,  at  other  times  oval  or  round,  or  even 
F IG.  93.  square,  according  to  the  motions  given  to  the  two  card¬ 

board  rods  (Fig.  94,  n).  . 

“This  appearance  is  visible  even  when  the  rods  are  several  inches  or  a  foot 
apart  from  each  other,  provided  they  are  visually  superposed.  It  is  produced 
exactly  as  in  the  former  case,  and  the  black  line  is  in  fact  the  path  of  the 
intersecting  point  of  the  moving  rods.  As  their  motions  vary,  so  does  the 
course  of  this  point  change,  and,  wherever  it  occurs,  there  is  less  eclipse  of 
the  background  beyond  than  in  the  other  parts,  and  consequently  less  light 
from  that  spot  to  the  eye  than  from  the  other  portions  of  the  compound  spec¬ 
trum  produced  by  the  moving  rods. 

“In  this  experiment  the  eye  should  be  fixed,  and  the  part  looked  at  should 
be  between  the  planes  in  which  the  rods  are  moved.  The  variation  produced 
by  using  black  rods,  and  looking  at  a  white  ground,  will  suggest  itself.  Those 
who  find  it  difficult  to  observe  the  effect  at  first,  will  instantly  be  able  to  do 
so  if  the  rod  nearest  the  eye  is  black,  or  held  so  as  to  throw'  a  deep  shade — - 
the  line  is  then  much  more  distinct;  but  the  explanation  is  not  quite  the  same, 
but  nearly  so — it  will  suggest  itself.  Twro  bright  pins  or  needles  produce  the 
effect  veiy  well  in  diffused  daylight;  and  the  line  produced  by  the  shadow  of 
one  on  the  other,  and  that  belonging  to  the  intersection,  are  easily  dis¬ 
tinguished  and  separated. 

“If  whilst  a  single  bar  is  moved  in  one  hand  several  bars  or  a  grate  is 
moved  in  the  other,  then  spectral  lines,  equal  to  the  number  of  bars  in  the 
grate,  are  produced.  If  one  grate  is  moved  before  another,  then  the  lines  are 
proportionably  numerous  ;  or  if  the  distances  are  equal,  and  the  velocity  the 
same,  so  that  many  spectral  lines  may  coincide  in  one,  that  one  is  so  much 
the  more  strongly  marked.  If  the  bars  used  be  serpentine  or  curved,  the  lines 
may  be  either  straight  or  curved  at  pleasure,  according  as  the  positions  and 
motions  are  arranged  so  as  to  make  the  intersecting  point  travel  in  a  straight, 
or  a  curve,  or  in  any  other  line. 

“  The  cause  of  the  curious  appearance  produced,  when  spoke  or  cog  wheels 
revolve  before  each  other,  already  described,  will  now  be  easily  understood  ; 
the  spokes  and  cogs  of  the  w'heels  produce  precisely  the  same  effect  as  the 
bars  held  in  the  hand,  and  the  fixedness  of  the  position  of  the  spectrum 
depends  upon  the  recurrence  of  the  intersecting  or  hiding  positions,  exactly  in 
the  same  place  with  equal  wheels,  provided  the  opposite  motion  of  each  be  of 
equal  velocity  and  the  eye  be  fixed. 

“  When  the  wheels  were  used  in  the  little  machine  described  (Fig.  87),  having 


io3 


PERSISTENCE  OF  VISION 


equal  but  oblique  teeth,  and  the  obliquity  in  the  same  direction,  the  spectrum 
was  also  marked  obliquely  ;  but  when  the  obliquity  was  in  opposite  directions 
the  spectrum  was  marked  as  with  straight  teeth. 

“  When  equal  wheels  were  revolved  with  opposite  motions,  one  rather  faster 
than  the  other,  the  spectrum  travels  slowly  in  the  direction  of  the  fastest  wheel ; 
when  the  difference  in  the  velocity  of  the  two  wheels  was  made  greater,  the 
spectrum  travels  faster.  These  effects  are  the  necessary  consequence  of  the 
transference  of  the  intersecting  points  already  described,  in  the  direction  of 
the  motion  of  the  fastest  wheel.  When  one  wheel  contains  more  cogs  than 
the  other,  as,  for  instance,  twenty-four  and  twenty-two,  then  with  equal 
motions  the  spectrum  was  clear  and  distinct,  but  travelled  in  the  direction  of 
the  wheel  having  the  greatest  number  of  teeth. 

“  When  the  other  wheel  was  made  to  move  so  much  faster  as  to  bring  an 
equal  number  of  cogs  before  the  eye,  or  rather  any  one  part  of  the  eye,  in  the 
same  time  as  the  other,  the  spectrum  became  stationary  again.  The  explana¬ 
tion  of  these  variations  will  suggest  themselves  immediately  the  effects  are 
witnessed.  When  the  motion  of  the  wheels  upon  the  machine  is  in  the  same 
direction,  the  velocities  equal,  and  the  eye  placed  in  the  prolongation  of  the 
axis  of  the  wheels,  no  particular  effect  takes  place.  If  it  so  happens  that  the 
cogs  of  one  coincide  with  those  of  the  other,  the  uniform  tint  belonging  to  one 
wheel  only  is  produced.  If  they  project  by  the  side  of  each  other,  it  is  as  if 
the  cogs  were  larger,  and  the  tint  is  therefore  stronger.  But,  when  the  velo¬ 
cities  vary,  the  appearances  are  very  curious;  the  spectrum  then  becomes 
altogether  alternately  light  and  dark,  and  the  alternations  succeed  each  other 
more  rapidly  as  the  velocities  differ  more  from  each  other. 

“  When  wheels  with  radii  are  put  upon  the  machine,  it  is  easy  to  observe, 
in  perfection,  the  optical  appearance  already  referred  to,  as  exhibited  by  car¬ 
riage-wheels,  &c.  (Fig.  85).  They  should  be  looked  at  obliquely,  so  as  to  be 
visually  superposed  only  in  part ;  and,  provided  the  wheels  are  alike,  and  both 
revolving  in  the  same  direction  with  equal  velocities,  they  immediately  assume 
the  form  described,  passing  in  curves  from  the  axis  of  one  wheel  to  the  axis 
of  the  other,  much  resembling  in  disposition  those  curves  formed  by  iron 
filings  between  two  opposite  poles  of  a  magnet. 

“  If  the  wheels  revolve  in  opposite  directions,  then  the  spectral  lines,  origi¬ 
nating  at  each  axis  as  a  pole,  have  another  disposition,  and,  instead  of  running 
the  one  set  into  the  other,  are  disposed  generally  like  the  filings  about  two 
similar  magnetic  poles,  as  if  a  repulsion  existed ;  not  that  the  curves  or  the 
causes  are  the  same,  but  the  appearances  are  similar.  A  very  little  attention 
will  show  that  all  these  lines  are  the  necessary  consequence  of  the  travelling 
of  successive  intersecting  points;  and  any  one  of  them  may  be  followed  out 
by  experimenting  with  the  two  pasteboard  rods  already  described,  these  being 
moved  in  the  hand  as  if  each  were  the  spoke  of  a  wheel. 

“All  these  effects  may  be  simply  exhibited  by  cutting  out  two  equal  paste¬ 
board  wheels  without  rims,  passing  a  pin  as  an  axis  through  each,  spinning 
one  upon  a  mahogany  or  dark  table,  and  then  spinning  the  other  between  the 
fingers  over  it,  so  that  the  two  may  be  visually  superposed.  If  the  appear¬ 
ances  are  observed  by  a  lamp  or  candle,  the  wheels  should  be  so  held  to  the 
light  that  the  shadow  of  the  upper  may  not  fall  upon  the  lower;  otherwise  the 
effects  are  complicated  by  similar  sets  of  lines  which  appear  upon  the  lower 
wheel,  and  are  produced  by  the  shadow  of  the  upper. 

“These  are  the  same  in  form  and  disposition  as  in  the  former,  and  are  even 


ON  LIGHT. 


IO  + 


more  distinct  ;  they  should  be  viewed,  not  through  the  upper  wheel,  but 
directly  upon  the  lower;  their  explanation  has  in  part  been  given,  and  will  be 
sufficiently  evident.” 

Returning  to  the  consideration  of  Mr.  Rose’s  Photodrome,  or  “  Light- 
Runner,”  the  construction  is  simple,  and  not  likely  to  get  out  of  order. 

It  consists  of  two  parts.  The  first  part  ( b ,  Fig.  94)  consists  of  a  wheel  about 
four  feet  in  diameter,  provided  with  eight  spokes,  and  wholly  constructed  of  the 
the  best  seasoned  mahogany.  The  wheel  is  driven  by  a  gut  band  proceeding 
from  a  smaller  flying-wheel,  which  is  worked  by  hand.  This  large  wheel  is  so 


Fig.  94. —  The  two  portions  of  Rose’s  Photodrome,  viz.,  the  large  and  s?nall 

wheels  alluded  to. 

arranged  on  a  platform,  or  other  convenient  place,  that  a  strong  light,  arranged 
in  a  lantern  with  a  proper  lens,  casts  its  ravs  through  one  of  two  apertures 
in  a  second  disc  {a,  Fig.  94),  about  two  feet  in  diameter,  placed  below  and  in  front 
of  it,  so  that  the  shadow  of  the  large  wheel  is  distinctly  thrown  upon  the  white 
screen  behind.  When  the  large  wheel  is  set  in  motion,  and  a  certain  velocity, 
from  about  250  to  300  revolutions  per  minute,  obtained,  all  the  spokes  and  the 
shadows  of  them  disappear,  and  then  the  curious  effect  of  the  rim  or  ring  of 
the  wheel  is  shown  revolving  without  any  apparent  connection  with  the  central 
axis.  Whilst  this  large  wheel  is  going  round,  if  the  spectator  looks  obliquely 
through  the  spokes  of  the  real  wheel  to  those  of  the  shadow-wheel,  he  will  see 
the  curved  lines  described  by  Faraday,  as  obtained  by  him  with  his  cardboard 
models  in  Fig.  86,  p.  77.  In  a  favourable  position  the  whole  distorted  shadow- 
wheel,  with  curve  lines  on  a  grey  ground,  becomes  visible  on  a  scale  not 
probably  contemplated  by  Faraday  with  his  small  cardboard  spokes. 

These  effects  being  shown  with  the  large  wheel,  attention  is  now  directed  to 
the  second  portion  of  the  apparatus,  consisting  of  a  disc  about  two  feet  in 


PERSISTENCE  OF  VISION.  105 


diameter,  and  provided  with  two  apertures.  With  an  ingenious  sliding 
arrangement  six  or  eight  apertures  can  be  obtained,  if  required,  but  two  aie 
preferred  for  this  experiment. 

V  The  rays  of  light,  as  already  described,  pass  through  these  apertuies  every 
time  they  come"  round,  and  the  large  wheel  being  still  in  motion  and  the 
spokes  invisible,  directly  the  small  disc  begins  to  move  and  attains  a  moderate 
velocity  all  the  spokes  and  their  shadows  return.  At  first  they  are  very  hazy 
and  indistinct,  and  almost  semi-transparent;  but  as  the  velocity  increases 
they  become  distinctly  apparent,  and  the  large  wheel  appears  to  be  go 
round  slowly  and  nearly  to  stand  still.  The  nest  change  m  the  veloe tty  of 
the  small  disc  throwing  the  flashes  causes  the  spokes  to  ^e  multiphed, 
generally  by  five;  thus,  forty  spokes  and  forty  shadows  may  be  cou"ted’ ^ ■ 
latter  being  grey,  and  not  black,  like  the  original  eight  shadows.  The  next 
an, I  last  incase’ of  velocity  in  the  small  disc  wh.ch  bnngs  ,t  up  to  aW  a 
thousand  revolutions  in  a  minute,  causes  the  large  w  ice  »  ,  .  . 

and  eight  shadows-to  appear  quite  distinct,  and  at  that  moment  although 
the  large  wheel  is  going  round  three  hundred  times  in  a  minute,  it  appea  . 

‘^The  flashes  of  light  perform  the  same  duty  as  the  slits ‘  ^tKeht 
Plateau’s  apparatus,  and  before  the  large  wheel  has  time  ^ 

arrives  and  passes  away.  If  the  large  wheel  was  moving  a  difference 

thousand  revolutions  in  a  minute,  no  change  would  occur.  ...  . 

in  the  two  velocities  which  determines  this  curious  form  of  the  illusion 
Mr.  Rose  mentions  a  most  amusing  story  in  connection  \u  tj 

illusions  produced  by  the  Photodrome,  viz.,  that  of  the  large  wheel  appa ren «y 
standing  still  when  it  is  really  moving  very  fast.  It  appears  that  whilst 


io6 


ON  LIGHT. 


nn.eXfPHriment  to,a  nu?ber  of  workinS  men-  at  a  lecture-hall  in 
Glasgow,  one  of  them  rose  from  his  seat,  and  wanted  to  creep  up  quietly  to 

the  large  wheel,  for  the  purpose  of  convincing  himself  by  touch  that  it  reallv 

bablv  h3g'  °rtHUnamIy’  ?ey  S^)pped  the  man  in  time>  or  he  would  pro¬ 
bably  have  received  a  blow  from  the  spokes  of  the  wheel  which  might  have 

hnger-bones.  This  incredulity  was  an  interesting  example  of 

the  effect  of  that  teaching  which  grows  up  with  us,  viz,  that  “seeing  is 

believing.  Here  was  a  man  who  had  evidently  never  seen  an  optical  illusion 

before,  and  doubtless,  by  the  time  Mr.  Rose  had  finished  his  beautiful  ex 

penments,  he  discovered  that  the  eye,  like  the  ear,  is  easily  deceived. 

Ga  a'ithe  fm'Vent  en?ineer  of  Greenwich,  has  since  invented  a  most 
“  ThS  n  an^  auf  hable  application  of  the  same  principle  of  persistence,  called 
workeonaLGhf  Ske  et0n’”  which  the  writer  has  described  in  another  popular 


LIGHT  AND  COLOUR. 


SPECTRUM  ANALYSIS. 

Aberration  and  Achromatism. 

,  beautiful  and  wonderfully  ingenious  apparatus  now  employed  by 
chermsts  and  astronomers  for  spectrum  analysis,  with  its  electric  lamps,  and 
Sir  and  prisms,  is  a  great  contrast  to  the  simple  means  emplove’d  by 

Sn  Isaac  Newton,  nearly  two  hundred  years  ago,  to  effect  the  same  object,  viz  , 
the  decomposition  of  light.  The  great  discovery  made  by  Newton,  about  the 

fished  bvth  T  l  '§hf  'S  n0t  °/a  S'mpI1  but  of  a  comPound  nature,  was  estab- 
shed  b>  t  he  help  of  a  prism  (an  optical  instrument  already  described  at  p.  ;c) 

thi ough  which  a  sunbeam  was  permitted  to  pass.  No  doubt,  whilst  moving  the 

discovered  t,'s  ^  prK°dllcdon  of  colour  might  have  been  accidentally 

fn  tT3d\  would  have  been  by  any  other  careful  experimentalist;  but  it 
foi  tunately  happened  that  the  discovery  fell  to  the  lot  of  a  mind  already  well 
prepaied  to  grapple  with  difficult  phenomena,  and  Newton  was  soon  able  to 
convmce  h.mself  and  others  tha,  he  had.analysed  light,  and  resolved  U  imo 
seven  colours— viz.,  Red,  Orange,  Yellow,  Green,  Blue,  Indigo,  and  Violet 
Here  was  light,  not  only  refracted  or  bent  from  its  natural  course,  but  spread 
out  a  phenomenon  to  which  the  term  dispersion  is  now  given.  Other  lenses 
an d  enro  'ostru men ts  possess  the  same  property  in  a  more  limited  degree, 
tbT m  w  ithGf  edgGf  °f  th?  pictures  or  images  thrown  by  convex  lenses  from 

d  saiegLh  !‘^rnr  10W  <iolourS-  *n  what  are  called  achromatic  lenses,  the 
sagrerable  effect  upon  the  eye  produced  by  ordinary  lenses  is  prevented,  and 

the  colours  n-utrafi^etl  and  destroyed.  The  value  of  science  teaching  as  a 
m  Sula;educa“on  is  now  fully  recognized;  but  schoolmasters  have  little 
?  superintend  the  manufacture  and  collection  of  oxygen  in  bags, 
oxv-ralri  °&e-  If1  a  ,vo  taic  battery,  for  the  purpose  of  obtaining  either  the 
only  taimhf1  then  en tnC  'gbJ  ’  consequently,  the  phenomena  of  light  are 
the  le  w  m  r  nb  fCa  /  mstead  of  experimentally,  if  a  master  could  teach 
alloS  ag^nBeip  eS f°f  °PtlCS  by  mfrely  clos,n-  the  shutters  of  his  room,  and 

sized  dTanhnamf1!  of  a  -reater  oi;  lesscr  diameter,  determined  bv  different¬ 
sized  diaphiagms,  to  enter  through  an  aperture  into  the  darkened  room,  he 


LIGHT  A  A/D  COLOUR. 


107 


The  Heliostat,  placed  on  a  shelf  outside  the  window,  reflecting  the  ray  of 
light  which  passes  through  a  hole  in  a  shutter  on  to  a  prism,  to  show  the 
decomposition  of  light. 


would  be  more  disposed  to  impart  this  kind  of  knowledge  to  his  boys,  because 
the  sunbeam  would  cost  nothing,  and  with  the  help  of  an  instrument  called 
the  Heliostat*  the  sun,  and  erraros,  to  stand  still)  the  reflected  ray  of 

light  may  always  be  retained  in  a  fixed  direction,  notwithstanding  the  apparent 
motion  of  the  sun. 

Silbermann’s  Heliostat,  constructed  by  Duboscq,  of  Paris,  is  perhaps  one 
of  the  most  perfect  instruments  of  the  kind. 

This  apparatus,  as  its  name  indicates,  is  used  for  the  purpose  of  directing  a 
ray  of  light  in  one  fixed  direction,  or  on  one  particular  fixed  place  or  point. 
It  is  constructed  essentially  of  a  triangular  foot,  a  clock,  and  a  mirror. 

i°.  The  triangular  and  horizontal  foot,  T  T  T,  is  furnished  with  screws  for 
levelling  the  whole  instrument. 

About  the  axis,  passing  through  the  centre  of  the  foot,  a  horizontal  disc 
turns,  which  carries  a  spirit-level,  N,  and  upon  which  also  are  fixed  the  vertical 
supports  of  the  clock  and  the  mirror. 

The  disc  is  fixed  in  any  position  by  means  of  the  binding-screw,  v,  placed 
on  one  of  the  rays  of  the  triangular  foot,  T. 

2°.  The  clock,  H,  can  swing  about  a  line  always  horizontal,  and  commum- 


FlG.  96. 


*  These  instruments  are  now  sold  at  a  very  cheap  rate,  and  can  be  obtained  for  from  $15. 00  to 

$->500. 


io8 


ON  LIGHT. 


cates  a  movement  of  rotation  on  itself  to  the  axis,  A,  of  the  heliostat  and  to  its 
appendages.  The  clock  beats  the  quarters  of  a  second  ;  on  its  upper  cover 
are  two  hands,  a  a,  which  move  round  their  respective  dials  :  the  first  in 
one  hour,  the  second  in  one  minute.  A  movable  index  in  a  groove,  which 
approaches  the  letter  A  and  recedes  from  K,  is  introduced  to  correct  the  clock 
when  it  is  too  fast  or  too  slow. 

A  button,  b,  is  placed  above  one  of  the  dial-plates,  and  whose  index  places 
itself  by  turns  on  the  letter  A,  or  on  the  letter  M,  and  thus  serves  to  stop 
the  clock  or  to  set  it  going.  An  arc  divided  vertically,  L  I J,  called  the  “arc 
of  latitude,”  is  fixed  to  the  horizontal  axis,  about  which  the  clock  moves,  and 
brings  the  axis  A  of  the  heliostat  in  the  direction  of  the  earth’s  axis. 


Fic».  g. — Silbermann's  Heliostat. 


The  axis  ot  the  heliostat  moves  in  a  double  cylindical  envelope,  and  turns 
round  once  in  24  hours  and  carries  at  the  top  a  cubical  box,  B,  which  it  can 
move  in  its  rotation.  The  cubical  box  in  turning  carries  a  pointer  to  mark 
the  true  time  on  a  dial,  C  c',  fixed  to  the  exterior  envelope  of  the  axis,  and  per¬ 
pendicular  to  this  axis.  Across  the  cubical  box  moves  again  parallel  to  the 
axis  an  arc,  D  d',  called  the  “  arc  of  declination,”  and  which  is  divided  on  one 
side  in  degrees,  and  on  the  other  in  days  and  months. 

In  order  that  the  heliostat  may  adapt  itself  to  all  latitudes,  it  is  necessary 
that  the  arc  of  declination  shall  take  every  possible  position.  The  exterior 
envelope  of  the  axis  of  the  heliostat  carries  a  second  cubical  box,  b',  which 
turns  about  the  axis  and  also  carries  in  its  rotation  the  arc  of  reflection,  R 
which  crosses  it,  and  which  may  be  raised  or  depressed  by  sliding  it  in  the  box. 


LIGHT  AND  COLOUR. 


109 


30.  The  mirror,  m,  is  carried  by  two  polygonal  forks,  F  f',  fixed,  one  to  the 
circle  of  declination,  the  other  to  the  circle  of  reflection.  In  p  the  ends  of  the 
forks  form  the  sides  of  a  movable  parallelogram,  of  which  the  changeable 
diagonal,  P  p',  rests  always  perpendicular  to  the  plane  of  the  mirror,  and 
divides  into  two  equal  parts  the  angle  of  the  two  forks.  In  the  middle  of  this 
arrangement  the  incident  and  reflected  rays  1  espectively,  parallel  to  the  stem 
of  the  forks,  make  equal  angles  with  the  normal  to  the  mirror ;  and  it  follows 
that  the  ray  which  falls  in  the  plane  of  the  circle  of  declination  is  constantly 
reflected  in  the  plane  of  the  circle  of  reflection. 

Mode  of  Using  the  Helios  tat. 

1.  When,  by  means  of  the  vernier  of  the  arc  of  latitudes,  the  angle  of  the 
latitude  in  degrees  and  minutes  is  indicated,  the  screw  ti  is  tightened 

2.  The  platform  is  made  horizontal  by  moving  round  the  disc,  and  by 
turning  gradually  the  screws  of  the  feet  which  regulate  the  spirit-level  in  two 
rectangular  positions,  so  that  in  each  of  the  positions  the  bubble  of  air  places 
itself  exactly  in  the  middle  of  the  spirit-level. 

The  level  of  the  instrument  is  perfect' when  its  centre  of  gravity  falls  on  that 
ray  or  claw  of  the  foot  which  carries  the  arresting  screw,  v,  of  the  disc. 

3.  The  declination  of  the  day  given  in  the  “  Nautical  Almanac”  in  degrees 
and  minutes  is  now  marked  by  the  vernier  of  the  circle  of  declination. 

4.  The  precise  hour  is  marked  by  the  hand  of  the  cubical  box,  B,  on  the 
dial  or  hour  circle,  C  C.' 

If  arranged  in  such  a  manner  that  the  solar  ray  passing  through  the  hole, 
p,  placed  at  the  extremity,  o',  of  the  circle  of  declination,  arises  so  as  to  fall  to 
the  centre  of  the  screen,  e,  fixed  on  the  same  circle,  the  operator  is  certain  that 
the  instrument  is  perfectly  set  towards  the  east,  as  regards  the  declination 
and  hour,  without  being  obliged  to  refer  to  a  chronometer  for  an  equation  of 
time.  The  centre  of  the  screen  is  indicated  by  the  crossing  of  the  two  wires 

5.  With  the  help  of  a  kev  which  fits  in  the  square  steel  let  into  the  cubical 
box,  B,  and  by  which  it  can  be  turned,  the  box  is  fixed  to  the  axis  of  the  clock, 
whose  movements  it  follows  whilst  carrying  the  circle  of  declination,  the 
mirror,  &c.  The  circle  of  reflection,  R  r',  is  raised  or  lowered  in  making  it 
turn  round  the  axis  of  the  heliostat  until  the  luminous  ray  falls  on  the  point 
to  be  illuminated.  By  tightening  the  screw  v'  and  the  screw  v",  placed  on 
the  cover  of  the  clock,  the  circle  of  reflection  and  mirror  are  fixed,  and  now 
the  heliostat  will  work  regularly. 

In  order  to  obtain  a  solar  spectrum  of  the  most  perfect  kind,  the  aperture 
through  which  the  light  passes  should  be  a  slit  not  more  than  the  twentieth 
part  of  an  inch  in  breadth,  and  the  length  rather  less  than  that  of  the  prism, 
placed  at  an  angle  of  sixty  degrees,  and  the  spectrum  thrown  on  the  white 
wall  or  screen,  which  should  be  from  sixteen  to  nineteen  feet  distant.  There 
is  a  lantern  containing  an  electric  lamp,  which  is  connected  with  a  power¬ 
ful  battery,  which  latter  may  be  placed  outside  the  lecture-room.  The  light 
is  condensed  by  a  plano-convex  lens,  and  passed  through  a  very  narrow 
slit  of  metal,  capable  of  adjustment  by  a  proper  motion,  so  that  it  can  be  made 
narrower  if  required.  The  slice  of  light,  or  thin  electric  light-ray,  is  now  per¬ 
mitted  to  fall  on  another  double-convex  lens,  which  causes  the  ray  to  converge 
a  little  more,  and  to  fall  upon  two  hollow  prisms  filled  with  bisulphide  of 
carbon,  which  enjoys  a  high  refractive  power.  After  passing  through  the  two 


no 


ON  LIGHT. 


prisms,  it  is  bent  on  to  the  screen  in  front ;  and  if  the  battery  is  in  good  order, 
the  most  vivid  colours  are  obtained. 

The  seven  colours  are  easily  caused  to  re-unite  and  form  white  light,  either 

by  passing  the  dispersed  rays  through 
a  fish-globe  full  of  water,  or  by  receiving 
them  on  to  a  double-convex  lens  (a,  Fig. 
97),  or  into  a  concave  mirror  (b,  Fig. 
97),  or  by  allowing  the  spectrum  formed 
by  one  prism  to  fall  on  another,  as  at  c, 
Fig.  97,  of  the  same  nature  and  at  the 
same  refracting  angle,  but  in  a  reversed 
position,  so  that  the  two  outer  faces  of 
the  two  prisms  become  parallel  to  each 
other,  and  in  fact  are  then  equivalent 
to  a  piece  of  flat  or  plane  glass. 

A  very  refined  and  beautiful  experi¬ 
ment,  originated  in  Paris  (Fig.  98),  is 
that  in  which  seven  mirrors  aTe  used, 
and  by  arranging  them  at  the  proper 
angles  they  may  be  made  to  reflect  each 
colour  separately  on  to  a  disc,  or  the 
whole  may  be  brought  together  to  pro¬ 
duce  one  spot  of  white  light. 

In  slating  that  light  is  made  up  of 
seven  colours,  it  must  be  borne  in  mind 


Fig.  98. — Apparatus  with  Seven  Plane 
Mirrors  for  reflecting  the  seven 
colours  of  the  Solar  Spectrum. 


that  they  are  not  considered  to  represent  the  ultimate,  but  proximate  analysis 
of  light.  One  of  Brewster’s  masterly  essays  is  that  in  which  he  endeavours  to 
prove  that  the  spectrum  is  entirely  pervaded  with  the  three  simple  colours, 
red,  yellow,  and  blue,  from  which  the  other  colours,  orange,  green,  indigo, 


*  Effected  in  three  ways — by  a  double-convex  lens,  a  j  a  concave  mirror,  b;  or  by  a  second  prism,  C. 


LIGHT  AND  COLOUR. 


1 1 1 


and  violet,  arise.  By  employing  the  absorptive  power  of  a  wedge  of  blue 
glass,  he  was  enabled  to  refute  the  conclusion  deduced  by  Newton,  “That  to 
the  same  degree  of  refrangibility  ever  belongs  the  same  colour,  and  to  the 
same  colour  ever  belongs  the  same  degree  of  refrangibility.”  Sir  Isaac  ex¬ 
amined  each  colour  separately  by  making  a  hole  in  the  screen  upon  which  the 
spectrum  fell  exactly  in  the  centre  of  each  colour,  and  allowing  that  colour  to 
fall  upon  another  prism ;  and  finding  that  this  second  refracting  surface  did 
not  change  or  decompose  the  special  colour  under  examination  into  any  other 
colours,  he  concluded  “  That  the  light  of  each  different  colour  had  the  same 
index  of  refraction;”  and  he  called  such  light  homogeneous  or  simple  light, 
whilst  ordinary  or  white  light  he  termed  heterogeneous  or  compound.  It  is 
this  enunciation  of  Newton  which  Brewster  disproved  by  the  following  experi¬ 
ments  He  says,  “  If  we  take  a  piece  of  blue  glass,  like  that  generally  used  for 
finger-glasses,  and  transmit  through  it  a  beam  of  white  light,  the  light  will  be 
a  fine  deep  blue.  This  blue  is  not  a  simple  homogeneous  colour  like  the  blue 
or  indigo  of  the  spectrum,  but  is  a  mixture  of  all  the  colours  of  white  light 
which  the  glass  has  not  absorbed,  and  the  colours  which  the  glass  has  absorbed 
are  those  which  the  blue  wants  of  white  light,  or  which,  when  mixed  with  this 
blue,  would  form  white  light.  In  order  to  determine  what  these  colours  are,  let 
us  transmit  through  the  blue  glass  the  prismatic  spectrum ;  or,  what  is  the 
same  thing,  let  the  observer  place  his  eye  behind  the  prism,  and  look  through 
it  at  the  sun,  or  rather  at  a  circular  aperture  made  in  the  window-shutter  of  a 
dark  room.  He  will  then  see  through  the  prism  the  spectrum  as  far  before 
the  aperture  as  it  would  be  above  the  spot  when  shown  on  the  screen.  Let  the 
blue  glass  be  now  interposed  between  the  eye  and  the  prism,  and  a  remarkable 
spectrum  will  be  seen,  deficient  in  a  certain  number  of  its  differently  coloured 
rays.  A  particular  thickness  absorbs  the  middle  of  the  red  space,  the  whole 
of  the  orange,  a  great  part  of  the  green,  a  considerable  part  of  the  blue,  a  little 
of  the  indigo,  and  very  little  of  the  violet.  The  yellow  space,  which  has  not 
been  much  absorbed,  has  increased  in  breadth.  It  occupies  part  of  the  space 
formerly  covered  by  the  orange  on  one  side,  and  part  of  the  space  formerly 
covered  by  the  green  on  the  other.  Hence 
it  follows  that  the  blue  glass  has  absorbed 
the  red  light  which,  when  mixed  with  the 
yellow  light,  constituted  orange,  and  has 
absorbed  also  the  blue  light  which,  when 
mixed  with  the  yellow,  constituted  the  part 
of  the  green  space  next  the  yellow.  We 
have  therefore,  by  absorption,  decomposed  M 
green  light  into  yellow  and  blue,  and  orange 
light  into  yellow  and  red;  and  it  conse  FlG.  99. 

quently  follows  that  the  orange  and  green 

rays  of  the  spectrum,  though  they  cannot  be  decomposed  by  prismatic  refrac¬ 
tion,  can  be  decomposed  by  absorption,  and  actually  consist  of  two  different 
colours  possessing  the  same  degree  of  refrangibility.  Difference  of  colour  rs, 
therefore ,  not  a  test  of  difference  of  refrangibility.  Red,  yellow,  and  blue 
light  exist  at  every  point  of  the  solar  spectrum.  1  he  existence  of  these 
primary  colours  in  the  spectrum,  and  the  mode  in  which  they  produce,  by 
their  combination,  the  seven  secondary  or  compound  colours  which  are  de¬ 
veloped  by  the  prism,  will  be  understood  from  !•  ig.  99,  where  M  N  is  the 
prismatic  spectrum,  consisting  of  three  primary  spectra  of  the  same  lengths, 


112 


ON  LIGHT. 


M  N,  viz.,  a  red,  a  yellow,  and  a  blue  spectrum.  The  red  spectrum  has  its 
maximum  intensity  at  R ;  and  this  intensity  may  be  represented  by  the  distance 
of  the  point  R  from  M  N.  The  intensity  declines  rapidly  to  M  and  slowly  to 
N,  at  both  of  which  points  it  vanishes.  The  yellow  spectrum  has  its  maximum 
intensity  at  Y,  the  intensity  declining  to  zero  at  M  and  N  ;  and  the  blue  has  its 
maximum  intensity  at  B,  declining  to  nothing  at  M  N.  The  general  curve  which 
represents  the  total  illumination  at  any  point  will  be  outside  these  three  curves, 
and  its  ordinate  at  any  point  will  be  equal  to  the  sum  of  the  three  ordinates 
at  the  same  point.  Thus  the  ordinate  of  the  general  curve  at  the  point  Y  will 
be  equal  to  the  ordinate  of  the  yellow  curve,  which  we  may  suppose  to  be  io, 
added  to  that  of  the  red  curve,  which  may  be  2,  and  that  of  the  blue,  which 


FiG.  100. — Herschel's  Direct- Vision  Prism. 

may  be  1.  Hence  the  general  ordinate  will  be  13.  Now,  if  we  suppose  that 
3  parts  of  yellow,  2  of  red,  and  1  of  blue  make  white,  we  shall  have  the  colour 
at  Y  equal  to  3  +  2-}- 1,  equal  to  6  parts  of  white  mixed  with  7  parts  of  yellow; 
that  is,  the  compound  tint  at  Y  will  be  a  bright  yellow,  without  any  trace  of 
red  or  blue.  As  these  colours  all  occupy  the  same  place  in  the  spectrum,  they 
cannot  be  separated  by  the  prism ;  and  if  we  could  find  a  coloured  glass  which 
would  absorb  7  parts  of  the  yellow,  we  should  obtain  at  the  point  Y  a  white 
light  which  the  prism  could  not  decompose.”  * 

It  may  be  useful  to  mention  that,  with  Herschel’s  direct-vision  prism,  filled 
with  bisulphide  of  carbon,  the  trouble  required  in  adjusting  the  lantern  so  as 
to  throw  the  spectrum  on  to  the  disc  is  obviated,  and  the  lantern,  with  its 
prism  attached,  may  be  placed  directly  in  front  of  the  screen,  as  in  any  other 
ordinary  optical  experiment.  • 


*  Het.nholtz  and  Airy  have  thrown  great  douotson  Brewster's  experiments  and  theory  of  the  spectrum. 


LIGHT  AND  COLOUR. 


113 


Physical  Properties  of  the  Spectrum. 

It  has  been  shown  how  a  ray  of  light  can  be  separated  into  its  proximate  or 
ultimate  colours.  These  various  portions  of  coloured  light  have  certain  distinct 
properties,  which  have  been  most  carefully  investigated  by  different  physicists. 
The  illuminating  power  of  the  spectrum,  as  might  be  imagined,  exists  in  the 
most  luminous  poYtion  of  the  band  of  colours,  viz.,  in  the  yellow  light;  and  experi¬ 
ments  carefully  conducted  by  Herschel  and  Frauenhofer  confirm  this  fact,  and 
show  that  the  greatest  amount  of  light  exists  nearer  the  red  than  the  violet 
end  of  the  spectrum.  The  calorific  power  of  the  spectrum  increases  gradually 
from  the  blue  colour ;  it  rises  to  its  maximum  in  the  red ;  but,  what  is  most 
curious,  it  reaches  its  greatest  elevation  beyond  the  limits  of  the  visible  red 
ray,  or  red  end  of  the  spectrum.  The  invisible  rays  of  heat  are,  therefore, 
more  powerful  than  the  other  heat-giving  rays  of  the  spectrum  accompanied 
with  light,  as  in  the  yellow,  orange,  or  red  colours ;  the  luminous  radiations  do 
not  give  so  much  heat  as  the  non-luminous  ones;  and  Tyndall,  speaking  of 
this  remarkable  circumstance,  says,  “In  the  region  of  dark  rays  beyond  the 
red  the  curve  shoots  up  in  a  steep  and  massive  peak,  a  kind  of  Matterhorn  of 
heat,  which  dwarfs  by  its  magnitude  the  portion  of  the  diagram  representing 
the  luminous  radiation.” 

The  chemical  influence  of  the  spectrum,  unlike  the  heating  and  illuminating 
rays,  is  at  its  minimum  at  the  red  end,  and  rises  gradually  in  intensity  towards 
the  violet.  Light  acts  as  a  chemical  agent  not  only  with  certain  portions  of 
its  luminous  rays,  but,  like  heat,  with  its  non-luminous  rays.  Ritter,  of  Jena, 
discovered  that  chloride  of  silver  was  acted  upon  and  blackened  beyond  the 
violet  end  of  the  spectrum.  Dr.  Herschel  and  Dr.  Wollaston  confirmed  this 
fact.  These  chemical  or  actinic  rays  have  been  carefully  studied  and  most 
industriously  employed,  so  that  a  new  art  has  been  created,  called  Photography, 
which,  in  a  thousand  different  ways,  is  now  made  subservient  to  the  require¬ 
ments  of  man.  Moser  has  discovered  that  certain  rays  have  the  power  to  set 
up  chemical  change,  and  this  once  begun  may  be  continued  with  other  co¬ 
loured  rays,  that  could  not  in  themselves  produce  chemical  decomposition.  An 
iodized  silver  plate,  with  an  engraving  placed  over  it,  was  exposed  to  light  until 
the  action  had  commenced  ;  if  this  plate  was  then  placed  under  a  violet  glass, 
the  picture  was  soon  obtained ;  whilst  a  long  time  elapsed,  and  the  result  was 
imperfect,  when  the  same  plate,  after  exposure  to  sunlight,  was  placed  under 
a  red  glass.  If,  however,  the  prepared  plate  was  first  exposed  in  a  camera  to  a 
blue  light,  and  then  placed  under  a  red  glass,  the  picture  was  speedily  obtained. 
In  the  early  portion  of  this  article  phosphorescence  has  been  considered,  and 
here  it  may  be  mentioned  that  Becquerel  calls  the  rays  capable  of  setting 
up  or  commencing  chemical  action  “exciting  rays,”  and  others  which  only 
possess  the  power  of  continuing  a  chemical  change  “  phosphoregenic  ”  or 
“continuing  rays,”  and  has  identified  the  latter  with  the  power  possessed  by 
light  of  rendering  certain  bodies  luminous.  (Seep.  9.)  It  is  the  phosphoregenic 
rays,  extending  from  the  indigo  to  beyond  the  violet  ray,  which  render  certain 
bodies  phosphorescent  by  insolation.  Becquerel  has  invented  a  most  ingenious 
instrument,  called  the  l’hosphoroscope,  by  which  substances  can  be  viewed 
directly  after  exposure  to  light,  and  the  time  of  the  duration  of  the  phos¬ 
phorescent  power  accurately  determined.  Thus  several  bodies,  which  are  only 
phosphorescent  for  some  fraction  of  a  second,  ha  /e  been  added  to  the  long 
list  of  substances  affected  in  a  similar  but  more  decided  manner. 

8 


ON  LIGHT 


114 


When  the  bright  rays  from  the  electric  lamp  are  passed  through  blue  glass, 
and  then  permitted  to  fall  upon  a  plate  of  glass  coloured  yellow  by  the  oxide 
of  uranium,  the  latter  becomes  self-luminous,  and  emits  rays  which  are  altered 
in  their  vibratory  power ;  the  original  rays  have  undergone  a  change  in  their 
refrangibility. 

To  these  phenomena,  which  Professor  Stokes  has  investigated  with  the 
greatest  care,  the  title  of  fluorescence,  or  internal  dispersion,  has'been  given. 
Figures  or  letters  painted  with  a  strong  solution  of  sulphate  of  quinine  in  tar¬ 
taric  acid  become  curiously  self-luminous  when  the  rays  passed  through  blue 
or,  better  still,  violet  glass  are  allowed  to  fall  upon  them.  A  little  sulphur 
burnt  in  a  jar  of  oxygen  emits  rays  which  render  paper  painted  with  an 
alcoholic  solution  of  stramonium  self-luminous. 

A  tube  of  uranium  glass,  conveying  the  coil-discharge  in  vacuo ,  is  similarly 
affected  by  this  peculiar  electric  light.  It  was  ascertained  that  prisms  made 
of  glass  appeared  to  absorb  a  larger  number  of  the  more  refrangible  rays, 
and  Professor  Stokes  found  that  by  using  prisms  made  of  quartz  he  could 
obtain,  with  the  electric  light,  a  spectrum  six  or  eight  times  as  long  as  the 
ordinary  one ;  and  his  experiments  indicate  that  the  chemical,  the  luminous,  the 
phosphorogenic  rays,  or  rays  of  high  refrangibility,  are  intimately  connected 
with  each  other,  and  are  only  so  many  effects  of  one  and  the  same  cause. 


The  Dark  or  Fixed  Lines  in  the  Solar  Spectrum. 

At  the  beginning  of  the  present  century,  in  the  year  1802,  Dr.  Wollaston 
announced  that  he  had  discovered  two  dark  lines,  one  in  the  green  and  the 
other  in  the  blue  space  of  the  solar  spectrum,  formed  by  a  prism  of  flint  glass. 
This  very  humble  beginning,  at  first  exciting  little  or  no  attention,  has  led  on 
to  a  series  of  most  valuable  experiments,  which  have  not  only  been  made  with 
terrestrial  substances,  but  have  even  by  analogy  conducted  the  aspiring  philo¬ 
sopher  to  the  far-distant  celestial  bodies,  where,  by  the  help  of  the  light 
emitted  and  reflected  from  them,  certain  conclusions  as  to  their  physical 
nature  and  aspect  have  been  arrived  at.  W ollaston  also  showed  his  great 
sagacity  as  an  observer,  in  discovering  the  bright  lines  in  the  spectrum  of  the 
electric  spark. 


Fig.  ioi. — Frauenh ofer’s  Seven  Lines  in  the  Solar  Spectrum. 


About  the  year  1814,  the  celebrated  mathematical  optician,  Frauenhofer,  of 
Munich,  repeated  Wollaston’s  experiment,  and  not  only  found  the  two  lines, 
but  discovered  that  the  spectrum  was  crossed  throughout  its  entire  length  by 
a  great  number  of  dark  lines  of  different  breadths.  In  consequence  of  the 
mdustry  with  which  Frauenhofer  continued  the  investigation,  and  the  care  with 
which  he  mapped  out  and  measured  the  exact  place  of  each  most  important 
line  in  the  spectrum,  they  have  by  universal  consent  been  called  FrauenhofeFs 


SPECTR  UM  ANAL  YSIS. 


1  r5 


lines;  of  these  seven  have  been  particularly  distinguished,  and  are  marked  B, 
C,  D,  E,  F.  G,  and  H,  Fig.  ioi. 

Thus  B  is  in  the  red  space,  near  the  end  ;  c  is  near  the  edge  of  the  red  ;  D 
is  in  the  orange,  and  is  a  strong  double  line,  separated  by  a  bright  one ;  E  is 
in  the  green,  consisting  of  several,  the  middle  one  being  the  strongest ;  F  is  in 
the  blue;  G  is  in  the  indigo;  and  H  in  the  violet.  These  special  lines,  so  care¬ 
fully  determined  by  Frauenhofer,  have  remained  as  fixed  points  of  reference. 
But  they  do  not  give  the  student  any  idea  of  the  immense  number  of  lines 
which  are  to  be  found  throughout  the  whole  length  of  the  visible  portion  of 
the  solar  spectrum,  and  even  in  the  invisible  rays  rendered  visible  by  the  experi¬ 
ments  of  Professor  Stokes.  Their  name  is  legion,  and  they  are  to  be  counted 
by  hundreds  and  thousands;  and  so  far  back  as  the  year  1814  Frauenhofer 
had  counted  600.  In  the  year  1830  Simms  constructed  the  first  most  import¬ 
ant  spectrum  apparatus.  In  1832  Brewster  carefully  examined  the  dark  lines 
produced  by  passing  the  spectrum  obtained  from  an  artificial  source  of  light 
through  nitrous  acid  gas;  at  first  he  thought  they  were  ider.tical  with  the  dark 
lines  in  the  solar  spectrum,  but  Professors  Daniell  and  Miller  proved  that 
this  was  not  the  case,  and  that  they  were  produced  by  the  absorptive  power 
of  the  gas.  In  the  year  1835  Wheatstone  observed  that  the  incandescent 
vapour  of  metals,  obtained  by  the  electric  discharge  through  metallic  poles, 
gave  certain  coloured  lines  peculiar  to  each  metal.  He  concluded  that  the 
electric  spark  results  from  the  volatilization  and  ignition,  not  the  combustion, 
of  the  ponderable  matter  of  the  poles  itself,  as  the  same  phenomena  were 
observed  in  hydrogen;  and  he  states  that  these  differences  of  spectra 
obtained  from  various  metallic  poles  “are  so  obvious,  that  one  metal  may 
instantly  be  distinguished  from  another  by  the  appearance  of  its  spark;  and 
we  have  here  a  mode  of  discriminating  metallic  bodies,  more  readily  appli¬ 
cable  even  than  a  chemical  examination,  which  may  hereafter  be  employed  for 
useful  purposes.”  How  true  this  prediction  proved  is  shown  in  the  construc¬ 
tion  and  use  of  the  apparatus  now  employed  to  obtain  the  spectra  of  terres¬ 
trial  metals  for  the  purpose  of  comparing  their  coloured  lines  with  the  black 
lines  obtained  from  the  light  of  the  sun,  the  fixed  stars,  &c.  The  apparatus 
made  by  Huggins  and  Miller,  and  applied  to  the  heavenly  bodies,  includes  a 
slit  for  the  admission  of  light,  and  over  one  half  of  it  is  placed  a  right-angled 
prism  to  receive  the  light  from  the  electric  sparks  obtained  from  metallic 
poles  and  sent  by  a  mirror  through  an  aperture  to  the  prism.  The  lines 
obtained  from  any  given  metal,  such  as  sodium,  could  be  at  once  compared  by 
exact  measurement  with  similar  black  lines  obtainable  from  solar  light,  and 
the  two  identified  with  each  other.  It  remained  for  Bunsen  and  Kirchoff, 
in  1859.  to  sum  up  all  the  labours  of  the  clever  men  who  had  preceded  them, 
and,  with  the  help  of  their  own  experiments,  to  read  Frauenhofer’s  black  lines 
as  if  they  were  hieroglyphics,  the  key  to  which  they  had  at  last  discovered  by 
elaborate  experiments.  Since  KirchofFs  discoveries,  Mr.  Huggins  and  Ur. 
Miller  have  steadily  persevered  in  the  same  path  of  spectrum  analysis,  and 
have  given  the  world  some  remarkable  facts,  showing  the  nature  of  the 
planets,  fixed  stars,  nebulae,  and  comets. 

The  chief  credit  has  fallen  to  Bunsen  and  Kirchoff,  because  they  skilfully 
grasped  the  whole  phenomena,  and  reduced  them  to  a  perfect  system  ;  it 
should,  however,  be  remarked  that,  as  far  back  as  the  year  1 7 5 Ihomas 
Melville  investigated  the  nature  of  coloured  flames,  and  specially  observed 
the  yellow  flame,  which  no  doubt  gave  Brewster  the  idea  of  the  monochro- 

8 — 2 


lit) 


ON  LIGHT. 


matic  lamp  and  light,  obtained  with  alcohol  and  salt.  In  1822  Sir  John 
Herschel  remarks  that,  “The  colours  thus  communicated  by  different  bases 
to  flame  affords  in  many  cases  a  ready  and  neat  way  of  detecting  extremely 
minute 'quantities  of  them.”  In  1834  Mr.  Fox  Talbot,  speaking  of  his  experi¬ 
ments  with  the  red  tint  of  flame  produced  by  lithium  and  strontium,  says, 
“  I  hesitate  not  to  say  that  optical  analysis  can  distinguish  the  minutest 
portion  of  these  substances  from  any  other,  with  as  much  certainty  as,  if  not 
more  than,  by  any  other  method.”  It  will  thus  be  seen  that  English  philo¬ 
sophers  were  not  wholly  ignorant  of  the  primary  truths  which  led  to  the  grand 
generalizations  of  Kirchoff.  Since  the  first  instrument  used  by  Bunsen  and 
Kirchoff,  other  and  more  perfect  instruments  have  been  made  for  spectrum 
analysis.  Probably  one  of  the  most  simple  in  construction  is  that  made  by 
Mr.  John  Browning,  with  the  assistance  of  Mr.  Herschel,  and  called  the 
Herschel-Browning  direct-vision  spectroscope,  in  which  the  direct  vision  is 
produced  by  a  combination  of  two  direct-vision  prisms.  It  is  shown  in 
Fig.  102. 


Fig.  1 02. —  T he  Herschel- Browning  Direct-  Vision  Spectroscope. 

A,  arrangement  of  the  two  prisms  B  b  bemg  direct- vision  prisms. 


For  quick  examination  of  atmospheric  lines,  and  for  noting  the  changes 
that  occur  near  the  horizon,  or  in  any  particular  direction,  this  form  of  the  spec¬ 
troscope  is  one  of  the  best  yet  devised,  as  it  can  be  instantaneously  and 
accurately  pointed  at  any  cloud  in  any  direction.  Its  dispersion  and  pre¬ 
cision  are  so  great  as  to  divide  Frauenhofer’s  line  D  with  a  magnifying  power 
of  only  5. 

Another  form  of  spectroscope,  which  is  exceedingly  useful  to  the  student, 
has  a  prism  of  extremely  dense  glass  of  superior  workmanship.  (Fig.  103  ) 
The  circle  is  divided,  and  reads  with  a  vernier,  thus  dispensing  with  the  incon¬ 
venience  of  an  illuminated  scale.  This  arrangement  possesses  the  very  great 
advantage  of  giving  angular  measures  in  place  of  a  perfectly  arbitrary  scale. 
The  slit  is  also  furnished  with  a  reflecting  prism,  by  means  of  which  two  spectra 
can  be  shown  in  the  field  of  view  at  once. 

For  elaborate  researches  a  larger  spectroscope  (Fig.  104),  containing  four 
dense  glass  prisms,  and  a  telescope  with  object-glasses  of  1^  in.  diameter  and 


SPECTRUM  ANALYSIS. 


ii7 


Fig.  103. 

.8  in.  focal  length,  may  be  employed.  A  powerful  train  of  eleven  prisms  was 
arranged  by  Mr.  Gassiot;  the  prisms  were  hollow,  and  filled  with  bisulphide 
of  carbon.  It  is  described  in  the  “  Phil.  Mag.”  [4]  xxviii.  69. 

Mr.  Browning  has  had  great  experience  in  the  construction  of  spectroscopes; 
he  made  the  Kew  Observatory  spectroscope,  furnished  with  nine  glass  prisms, 
another  of  eleven  fluid  prisms,  which  he  made  for  T.  P.  Gassiot,  Esq.,  and 
also  the  spectrum  apparatus  constructed  for  William  Huggins,  Esq.,  for  his 
important  researches  on  the  spectra  of  the  fixed  stars  ;  and  therefore  his  direc¬ 
tions  for  the  use  of  the  spectroscope  are  given  here. 

How  TO  USE  THE  SPECTROSCOPE. 

“  Screw  the  telescope  carrying  the  knife-edges  at  the  small  end  into  the 
upright  ring  fixed  on  to  the  divided  circle,  and  the  other  telescope  into  the 
ring  attached  to  the  movable  index.  Now  place  any  common  bright  light 
exactly  in  front  of  the  knife-edges,  and  while  looking  through  the  telescope 
on  the  movable  index  (having  first  unscrewed  the  clamping  screw  under  the 
circle),  turn  the  telescope  with  the  index  round  the  circle  until  a  bright  and 
continuous  spectrum  is  visible. 

TO  OBTAIN  THE  BRIGHT  LINES  IN  THE  SPECTRUM  GIVEN  BY  ANY 

SUBSTANCE. 

“  Remove  the  bright  flame  from  the  front  of  the  knife-edges,  and  substitute  in 
its  place  the  flame  of  a  common  spirit-lamp,  or,  still  better,  a  gas  jet  know  n  as 
a  Bunsen’s  burner  (Fig.  105).  Take  a  piece  of  platinum  wire,  about  the 
substance  of  a  fine  sewing  needle,  bend  the  end  into  a  small  loop  about  the 
eighth  of  an  inch  in  diameter ;  fuse  a  small  bead  of  the  substance  or  salt  to 
be  experimented  on,  into  the  loop  of  the  platinum  wire,  and,  attaching  it  to 
any  sort  of  light  stand  or  support,  bring  the  bead  into  the  front  edee  of  tire 


1 18 


ON  LIGHT. 


flame,  a  little  below  the  level  of  the  knife-edges.  If  the  flame  be  opposite  the 
knife-edges  on  looking  through  the  eye-piece  of  the  telescope,  the  fixed  lines 
due  to  the  substance  will  be  plainly  visible.  When  minute  quantities  have  to 
be  examined,  the  substance  should  be  dissolved,  and  a  drop  of  the  solution, 
instead  of  a  solid  bead,  be  used  on  the  platinum  wire. 


SPECTRUM  ANALYSIS. 


no 


“The  delicacy  of  this  method  of  analysis  is  very  great.  Swan  found,  in 
1657  (Ed.  Phil.  Trans.,  vol.  xxi.,  p.  41 1),  that  the  lines  of  sodium  are  visible 
when  a  quantity  of  solution  is  employed  which  does  not  contain  more  than 
1-2, 500,000th  of  a  grain  of  sodium. 

“To  view  Frauenhofer’s  lines  on  the  solar  spectrum,  it  is  only  necessary  to 
turn  the  knife-edges  towards  a  white  cloud,  and  make  the  slit  formed  by  the 
knife-edges  very  narrow,  by  turning  the  screw  at  the  side  of  them.  In  every 
instance  the  focus  of  the  telescope  must  be  adjusted  in  the  ordinary  way,  by 
sliding  the  draw-tube  until  it  suits  the  observer’s  sight,  and  distinct  vision  is 
obtained. 


Fig.  105. — A  Bunsen  Burner ,  with  Ring-stand ,  supporting  the  Platinum 

Wire 

“  It  should  be  noted  that  lines  at  various  parts  of  the  spectrum  require  a 
different  adjustment  in  focusing  the  telescope. 

“  The  small  prism  turning  on  a  joint  in  front  of  the  knife-edg;es  is  for  the 
purpose  of  showing  two  spectra  in  the  field  of  view  at  the  same  time.  To  do 
this  it  must  be  brought  close  to  the  front  of  the  knife-edges.  1  hen  one  flame 
must  be  placed  in  the  position  in  which  the  flame  of  the  candle  is  shown  in 
the  small  figure,  and  the  other  directly  in  front  of  the  slit.  On  looking 
through  the  telescope  as  before  described,  the  spectra  due  to  the  two  sub¬ 
stances  will  be  seen  one  above  the  other. 

“  When  the  slit  is  turned  towards  a  bright  cloud,  and  a  light  is  used  in  the 
position  of  the  candle  flame,  the  spectrum  of  any  substance  may  be  seen, 
compared  with  the  solar  spectrum.  In  this  manner  Kirchoff  determined  in 
the  solar  spectrum  the  presence  of  the  lines  of  the  greater  number  of  the 
elements  which  are  believed  to  exist  in  the  sun. 

PROFESSOR  STOKES’S  ABSORPTION  BANDS. 

“  The  instrument  is  expressly  adapted  to  the  prismatic  analysis  of  organic 
bodies,  according  to  the  method  recommended  by  Professor  Stokes,  in  his 
lecture  at  the  Chemical  Society,  printed  in  the  ‘  Chemical  News.’ 

“To  observe  these  bands  it  is  only  necessary  to  place  a  very  dilute  solu- 


120 


ON  LIGHT. 


tion  of  the  substance  in  a  test-tube,  then  fix  the  test-tube  in  the  small  clip 
attached  to  a  ring,  which  slips  on  in  front  of  the  knife-edges.  Upon  bringing 
any  bright  light  in  front  of  the  tube,  on  looking  through  the  telescope,  if  the 
instrument  has  been  pioperly  adjusted,  a  bright  spectrum  will  be  seen,  inter¬ 
rupted  by  the  dark  bands  due  to  the  substance  in  solution. 

“  One  of  the  simplest  and  most  interesting  experiments  of  this  kind  can  be 
made  by  preparing  dilute  solutions  of  madder,  port  wine,  and  blood. 

“  In  these  very  dilute  solutions  no  difference  can  be  detected  by  the  unas¬ 
sisted  eye ;  but  on  submitting  them,  in  the  manner  already  described,  to  the 
test  of  spectrum  analysis,  very  different  appearances  will  be  presented. 

“  The  absorption  bands  may,  however,  be  most  conveniently  examined, 
and  accurately  investigated,  by  means  of  Sorby  and  Browning’s  new  Micro- 
spectroscope.” 

As  will  be  seen  from  Fig.  106,  it  is  a  very  compact  piece  of  apparatus,  very 
ingenious  in  construction,  and  consisting  of  several  parts.  The  prism  is  con¬ 
tained  in  a  small  tube,  which  can  be  removed  at  pleasure.  Below  the  prism 
is  an  achromatic  eye-piece,  having  an  adjustible  slit  between  the  two  lenses; 
the  upper  lens  being  furnished  with  a  screw  motion  to  focus  the  slit.  A  side 


Fig.  106. 


SPECTRUM  ANALYSIS. 


1 2  I 


slit,  capable  of  adjustment,  admits,  when  required,  a  second  oeam  of  light 
from  any  object  whose  spectrum  it  is  desired  to  compare  with  that  of  the 
object  placed  on  the  stage  of  the  microscope.  This  second  beam  of  light 
strikes  against  a  very  small  prism  suitably  placed  inside  the  apparatus,  and 
is  reflected  up  through  the  compound  prism,  forming  a  spectrum  in  the  same 
field  with  that  obtained  from  the  object  on  the  stage 

A  is  a  brass  tube  carrying  the  compound  direct-vision  prism. 

R  is  a  milled  head,  with  screw  motion  to  adjust  the  focus  of  the  achromatic 
eye-lens. 

C,  milled  head,  with  screw  motion  to  open  or  shut  tlfe  slit  vertically.  Another 
screw  at  right  angles  to  C,  and  which,  from  its  position,  could  not  be  shown  in 
the  cut,  regulates  the  slit  horizontally.  This  screw  has  a  larger  head,  and  when 
once  recognized  cannot  be  mistaken  for  the  other. 

D  D,  an  apparatus  for  holding  small  tube,  that  the  spectrum  given  by  its 
contents  may  be  compared  with  that  from  any  other  object  on  the  stage. 

E,  square-headed  screw,  opening  and  shutting  a  slit  to  admit  the  quantity 
of  light  required  to  form  the  second  spectrum.  Light,  entering  the  round 
hole  near  E,  strikes  against  the  right-angled  prism  which  we  have  mentioned 
as  being  placed  inside  the  apparatus,  and  is  reflected  up  through  the  slit 
belonging  to  the  compound  prism.  If  any  incandescent  object  is  placed  in  a 
suitable  position  with  reference  to  the  round  hole,  its  spectrum  will  be  obtained, 
and  will  be  seen  on  looking  through  it. 

F  shows  the  position  of  the  field  lens  of  the  eye-piece. 

G  is  a  tube  made  to  fit  the  microscope  to  which  the  instrument  is  applied. 
To  use  this  instrument,  insert  G,  like  an  eye-piece  is  in  the  microscope-tube, 
taking  care  that  the  slit  at  the  top  of  the  eye-piece  is  in  the  same  direction  as 
the  slit  below  the  prism.  Screw  on  to  the  microscope  the  object-glass  required, 
and  place  the  object  whose  spectrum  is  to  be  viewed  on  the  stage.  Illuminate 
with  stage  mirror  if  transparent,  with  mirror  and  Lieberkuhn  and  dark  well  if 
opaque,  or  by  side  reflector,  bull’s-eye,  & c.  Remove  A,  and  open  the  slit  by 
means  of  the  milled  head,  not  shown  in  cut,  but  which  is  at  right  angles  to 
I)  D.  When  the  slit  is  sufficiently  open,  the  rest  of  the  apparatus  acts  like  an 
ordinary  eye-piece,  and  any  object  can  be  focused  in  the  usual  way.  Having 
focused  the  object,  replace  A,  and  gradually  close  the  slit  till  a  good  spectrum 
is  obtained.  The  spectrum  will  be  much  improved  by  throwing  the  object  a 
little  out  of  focus. 

Every  part  of  the  spectrum  differs  a  little  from  adjacent  parts  in  refrangi- 
bility,  and  delicate  bands  or  lines  can  only  be  brought  out  by  accurately 
focusing  their  own  parts  of  the  spectrum.  1  his  can  be  done  by  the  milled 
head  B.  Disappointment  will  occur  in  any  attempt  at  delicate  investigation, 
if  this  direction  is  not  carefully  attended  to. 

When  the  spectra  of  very  small  objects  are  to  be  viewed,  powers  of  fiom 
£  in.  to  i-2oth,  or  higher,  may  be  employed.  . 

Blood,  matter,  aniline  red,  permanganatc-of-potash  solution  (quite  fresh), 
are  convenient  substances  to  begin  experiments  with.  Solutions  that  are  too 
strong  are  apt  to  give  dark  clouds  instead  of  delicate  absorption  bands. 

Mr.  Browning  makes  small  cells  and  other  contrivances  to  hold  fluids  foi 

examination.  .  ,. 

The  spectra  obtainable  from  solid,  liquid,  and  gaseous  incandescent  bodies 

may  be  arranged  in  three  orders. 

A  spectrum  of  the  first  order  is  that  which  is  produced  by  a  solid  mean- 


122 


ON  LIGHT. 


Fig.  107. 

Arrangement  of  Charcoal 
Crucible  a.  containing 
sliver.  Contact  is  made 
with  the  charcoal  pole 
B,  and  the  metal  vapour¬ 
ized. 


descent  substance,  such  as  charcoal.  The  band  of  colours  is  continuous  from 
red  to  violet,  and  therefore  can  teach  little  or  nothing  of  the  constitution  of 
the  body  producing  the  light ;  such  a  spectrum  could 
not  be  employed  for  analytical  purposes.  A  spectrum  of 
the  second  order  differs  essentially  from  the  first,  inas¬ 
much  as  the  colours  are  not  continuous,  but  consist  of 
distinct  coloured  bands ;  it  can  only  be  obtained  from 
light  emitted  from  incandescent  gases  ;  and  any  sub¬ 
stance  which  can  be  converted  into  a  gaseous  state  by 
intense  heat  without  undergoing  decomposition  will  afford 
distinct  bands  of  colour,  which  are  always  the  same. 
The  metal  silver  placed  in  a  cup-shapcd  charcoal  pole 
and  connected  with  the  other  pole,  in  the  electric  lantern 
figured  in  the  frontispiece,  is  converted  into  silver  gas, 
and  produces  on  the  disc  two  distinct  green  lines.  (See 
Frontispiece.) 

Thallium — so  cleverly  discovered  by  Mr.  Crookes,  in 
1861,  in  certain  kinds  of  iron  pyrites,  and  so  called  from 
the  Greek  because  it  produces  a  splendid  green  flame— 
would  probably  have  been  unknown  but  for  this  new 
method  of  analysis.  The  attention  of  Mr.  Crookes  was 
first  directed  to  the  splendid  green  line  as  obtained  from 
certain  specimens  of  pyrites,  and  it  was  by  following  up 
this  simple  fact — this  slender  clue — that  he  was  at  last 
enabled  to  isolate  the  body  that  produces  the  green  lines, 
and  confidently  pronounce  it  to  be  a  metal.  Spectra  of  various  metals  are 
shown  in  the  frontispiece.  In  projecting  metal  spectra  on  to  the  disc,  it  must 
be  understood  that  for  exact  purposes  of  research  they  cannot  be  so  truthful 
as  the  spectra  results  obtained  by  the  instruments  described  on  p.  95.  The 
optical  arrangements  required  to  show  the  spectra  of  incandescent  metals  to 
a  large  audience  on  the  disc  cannot  be  compared  to  the  elaborate  instruments 
already  mentioned.  Moreover,  the  charcoal  crucible  and  points  contain  ash 
consisting  of  alkaline  earths  and  salts,  which  must  interfere  with  the  spectrum, 
results.  A  spectrum  of  the  third  order  is  obtained  when  the  regularity  of  the 
spectrum  is  interfered  with  by  black  fixed  lines.  Such  a  spectrum  is  always 
obtained  from  the  rays  of  the  sun.  As  Mr.  Huggins  remarks,  “These  dark 
spaces  are  not  produced  by  the  source  of  light.”  They  tell  us  of  vapours 
through  which  the  light  has  passed  on  its  way,  and  which  have  robbed  the 
light  by  absorption  of  certain  definite  colours  or  rates  of  vibration.  A  very 
simple  mode  of  showing  such  a  spectrum  crossed  by  dark  lines  is  to  interpose 
between  the  slit  of  the  electric  lantern  and  the  double-convex  lens  a  vessel 
containing  some  nitrous  acid  gas.  Directly  this  is  done,  all  the  visible  indigo, 
blue,  and  green  colours  vanish,  and  the  remainder  of  the  spectrum  is  crossed 
with  numerous  dark  lines.  In  using  the  electric  lantern  it  must  always  be 
borne  in  mind  that  if  the  aperture  or  slit  is  too  widely  opened  the  dark  lines 
are  very  indistinct.  The  slit  should  be  very  narrow  indeed  to  display  the 
dark  lines  sharp  and  distinct.  A  more  instructive  mode  is  first  to  produce 
the  two  yellow  lines  representing  the  spectrum  of  sodium,  and  then  with  a 
peculiar-shaped  crucible  (Fig.  108). 

It  was  by  this  and  kindred  experiments  that  Kirchoff  showed  that  if  vapours 
of  terrestrial  substances  come  between  the  eye  and  an  incandescent  body, 


SPECTRUM  ANALYSIS. 


123 


they  cause  groups  of  dark  lines,  and,  further,  that  the 
group  of  dark  lines  produced  by  each  vapour  is  iden¬ 
tical  in  the  number  of  lines  and  in  their  position  in 
the  spectrum  with  the  group  of  lines  of  which  the  light 
of  the  vapour  consists  when  it  is  luminous. 

The  reversal  of  the  spectrum  of  coloured  flame, 
and  the  mode  in  which  he  obtained  the  proof  of  the 
identity  between  the  terrestrial  sodium  line  and  the 
dark  lines  similarily  placed  -in  the  solar  spectrum,  is 
thus  described  by  Kirchoff  : 

“  In  order  to  test  by  direct  experiment  the  truth  of 
the  frequently  asserted  fact  of  the  coincidence  of  the 
sodium  lines  with  the  lines  I)  (Frauenhofer),  I  obtained 
a  tolerably  bright  solar  spectrum,  and  brought  a  flame 
coloured  by  sodium  vapour  in  front  of  the  slit.  I  then 
saw  the  dark  lines  D  change  into  bright  ones.  The 
flame  of  a  Bunsen’s  lamp  threw  the  bright  sodium 
lines  upon  the  solar  spectrum.  In  order  to  find  out 
the  extent  to  which  the  intensity  of  the  solar  spectrum 
could  be  increased  without  impairing  the  distinctness 
of  the  sodium  lines,  I  allowed  the  full  sunlight  to  shine 
through  the  sodium  flame  upon  the  slit,  and,  to  my 
astonishment,  I  saw  that  the  dark  lines  D  appeared 
with  an  extraordinary  degree  of  clearness.” 

With  respect  to  this  important  experiment,  showing  the  reversal  of  the 
sodium  lines,  perhaps  the  most  simple  experiment  is  that  of  Roscoe,  who 
seals  up  some  of  the  metal  sodium  in  a  vacuum  tube,  and  on  volatilizing  the 
metal  the  vapour  is  colourless  by  white  light,  but  dark  and  opaque  when  the 
monochromatic  or  yellow  light  of  sodium  is  shown  behind  it. 

It  was  by  the  exact  reversal  of  the  bright  terrestrial  lines,  and  the  absolute 
identity  in  position  of  the  bright  terrestrial  and  dark  solar  lines,  that  Kirchoff 
discovered  the  elements  that  exist  in  the  sun,  viz.,  hydrogen,  sodium,  magne¬ 
sium,  iron,  calcium,  nickel,  chromium,  copper,  zinc,  barium,  and  probably 
strontium,  cobalt,  cadmium. 

At  p.  92,  and  in  Fig.  101,  are  shown  the  lines  B,  C,  n,  E,  F,  G,  and  H,  which 
are  called  Frauenhofer’s  principal  fixed  dark  lines  in  the  solar  spectrum.  The 
labours  of  Kirchoff  have  now  almost  interpreted  the  whole  of  these  lines, 
which  are  read  as  follows  : 


Fig.  108. 

The  section  of  the  Crucible  to 
be  used  for  showing  the  re¬ 
versal  of  the  bright  sodiurr 
lines,  of  which  a  is  the  cen¬ 
tral  hole,  and  contains  some 
chloride  of  sodium,  and  B  B 
a  ring  or  trench  all  round  A, 
in  which  metallic  sodium  is 
placed ;  c,  the  upper  char¬ 
coal  pole. 


C,  F,  and  G  are  Hydrogen. 
D  is  Sodium. 

E  is  Iron. 


H,  Aluminium. 
C,  Magnesium. 


The  limits  of  this  work  do  not  permit  the  consideration  of  stellar  che¬ 
mistry,  and  the  extremely  valuable  researches  of  Mr.  Huggins  and  Dr.  Miller 
in  this  direction;  but  the  reader  is  referred  to  Mr.  Huggins’s  discourse  “On 
the  Results  of  Spectrum  Analysis  applied  to  the  Heavenly  Bodies,”  published 
by  Ladd  ;  or  to  Mr.  Watt’s  “  Dictionary  of  Chemistry,”  for  a  complete 
resume  of  this  subject.  This  much  may  be  said,  that  spectrum  analysis 
proves  that  the  fixed  stars  are  suns  like  our  own — a  fact  which  could  only  be 
assumed  and  taken  for  granted  before  the  important  experiments  of  Kirchoff, 
Huggins,  and  Miller. 


124 


ON  LIGHT. 


Fig.  109. — Star  Spectroscope ,  with  adjustible  Reflecting  Prism  and  Mirror. 

With  finest  object-glass  micrometric  apparatus  lor  measuring  the  lines  of  the  spectrum  to  1-10, oooth  of 
an  inch,  extra  eye-piece,  and  ivory  tube  to  reader  of  vernier,  as  made  for  W.  Huggins,  Esq  ,  F.R.S  , 
and  used  during  the  observation  of  the  red  dames  of  the  sun  in  India,  August.  1868. 


Moreover,  the  spectroscope  has  discovered  the  real  nature  of  the  “red 
flames”  or  “  prominences”  of  the  sun,  which  are  invisible  under  ordinary  cir¬ 
cumstances,  being  overpowered  by  the  dazzling  brilliancy  of  the  rays  which 
proceed  from  the  sun  ;  but  visible  during  the  few  minutes  that  elapse  during  a 
total  eclipse  of  the  sun,  as  in  the  one  which  created  so  much  interest  in  August 
of  the  present  year,  1868,  visible  only  in  the  line  or  path  of  the  shadow,  which 
fell  in  India.  Four  xpeditions  went  to  India  to  observe  the  red  flames;  they 
were  all  armed  with  the  spectroscopic  apparatus,  and  their  united  statements 
all  agree  that  the  red  flames  belong  to  the  sun,  and  that,  as  they  give  bright  lines 
which  belong  only  to  spectra  of  the  second  order,  they  must  be  enormous 
heaps,  intensely  ignited  or  self-luminous.  The  bright  lines  chiefly  observed  appear 
to  be  those  which  belong  to  hydrogen  gas  and  sodium,  at  least  so  far  as  we  know 
at  present  (September,  1868);  and  this  interesting  statement  was  made  through 
the  telegrams  from  Major  Tennant,  Lieutenant  Herschel,  and  M.  Jannsen, 
which  arrived  in  England,  and  were  all  sent  independently  of  each  other.  As 
the  red  flames  belong  to  the  sun  and  show  bright  lines  in  the  spectroscope, 
are  they. great  volumes  of  the  photosphere  thrust  out  (like  the  pips  and  juice 
of  a  squeezed  gooseberry)  beyond  the  last  or  gaseous  atmosphere,  which 
usually  robs  the  light  from  the  photosphere  of  its  beautiful  coloured  bands, 


LIGHT  AND  COLOUR. 


1 25 


and  changes  them  to  dark  lines  ?  for  where  light  is  not,  there  can  only  be 

darkness. 

These  and  other  facts  are  discoverable  by  another  modification  of  the  spec¬ 
troscopic  arrangement  (Fig.  109),  as  constructed  by  Mr.  Browning. 

Spherical  Aberration. 

In  using  an  ordinary  concave  mirror  the  experimentalist  cannot  fail  to 
notice  that  the  rays  reflected  from  the  part  near  the  circumference  do  not 
come  to  the  same  meeting-point  or  focus  as  the  rays  reflected  from  parts  near 
the  centre.  (Fig.  1 10.)  It  is  evident  that  the  rays  A  B,  A  c,  come  to  a  focus  at 
G,  which  is  further  off  than  the  focus  F  from  the  parallel  rays  d  d,  d  d.  The 
distance  between  F  and  G,  the  two  foci,  is  called  the  longitudinal  spherical 


Fig.  1 10. — Concave  Mirror ,  showing  the  Aberration  of  the  Rays  of  Light. 

aberration.  The  natural  consequence  must  be  that  an  image  projected  by 
an  ordinary  concave  mirror  will  be  confused,  because  the  eye  has  to  look  at  a 
double  image,  the  one  superposed  on  the  other.  To  get  rid  of  the  rays  from 
the  outer  part  of  the  mirror  it  is  usual  to  employ  a  screen,  so  that  the  rays 
D  D,  D  D,  from  the  central  part  of  the  mirror  only  are  used. 


Fig.  iii. — Production  of  Caustic  Curves.  Fig.  112. 


Arising  from  this  circumstance  is  the  unequal  illumination  of  a  white 
ground  on  which  rays  are  reflected  to  different  foci,  and  the  production  of 
symmetrical  curves,  termed  caustic  lines  or  caustic  curves,  in  the  study  of 
which  mathematicians  have  been  most  industrious.  Brewster  lays  claim  to 
the  following  method  of  exhibiting  caustic  curves.  He  recommends  the  use 


126 


ON  LIGHT. 


of  a  piece  of  steel  spring  highly  polished,  or,  better  still,  polished  silver,  which 
is  to  be  bent  into  a  concave  figure  and  placed  vertically  on  its  edge  upon  a 
piece  of  card  or  white  paper,  and  when  exposed  either  to  the  rays  of  the  sun 
or  any  good  artificial  light,  the  curves  shown  in  Fig.  1 1 1  are  well  defined. 

In  the  same  way,  passing  from  reflecting  to  refracting  bodies,  the  spherical 
figure  of  a  convex  lens  causes  the  rays  which  fall  near  the  outer  edge  to  come 
to  a  focus  nearer  the  lens  than  the  rays  which  are  refracted  from  the  centre. 

The  result,  as  might  be  expected,  is  just  the  reverse  of  the  concave  mirror. 
The  rays  ag,ab,  Fig.  1 12,  falling  on  the  margin  of  the  double-convex  lens  are 
refracted  to  a  focus  at  F,  whilst  those  rays,  D  D,  D  D,  which  fall  near  the  axis  of 
the  lens  come  together  at  a  more  remote  point,  viz.,  at  C.  Here  again  a 
screen  or  diaphragm  cutting  off  the  rays  refracted  from  the  outer  edge  of  the 
lens  gives  a  better  image  ;  the  picture  produced  by  such  a  lens,  provided  with 
a  screen,  can  be  focused  more  distinctly ;  hence  telescopes,  microscopes, 
cameras,  oxy-hydrogen  lanterns,  &c.,  &c.,  are  usually  fitted  with  diaphragms, 
which  reduce  the  light,  but  cause  the  images  to  become  more  distinct.  The 
lens  of  the  eye  would,  from  this  cause,  project  on  to  the  retina  a  confused  or 
double  picture,  which  might  render  vision  extremely  imperfect  ;  this,  however, 
is  prevented  by  the  iris,  which  acts  as  a  diaphragm,  thus  the  aberration  of 
sphericity  is  corrected. 

The  Dispersion  of  Light,  or  Chromatic  Aberration. 

If  light  consisted  of  a  series  of  coloured  rays,  everyone  of  which  possessed 
the  same  index  of  refraction  when  they  fall  upon  a  glass  lens,  they  would  all 
come  together  in  the  same  spot,  and  white  light  only  would  be  obtained  ;  but 
this  is  not  the  case,  and  it  is  known  in  practice  that  lenses,  and  especially  con¬ 
densing  lenses,  project  coloured  rings,  and  give  images  with  coloured  edges. 
And  this  is  not  remarkable  when  it  is  remembered  that  a  double-convex  lens 
may  be  regarded  as  a  series  of  prisms  united  at  their  bases,  and  therefore 
capable  of  decomposing  or  dispersing  light.  It  is  a  singular  fact  that  Sir 
Isaac  Newton  considered,  from  the  experiments  he  had  tried  with  various 
prisms,  that  dispersion  was  proportioned  to  refraction,  and  he  believed  that 
all  substances  had  the  same  chromatic  aberrations  when  formed  into  lenses, 
and  that  any  combination  of  a  concave  with  a  convex  glass  would  produce 
colour  with  refraction.  Newton  reasoned  only  from  the  facts  he  had  acquired 
on  the  dispersive  powers  of  bodies,  and  pronounced  the  construction  of 
achromatic  telescopes  which  should  not  project  images  with  coloured  edges 
to  be  impossible.  The  fallibility  even  of  his  great  mind  is  shown  by  the  fact 
that,  a  few  years  after  his  death,  Hall  in  1733,  and  Dollond,  the  famous 
optician,  in  1757,  demonstrated  that  by  using  two  media,  viz.,  crown  and 
flint  glass,  of  different  refractive  and  dispersive  powers,  a  lens  may  be  formed 
which  is  achromatic. 

The  principle  of  the  achromatic  lens  is  not  complicated  or  difficult  to 
understand,  provided  the  previous  matter  relating  to  compound  and  simple 
colours  (p.  89)  has  been  already  studied.  Given  a  lens  made  of  a  certain  glass, 
and  projecting,  amongst  other  colours,  a  ring  of  red  light,  what  colour,  pro¬ 
jected  from  another  lens,  is  required  to  neutralize  it  ?  The  answer  is  obvious  : 
any  colour  which  together  with  the  red  light  would  form  white  light.  That  colour 
must  be  green,  because  it  contains  yellow  and  blue  ;  and,  as  already  shown, 
red,  yellow,  and  blue  form  white  light.  In  the  adjustment  of  the  two  lenses 


LIGHT  AND  COLOUR. 


12  7 


forming  the  achromatic  (Fig.  1 1 3),  it  is  so  arranged  that  the  colours  which  would 
be  separately  produced  by  each  lens  shall,  when  combined,  by  their  unequal 
dispersion  fall  together  at  the  same  spot  and  unite  together.  Any  two  colours 
which  unite  and  form  white  light  are  said  to  be  complementary,  and  there  is 
a  very  conclusive  experiment  which  may  be  performed  with  polarized  light 
passed  through  a  selenite  slide  placed  behind  a  Nicol’s  prism  composed  of 


Fig.  1 1 3. 

No.  1  .  Dollonil’s  Achromatic  Lens,  consisting  of  one 
double-convex  crown  glass  lens,  a,  anil  another 
concavo-convex  lens  of  (lint  glass,  t>;  No.  11.,  Dr. 
Blair’s  Achromatic  Lens,  composed  of  two  double- 
convex  ltnses  of  crown  glass,  enclosing  a  solution 
of  chloride  of  antimony. 


Fig.  114. —  Complementary  Colours 
overlapping  and  forming  White 
Light. 


double-refracting  spar.  The  two  discs  of  light  projected  on  to  the  screen 
separately  are  green  and  red ;  but  when  caused  to  overlap  each  other  by 
enlarging  the  aperture  through  which  they  pass,  the  two  colours  unite  in  the 
centre,  forming  white  light,  whilst  red  and  green  remain  intact  in  those  po¬ 
sitions  which  do  not  overlap.  (Fig.  114.) 

Other  complementary  colours  would  be  yellow  and  indigo,  blue  and  orange. 

0 

A 

X 


% 

Fig.  1 15. — Arrangement  of  the  Lenses  in  a  Refracting  Telescope . 

a  B,  Huygenian  eye-piece  ;  c  d,  erecting-glasses  ;  e,  stop  with  small  hole  to  cut  off  aberrant  rays  ; 

o,  object-glass. 

Flint  glass  has  a  greater  dispersive  power  than  crown  glass  ;  it  will  spread  or 
disperse  the  spectrum  over  a  larger  space.  I  he  dispersive  power  of  the  prism 
used  in  decomposing  light  for  showing  the  spectra  of  incandescent  metal  is 
increased  by  tilling  them  with  carbonic  disulphide  (bisulphide  of  carbon),, 
and  the  composition  and  dispersive  powers  of  the  three  bodies  is  as  follows  : 

Crown  glass . 0  039 

Flint  glass  ......  0  048 

Carbonic  disulphide  .  .  .  •  0115 


128 


ON  LIGHT. 


THE  INTERFERENCE  OF  LIGHT. 

Colours  of  Thin  Plates. 

About  the  year  1672,  Dr.  Hook,  a  very  clever  mechanician,  and  learned  in  all 
the  science  of  his  day,  discovered  that  by  splitting  mica,  which  is  free  from 
colour,  and  sometimes  used  instead  of  glass,  into  very  thin  films,  they 
exhibited  the  most  beautiful  colours.  But  as  they  were  less  than  the  twelve- 
thousandth  part  of  an  inch  in  thickness,  Dr.  Hook  could  not  measure  them, 
and  was  therefore  unable  to  determine  the  law  that  regulated  the  production 
of  any  particular  colour,  according  to  the  thickness  of  the  film  of  mica.  In 
due  course  of  time  the  experiments  engaged  the  attention  of  Sir  Isaac  Newton, 
and  directly  he  touched  the  subject  it  was  truly,  so  far  as  intellect  was  con¬ 
cerned,  with  the  hand  of  a  giant,  and  he  soon  discovered  a  method  of  measur¬ 
ing  the  films.  He  did  not  begin  with  mica,  because  it  would  have  been  very 
troublesome,  if  not  impossible,  to  split  it  into  a  graduated  series  of  films  of  the 
extreme  thinness  required  to  produce  colour.  Newton  therefore  commenced 
with  air,  and  having  once  determined  the  law,  it  was  easy,  knowing  the  index 
of  refraction  of  all  other  transparent  bodies,  to  work  out  by  calculation  the 
respective  thicknesses  required  to  produce  the  same  colours.  He  took  a  plano¬ 
convex  lens,  the  radius  of  whose  convexity  was  14  ft.,  and  placed  it  on  a 
double-convex  lens,  the  radius  of  whose  convexity  was  50ft.,  and  by  means  of 
proper  clamps  and  screws  the  surfaces  of  the  two  lenses  could  be  brought 
closely  together.  The  convexity  of  the  lower  lens  being  so  extremely  slight, 
it  might  indeed  be  almost  regarded  as  a  flat  surface,  like  any  moderate  area 
on  the  surface  of  the  globe,  because  the  sphere  of  glass  (of  which  the  lens 
would  be  a  slice)  had  a  theoretical  diameter  of  100  ft.  (Fig.  116.) 


Fig.  i  1 6. — Instrument  used  by  Newton  to  obtain  the  Rings  of  Colour  from 

Thin  Plates  of  Air. 

l  l,  upper  lens  pressed  on  the  lower  one,  l  l,  by  the  thumb-screws  />/>/>. 

When  the  two  lenses  were  pressed  together,  concentric  rays  of  colour  maae 
their  appearance ;  indeed  the  same  kind  of  effect  is  often  produced  acci¬ 
dentally  when  a  number  of  flat  plates  of  window-glass  are  piled  one  above 
the  other,  the  enclosed  air  being  then  pressed  by  the  weight  of  the  superin¬ 
cumbent  glass  into  a  film  sufficiently  thin  to  show  coloured  rings. 

The  Hon.  Robert  Boyle  first  discovered  that  thin  bubbles  of  the  essential 
oils,  spirit  of  wine,  turpentine,  soap  and  water,  produce  the  colours,  and  he 


THE  INTERFERENCE  OF  LIGHT. 


1 29 


succeeded  in  blowing  glass  so  thin  that,  like  the  mica,  it  displayed  varieties  of 

colour. 

Lord  Brereton  observed  the  colour  of  thin  oxidized  or  decomposed  films,  such 
as  are  produced  by  the  action  of  the  weather  during  a  prolonged  period  on  the 
ancient  glass  in  church  windows,  or  on  glass  which  has  been  buried  in  the 
earth.  When  steel  is  tempered,  the  regular  gradations  of  colour  produced  by 
the  oxidation  of  a  very  thin  outer  film  are  a  guide  to  the  skilled  workman 
who  tempers  the  metal. 

Mr.  De  la  Rue,  by  floating  a  very'  thin  film  of  a  quick-drying  varnish  on 
the  surface  of  hot  water,  and  then  receiving  this  on  a  sheet  of  paper,  was 
enabled  to  secure  in  the  most  perfect  manner  those  lovely  tints,  which  are 
sometimes  associated  with  the  surface  of  ponds  into  which  greasy  matter  or 
oil  may  pass,  or  in  the  puddles  after  rain  in  th:  yard  of  a  gas-works  where 
liquor  containing  coal  oil  has  been  spilt. 

The  variety  of  colours  which  Newton  describes  in  his  important  “Table  of  the 
Colours  of  thin  Plates  in  Air,  Water,  and  Glass,”  arc  given  by  him  in  the  suc¬ 
cession  of  spectra  or  order  of  colours,  where  he  enumerates  seven  spectra  or 
orders  of  colours  ;  these  are  different  from  reflected  and  transmitted  rays,  and 
are  produced  by  thicknesses  of  air,  water,  or  glass,  estimated  from  a  scale  of 
an  inch  divided  into  one-million  parts. 


Fig.  1 1 7. —  Woodward's  Model  of  Waves ,  with  movable  Rods. 


Newton  measured  the  diameter  of  every  colourea  ring;  he  did  not  depend 
merely  upon  calculation,  but  tried  a  number  of  experiments  with  the  colours 
of  the  spectra,  allowing  each  to  fall  separately  on  his  apparatus,  and  dis; 
covered  that  under  these  circumstances  he  no  longer  obtained  a  variety  oi 
coloured  rings,  but  observed  that  the  central  dark  spot  was  surrounded  by 
rings  of  the  same  colour  as  the  light  incident  on  the  lenses  alternating  with 
dark  rings. 

Thus,  supposing  Newton  to  have  placed  the  apparatus  for  producing  the 
rings  into  the  yellow  part  of  the  spectrum,  there  would  be  a  dark  spot  in  the 
centre,  then  a  yellow  ring,  now  a  dark,  again  a  yellow  ring,  and  so  on  ;  he  then 
squared  the  diameters  ot  the  reflected  coloured  rays,  and  obtained  the  odd 
numbers,  1,  3,  5,  7,  9,  &c.,  while  the  square  of  the  diameters  of  the  dark  rings 
were  as  2,  4,  6,  8,  10,  &c.  When  the  rings  were  observed  by  transmitted 
light,  the  order  was  reversed — the  coloured  rings  being  at  the  even  numbers, 
and  the  dark  ones  at  odd  integers. 

These  effects  Newton  called  fits  of  transmission  and  fits  of  reflection  ;  they 
could  not  be  reconciled  or  explained  by  his  own  favourite  theory,  and,  to  the 
honour  of  this  great  philosopher,  he  did  not  attempt  to  press  the  co  puscular 
theory,  and  compel  it  to  his  own  use,  but  simply  left  behind  him  a  record  of 
facts,  only  naming  that  which  he  had  proved  to  exist,  and  giving  the  relative 
thicknesses  of  the  plates  of  air  by  which  each  colour  is  reflected. 

o 


i3° 


ON  LIGHT. 


The  undulatory  theory  of  light  alone  is  adopted  to  explain  these  phenomena, 
and  by  what  is  termed  the  interference  of  the  waves  the  effects  are  supposed 
to  be  produced.  Ingenious  models  have  been  made  to  explain  the  law  of 


Fig.  i  i  8. — A  Model  of  Fixed  Waves. 

interference;  but  those  of  Mr.  Charles  Woodward,  the  President  of  the  Isling¬ 
ton  Scientific  Society,  are  the  most  simple,  and  are  thus  described  by  him  in 
his  admirable  little  work  on  the  “  Polarization  of  Light 

A  B  (Fig.  1 17)  represents  a  model  with  rods  freely  moving  in  a  perpendicular 
direction  through  the  frame  A  B,  and  furnished  with  pins  resting  upon  the 


F  ig.  1 19. — Intensity  of  Waves  doubled  by  the  Superposition  and  Coincidence  of 

two  equal  Systems. 

upper  part  of  the  frame,  so  that  when  at  rest  the  whole  may  assume  the 
appearance  of  waves,  as  in  the  diagram. 

C  D  (Fig.  1 1 8)  represents  a  fixed  model  with  waves  of  similar  size  and 
intensity,  and  numbered  so  as  to  distinguish  each  half-undulation. 


Fig. 


120. —  Waves  neutralised  by  the  Superposition  and  Ititerference 

equal  Systems. 


of  two 


It  will  be  seen  that  when  the  stars  indicating  the  highest  point  of  the  waves, 
as  A  B,  correspond  with  the  odd  numbers  of  half-undulations  on  c  D,  each 
system  of  waves  will  be  in  the  same  state  of  vibration;  and,  if  so  superposed,  a 
series  of  waves  of  doubled  intensity  will  be  the  result,  as  in  Fig.  119. 


THE  INTERFERENCE  OF  LIGHT. 


If,  on  the  other  hand,  the  two  systems  be  so  superposed  as  that  the  stars 
on  A  B  shall  coincide  with  the  even  numbers  on  c  D,  as  in  Fig.  120,  there  will 
be  a  difference  of  half  an  undulation  in  the  two  systems  ;  the  one  will  neutra 
lize  the  other  by  interference,  and  darkness  will  be  the  result. 

If  C  D  be  continued  so  that  A  B  may  be  moved  forward  indefinitely,  it  will 
be  obvious  that  the  waves  will  be  equally  increased  in  intensity  by  a  difference 
in  the  two  systems  of  any  even  number,  and  neutralized  by  a  difference  of  any 
odd  number,  of  half-undulations.  These  models  are,  therefore,  well  suited  to 
teach  matter  of  fact,  viz.,  that  two  sets  of  waves  of  water  may  come  together 
and  obliterate  each  other,  as  in  the  tides  of  the  port  of  Batsha,  described  by 
Halley  and  Newton,  where  the  two  waves  arrive  by  channels  of  different 
lengths,  and  produce  a  smooth  surface ;  or  two  waves  of  light  may  com ' 
together  in  such  phases  that  in  one  case  they  exalt  each  other  and  produce 
a  wave  of  double  intensity,  and  in  the  other  phase  they  may  destroy  one 
another  and  cause  darkness.  A  wave  of  white  light  is,  however,  made  up  of  other 
waves  of  coloured  light  ;  so  that  when  such  a  complicated  series  of  different- 
colourcd  waves  interfere,  it  is  easy  to  perceive  that  certain  coloured  waves  may 
coincide  and  extinguish  each  other,  whilst  the  remaining  colours  may  unite 
and  intensify  each  other. 

That  waves  of  light  do  so  interfere  is  placed  beyond  all  doubt  by  the  expe¬ 
riments  of  Dr.  Young,  and  even  more  elaborately  by  the  following  beautiful 
experiment  devised  by  Fresnel: 


Fig.  1 2 1 -Fresnels  arrangement  to  show  the  Interference  of  the 

Waves  of  Light. 

A  sunbeam  from  the  Heliostat  is  passed  through  a  narrow  rectangular  slit 
in  the  shutter  (as  described  at  p.  87),  covered  with  red  glass  to  secure  a  mono¬ 
chromatic  light,  or  wave  of  simple  light.  The  red  light  is  brought,  by  a  cylin¬ 
drical  lens  of  very  short  focus,  to  a  point  at  A.  The  rays  cross  each  other 
and  fall  upon  two  mirrors  of  parallel  glass  B  C,  B  D,  placed  at  a  very  obtuse 
angle,  having  their  line  of  intersection  parallel  to  the  line  of  light.  After  re¬ 
flection  the  rays  proceed  as  if  they  came  from  the  two  points  F  F  behind  the 
two  mirrors;  they  interfere  at  G,  and  at  other  points  not  marked  out  in  the 

9—2 


1 32 


ON  LIGHT. 


diagram,  and  produce  light  and  dark  fringes ;  but,  if  one  of  the  beams  of  light 
proceeding  from  the  points  E  E  be  intercepted  by  a  screen,  the  whole  of  the 
alternations  of  red  and  dark  fringes  disappear,  and  the  only  light  left  is  that 
derived  from  the  single  ray  of  red  light  which  remains  after  the  other  was 
removed  by  the  screen.  In  this  diagram  two  sets  of  waves  only  are  used,  but, 
of  course,  the  same  law  applies  to  all. 

It  is  this  principle  of  interference  which  p  ociuces  coloured  fringes  by  inflexion 
or  diffraction,  such  as  rays  passing  along  the  edge  of  a  screen,  or  the  fringes 
at  the  edge  of  a  plane  mirror,  or  fringes  produced  by  narro'w  rectangular 
openings,  fringes  by  two  narrow  slits  very  close  together,  and  those  obtained 
through  gratings  or  networks.  The  word  grating  might  deceive  the  reader,  and 
lead  him  to  suppose  that  the  effect  was  caused  by  some  rough  arrangement ; 
but  these  beautiful  experiments  were  carried  out  by  Frauenhofer  by  tracing 
parallel  lines  on  a  film  of  gold  leaf  fixed  on  a  plate  of  glass,  and  look¬ 
ing  through  them  with  transmitted  light.  Nature  supplies  us  with 
striated  bodies,  which  are  in  effect  reflecting  gratings.  Brewster  calculated 
that  there  were  three  thousand  lines  in  an  inch  of  a  piece  of  iridescent 
mother-of-pearl.  But  this  number  has  been  surpassed  by  Barton,  who  ruled 
from  two  to  ten  thousand  lines  on  steel,  which  he  afterwards  hardened 
and  used  as  a  die  to  stamp  bright  brass  buttons.  These,  when  illuminated 
by  the  various  rays  emanating  from  the  numerous  lighted  wax  candles  in  a 
ball-room,  flashed  with  the  splendid  colours  of  the  diamond.  The  colours  of 
Newton’s  rings  are  due  to  the  interference  of  the  light  reflected  from  the  upper 
and  under  surface  of  the  film  of  air;  for,  however  thin  this  may  be,  it  must 
have  an  upper  and  an  under  surface,  like  a  sheet  of  paper. 

Let  Figs.  1 17  and  1 1 8,  pages  107,  108,  represent  two  equal  systems  of  waves 
from  red  light  reflected  to  the  eye  from  the  upper  and  under  surface  of  Newton’s 
thin  plates  of  air.  If  they  be  superposed,  as  in  Fig.  1 1 9,  page  108,  the  waves 
will  coincide,  and  there  will  be  red  light,  as  in  the  first  coloured  ring.  On 
moving  A  B  a  distance  equal  to  one  half-undulation  at  Fig.  120,  the  waves  will 
be  neutralized  by  interference,  and  there  will  be  darkness ;  on  moving  A  B  a 
second  half-undulation,  there  will  be  light,  and  so  on ;  for  when  the  stars  indi¬ 
cating  the  highest  part  of  the  waves  of  A  B  coincide  with  the  odd  numbers  of 
half-undulations  of  c  D,  there  will  be  light,  as  in  Fig.  119;  and  when  they 
coincide  with  the  even  numbers,  darkness  will  be  caused  by  interference,  as  in 
Fig.  120. 

Dr.  Young  proved  that  each  of  Newton’s  fits  of  transmission  and  reflection 
was  equal  to  half  a  wave  of  each  colour,  and  this  is  equal  in  length  to  the 
thickness  of  the  plate  of  air  at  which  that  colour  is  first  reflected,  and  there¬ 
fore  a  whole  undulation  would  be  equal  to  two  of  Newton’s  spaces  or  fits,  or 
what  he  termed  the  length  of  an  interval  between  the  fits  of  easy  reflection. 
Thus,  the  thickness  of  the  plate  of  air  required  to  produce  red  light  being 
determined  by  Newton  to  be  133  ten-millionths  of  an  inch,  double  that  number, 
or  the  length  of  a  wave  of  red  light,  would  be  266  ten-millionths  of  an  inch. 


For 

orange 

240 

ten-millionths  of 

an  inch 

99 

yellow 

227 

99 

99 

99 

green 

21 1 

99 

99 

99 

blue  . 

196 

99 

99 

9? 

indigo 

185 

99 

99 

9? 

violet 

167 

99 

» 

THE  INTERFERENCE  OF  LIGHT 


i33 


Herschel’s  table  is,  perhaps,  the  most  complete  record  of  the  invaluable 
work  of  Newton.  The  figures  are  Newton’s,  although  the  meanings  of  them 
have  been  altered  to  comply  with  the  undulatory  theory. 


Colours  of  the  Spectrum. 

Lengths  of  an  Un¬ 
dulation  in  parts 
of  an  inch. 

Number  of  Undu¬ 
lations  in  an 
inch. 

Number  of  Undulations 
.  in  a  second. 

Extreme  red 

0'0000266 

37,640 

45  8,000000,000000 

Red  . 

0'0000256 

39, 180 

477 ,000000,000000 

Intermediate 

o-oooo246 

40,720 

495,000000,000000 

Orange 

0'0000240 

41,610 

506,000000,000000 

Intermediate 

o’oooo235 

42,510 

5 1 7,000000,000000 

Y ellow . 

0'00002  27 

44,000 

q  q  ,000000,000000 

Intermediate 
Green  . 

0‘00002I9 
0'00002  I  I 

45,600 

47,460 

5  5  5,000000,000000 
577 ,000000,000000 

Intermediate 

0’0000203 

49,320 

600,000000,000000 

Blue 

O'OOOO I 96 

5  !,i IO 

622,000000,000000 

Intermediate 

o'oooo  189 

52,910 

644,000000,000000 

Indigo  . 

O'OOOO  1 85 

54,070 

658 ,000000,000000 

Intermediate 

o'oooo  1 8 1 

55,240 

67  2,000000,000000 
699,000000,000000 

Violet  . 

O'OOOO  174 

57,490 

Extreme  violet 

o'ooooi67 

59,750 

727 ,000000,000000 

A  very  good  idea  may  be  given  of  the  effect  of  the  law  of  interference  by  means 
of  a  simple  contrivance  proposed  by  Sir  Charles  Wheatstone,  called  the  Eido- 
trope.  It  is  made  of  two  circular  pieces  of  ordinary  perforated  zinc,  one  of  which 
is  made  to  turn  round  in  front  of  the  other  by  means  of  a  band  and  pulley,  the 
whole  being  arranged  as  an  ordinary  magic-lantern  slide.  Wire  gauze  or 
perforated  cardboard  may  be  substituted  for  the  perforated  zinc.  If  the  two 
zinc  plates  were  perforated  exactly  alike,  little  or  no"  effect  would  be  observed ; 
but  as  one  set  of  perforations  is  always  a  little  in  advance  of  the  other,  certain 
shadows,  which  assume  interesting  forms,  are  perceptible  when  the  instrument 
is  used  in  the  magic  lantern,  and  the  figures  projected  on  to  the  disc.  The 
dark  shadows  are  caused  by  the  mechanical  interference  of  the  zinc  plates  in 
the  proportion  to  represent  the  half-undulation,  and  in  some  positions  are  very 
distinct.  If  wire  gauze  is  employed,  the  shadows  assume  just  the  same 
appearance  as  the  surface  of  watered  silk. 


DOUBLE  REFRACTION  AND  THE  POLARIZATION  OF  LIGHT. 

When  a  ray  of  light  falls  upon  the  surface  of  Iceland  spar,  it  is  divided  into 
two  colourless  rays,  one  of  which  is  called  the  ordinary,  and  the  other  extia- 
ordinary,  ray  of  light ;  both  rays  possess  physical  properties  different  from 
those  which  belong  to  common  light,  and  if  reunited  they  would  again  form 
common  light. 


134 


ON  LIGHT. 


A  most  curious  fact,  showing  how  the  imponderable  forces  are  connected 
together,  is  demonstrated  by  the  experiments  of  Kerr,  of  Glasgow,  viz  ,  that  the 
property  of  double  refraction  is  developed  in  insulated  solids  and  liquids  when 
a  difference  of  “electrical  potential”  (or  degree  of  electrification,  positive  or 
negative)  is  maintained  between  opposite  surfaces,  as  by  induction,  in  which 
the  effect  of  an  electrical  body  is  to  raise  the  “electrical  potential”  of  all  other 
bodies  in  its  neighbourhood.  • 

In  the  year  1817,  Dr.  Young,  the  famous  revivalist  and  supporter  of  the  un- 
dulatory  theory,  whilst  considering  the  res  i’ts  of  the  sp  culations  of  Huygens, 
Wollaston,  and  Brewster,  and  the 
cause  of  double  refraction,  was  led  to 
believe  that  the  effect  must  arise  from 
a  difference  of  elasticity  in  the  crystal 
of  Iceland  spar;  and  being  aware 
that  Newton  had  expressed  the  idea 
that  a  ray  of  light  possesses  sides,  he 
first  proposed  the  hypothesis  of  trans¬ 
versal  vibrations  of  light.  The  theory 
is,  that  in  the  progress  of  a  ray  of  light 
the  forward  motion  is  made  up  of  two 
sets  of  vibrations,  which  are  either 
longitudinal  or  transversal.  The  longi¬ 
tudinal  vibrations  represent  the  path 
or  direction  of  theray,  whilst  the  trans- 
versalones  takeplaceat  right  anglesto  Fig.  122.  A  Rhomb  of  Iceland  Spar, 
the  former.  This  peculiar  motion  may  showing  the  double  Refraction  of  Light, 

be  compared  to  the  particles  of  water 

which  move  up  and  down  whilst  the  wave  advances  horizontally.  Dr.  Young 
illustrated  these  vibrations  by  the  propagation  of  undulations  along  a  stretched 
cord  agitated  at  one  end,  which  supposing  a  person  to  hold  in  his  hand,  and 
by  moving  first  quickly  up.  and  down,  a  wave  will  be  produced,  that  will  run 
along  the  cord  (see  p.  6)  to  the  other  end,  and  then  by  a  similar  movement, 
but  from  the  right  side  to  the  left,  another  wave  will  be  produced,  which  will 
run  along  the  cord  as  the  former;  but  the  vibrations  and  undulations  of  each 
will  be  in  planes  at  right  angles  to  each  other,  and  independent  of  each  other, 


Fig.  123. 

A,  Woodward’s  cardboard  model  representing  a  ray  of  common  light}  B,  transverse  section,  showing 

the  ligure  of  a  cross. 


one  being  in  a  perpendicular  plane  and  the  other  in  a  horizontal  plane,  so  that, 
according  to  this  theory,  A  (Fig.  1 23)  may  be  considered  to  represent  a  ray  of 
ordinary  or  unpolarized  light,  a  cross  section  of  which  would  give  the  simple 
figure  B,  it  being  understood  that  the  vibrations  take  place  in  planes  all  round 
the  direction  of  propagation. 

With  the  help  of  this  hypothesis  of  transversal  vibration,  double  refraction 
is  easily  explained,  and  is  put  into  the  most  concise  terms  by  the  editor  of 


THE  POLARIZATION  OF  LIGHT 


i35 


the  late  Dr.  Young's  lectures  :  “A  ray  of  light  falls  on  the  surface  of  a  crystal 
the  elasticity  of  which  is  different  in  different  directions.  The  motions  conse¬ 
quently  are  not  all  transmitted  with  the  same  velocity,  and,  as  the  index  of 
refraction  depends  on  the  velocity,  one  set  of  vibrations  will,  on  emergence,  be 
totally  separated  from  another.  Moreover,  the  light,  on  emerging,  is  quite 
different  from  common  light.  In  each  ray  it  consists  only  of  vibrations  in  one 
direction.  Suppose,  therefore,  one  of  these  rays  to  fall  on  a  second  crystal 
placed  in  a  similar  position  with  the  first  ;  it  will  not  now  be  divided  into  two, 
but  will  emerge  just  as  it  entered.  Light  which  consists  of  vibrations  in  one 
direction  is  called  polarized  light.  In  1810  it  was  discovered  by  Malus,  an 
officer  in  the  French  engineers,  that  light  reflected  from  the  same  face  of  unsil¬ 
vered  glass  is  more  or  less  polarized,  and  Brewster  ascertained  that  it  is  per¬ 
fectly  so  when  the  tangent  of  the  angle  of  incidence  is  equal  to  the  refractive 
index,  and  also  that  the  transmitted  ray  is  partially  polarized.” 

But  why  called  polarized  ?  The  term,  perhaps,  is  not  a  very  happy  one,  but 
was  suggested  by  analogy  to  the  poles  of  a  magnet. 

Dr.  Whewell  thus  defines  polarity:  “  Opposite  properties  in  opposite  direc¬ 
tions,  so  exactly  equal  as  to  be  capable  of  accurately  neutralizing  one  another.” 


Fig.  124. 

a,  magnet  made  of  watch-spring  with  north  and  south  poles;  n,  same  magnet  bent  round,  and  polarity 
neutralized;  c,  common  light;  D  D,  polarized  light. 


A  piece  of  steel  watch-spring,  when  magnetized,  has  a  north  and  south  pole 
(see  A,  Fig.  124);  but  when  the  same  piece  of  steel  is  bent  round  in  a  circle, 
as  at  B,  Fig.  124,  the  two  forces  neutralize  each  other,  and  the  polarity  is  gone. 
Such  a  circular  piece  of  steel  might  be  compared  to  common  light :  it  is  like 
the  section  of  a  hoop-stick,  C;  whilst  polarized  light  may  be  compared  to  the 
straight  steel  magnet  A,  or  to  a  lath.  A  hoop-stick  is  the  same  all  round ;  but 
a  lath  has  a  top  and  bottom  and  sides.  The  former  may  represent  common 
light,  and  the  latter  polarized  light ;  and  thus  polarization  is  simply  the  separa¬ 
tion  of  the  two  sets  of  undulations  or  vibrations,  D  D,  Fig.  124. 

When  common  light  is  passed  through  transparent  refracting  bodies  per¬ 
fectly  homogeneous  in  their  structure,  and  of  a  uniform  temperature  throughout, 
such  as  gases,  common  air,  pure  water,  annealed  glass,  jelly,  and  many  kinds 
of  crystallized  bodies,  the  form  of  whose  primitive  crystal  is  the  cube,  the  regular 
octahedron,  and  the  rhomboidal  dodecahedron,  such  as  alum,  common  salt,  or 
fluor  spar,  the  beam  of  light  is  refracted  singly;  but  in  nearly  every  other 
crystalline  body  the  rays  undergo  double  refraction,  and,  although  this  is  not 
apparent  at  once,  like  it  is  with  Iceland  spar,  the  property  of  double  refraction 
is  soon  discovered  by  using  polarized  light. 


j36 


ON  LIGHT. 


Polarized  light  may  be  obtained  in  four  different  ways,  viz. — 

Firstly,  by  reflection; 

Secondly,  by  simple  refraction ; 

Thirdl",  double  refraction; 

Fourt.n/,  by  transmission  through  a  plate  of  tourmaline,  slit  parallel  to  the 
axis  of  the  crystal. 

Thirty  years  ago,  Mr.  J.  F.  Goddard,  then  of  the  Polytechnic,  London, 
received  from  the  Society  of  Arts  a  silver  medal  for  his  apparatus  for 
experiments  on  polarizing  light.  The  description  which  accompanied 
the  apparatus  is  so  good  and  so  little  known,  that  the  writer  has  quoted  the 
most  important  part  of  it,  in  order  to  explain,  with  the  assistance  of  the  appa¬ 
ratus  invented  by  Mr.  Goddard,  this  most  difficult  branch  of  optical  science. 

Polarization  by  Reflection  and  Simple  Refraction. 

“  Polarization  may  be  effected  with  common  crown  glass,  either  by  ordinary 
reflection  or  refraction,  each  of  which  will  exhibit  the  same  effects.  In  order 
to  understand  this,  let  b  b  (Fig.  A  125)  represent  a  bundle  of  plates  of  common 


FlGS.  A  and  B  125. — Explanation  of  Polarization  by  Reflection  and  Simple 

Refraction. 


glass,  placed  so  that  a  ray  of  ordinary  light,  a  a ,  may  form  an  angle  of  incidence 
of  56°  45'  with  a  line  perpendicular  to  their  surface ;  then  the  light  reflected 
and  represented  as  passing  off  at  a  will  be  polarized  light ;  and  if  a  proper 
number  of  plates,  which  for  the  same  angle  of  incidence  is  twenty-seven,  be 
employed,  the  light  transmitted  at  c  will  be  polarized  also,  the  two  rays  pos¬ 
sessing  the  same  properties,  but  at  right  angles  to  each  other. 

“Thus  in  the  reflected  ray  d  the  vibrations  are  supposed  to  take  place  in  a 
perpendicular  plane,  this  being  a  bird’s-eye  view  (Fig.  B  125  being  a  horizontal 
view  of  the  same  thing),  whilst  in  the  refracted  ray  c  the  vibrations  are  per¬ 
formed  in  a  horizontal  plane.  This  will  be  easily  understood  on  analyzing 
either  of  the  rays,  which  may  be  done  by  the  same  means  as  that  by  which  the 
original  beam  is  polarized.  Thus,  supposing  we  experiment  with,  test,  or 


THE  POLARIZATION  OF  LIGHT 


J37 


analyze  the  reflected  ray  d,  in  which  the  vibrations  are  in  a  perpendicular 
plane,  when  it  is  made  to  fall  upon  a  second  bundle  of  glass,  h  h,  at  the  same 
angle  of  incidence,  and  the  glass  be  so  placed  that  the  reflection  may  again 
be  in  the  same  plane,  it  will  be  again  wholly  reflected,  as  at  d'  d\  and  none 
will  be  transmitted  or  refracted  through  the  second  bundle  of  glass,  for  the 
very  same  cause  that  produced  its  reflection  from  the  first  bundle,  viz.,  that 
the  vibrations  continue  parallel  to  the  reflecting  surfaces.  But  if  the  second 
bundle  of  glass  is  put  in  such  a  position  that  the  vibration  shall  be  performed 
in  a  plane  perpendicular  to  the  reflecting  surface  (which  may  be  done  by 
turning  it  round  90°  in  such  a  direction  that  the  ray  of  light  shall  be  the  axis 
on  which  it  turns,  and  always  making  the  same  angle  of  incidence),  then,  as 
soon  as  it  begins  to  turn,  the  reflected  light  will  begin  to  decrease  in  intensity, 
and,  as  it  decreases,  a  portion  will  begin  to  be  transmitted  or  refracted  through 
the  glass,  which  will  increase  in  the  same  ratio  as  the  reflected  light  decreases ; 
and  when  the  bundle  of  glass  has  turned  90°,  in  which  position  it  is  shown  at 


c' 


A,  Fig.  126,  as  a  bird’s-eye  view,  and  at  the  horizontal  view,  B,  Fig.  126,  the  light  d 
is  wholly  transmitted  or  refracted  at  c‘  c,  no  portion  being  reflected.  In  such  a 
position  the  vibrations  will  be  in  a  plane  perpendicular  to  the  reflecting  surface ; 
and  such  vibrations  are  always  transmitted,  and  not  reflected,  as  we  also  see 
has  taken  place  in  the  polarization  of  the  original  beam  of  common  light  at  A, 
Fig.  125,  before  referred  to.  Now  let  the  second  bundle  h  h,  B,  fig.  126,  con¬ 
tinue  to  turn ;  it  will  be  seen  that,  as  soon  as  it  begins  to  move,  the  transmitted 
c  c'  will  begin  to  decrease,  a  portion  beginning  to  be  again  reflected,  which,  as  the 
glass  turns,  will  increase  in  intensity  in  the  same  ratio  as  the  transmitted  light 
decreases,  until  it  has  turned  another  90°,  or  reached  180  from  the  first  posi¬ 
tion,  as  seen  at  c,  Fig.  126,  when  the  plane  of  reflection  is  again  parallel  to  the 
plane  in  which  the  vibration  takes  place;  consequently  the  whole  light  is  again 
reflected  at  d'  d\  none  being  transmitted,  from  the  same  reason  as  betore 
stated.  On  continuing  the  revolution,  the  same  thing  occurs  at  each  quadrant 
of  the  circle.  In  Fig.  D  126  the  bundle  of  glass  h  h  is  represented  as  having 
turned  270°,  or  three-quarters  of  a  circle,  in  which  position  the  same  thing  occurs 
at  90°,  when  the  light  d  is  wholly  refracted  and  transmitted  through  glass, 
as  at  cc;  so  that  it  is  evident,  in  these  experiments,  that  there  are  two  posi¬ 
tions,  shown  in  Figs.  125  and  126,  in  which  the  same  ray  ol  polarized  light  ^/is 
wholly  reflected,  as  at  d' d1,  and  two  other  positions,  A,  D,  h  igs.  125  and  126,  in 


138 


ON  LIGHT. 


which  it  is  wholly  transmitted  by  the  analyzing  bundle  of  glass,  as  at  c'c',  all 
of  which  are  easily  understood  by  bearing  in  mind  the  description  of  the 
physical  nature  of  common  light  according  to  the  undulatory  theory,  and  the 
action  of  the  first  or  polarizing  bundle  of  glass,  or  transversal  vibrations. 

“  Thus  we  obtain  experimental  data,  which  may  be  expressed  as  follows : 


POLARIZED  LIGHT 

1.  Is  capable  of  reflection  at  oblique 
angles  of  incidence  in  certain  positions 
only  of  the  reflector. 

2.  Will  pass  through  a  bundle  of 
plates  of  glass  only  when  they  are 
placed  in  certain  positions. 

3.  Does  not  pass  through  a  plate 
of  tourmaline  cut  parallel  to  the  axis 
of  the  crystal,  except  in  certain  posi¬ 
tions;  in  others,  the  tourmaline,  though 
quite  transparent,  stops  the  whole  of 
the  polarized  light  as  if  it  was  opaque. 

“  A  bundle  of  plates  of  glass  or  a  slice  of  tourmaline  is  consequently  to  be 
regarded  as  a  test  of  polarized  light,  and  enables  the  physicist  to  distinguish 
between  the  latter  and  common  light,  which  he  is  said  to  analyze,  the  bundle 
of  glass  or  the  tourmaline  being  called  the  analyzer. 


COMMON  LIGHT 

1.  Is  capable  of  reflection  at  oblique 
angles  of  incidence  in  every  position 
of  the  reflector. 

2.  Will  pass  through  a  bundle  of 
plates  of  glass  in  any  position  in 
which  they  may  be  placed. 

3.  Passes  through  a  plate  of  tour¬ 
maline,  cut  parallel  to  the  axis  of  the 
crystal,  in  every  position  of  the  plate. 


Polarization  bv  the  Tourmaline. 

“Amongst  crystallized  minerals  there  are  many  possessing  the  property  of 
polarizing  the  light  transmitted  through  them,  the  most  remarkable  of  which, 
however,  is  the  tourmaline.  This  mineral  crystallizes  in  long  prisms,  whose 
primitive  form  is  the  obtuse  rhomboid,  having  the  axis  parallel  to  the  axis  of 
the  prism. 

“  It  must  be  remembered  also  that  the  axis  of  crystals  is  not,  like  the  axis  of 
the  earth,  a  single  line  within  the  crystal,  but  a  single  direction  through  the 
crystal;  for  supposing  Fig.  127  to  represent  a  crystal  of  any  kind,  the  axis  of 


A 


Fig.  127. 


Fig.  128. 

A,  single  plate  of  tourmaline;  n.  superposition  of 
the  second  plate  on  the  first. 


which  is  in  the  direction  A  x,  if  we  divide  such  a  crystal  into  four  along  the 
lines  B  B  and  c  C,  each  separately  will  have  its  axis  A  O,  O  x,  c  B,  and  B  C, 
which,  when  united  in  one  crystal,  are  all  parallel;  every  line,  then,  within  the 
crystal  parallel  to  A  X  is  an  axis. 


THE  POLARIZATION  OF  LIGHT 


l39 


“If  we  cut  a  crystal  of  tourmaline  of  a  proper  kind  parallel  to  the  axis  into 
thin  plates  of  an  uniform  thickness  (about  one-twentieth  of  an  inch),  and 
polish  each  side,  it  possesses  the  property  of  polarizing  light  transmitted 
through  it  in  a  remarkable  manner.  Fig.  A  128  represents  one  of  these  plates, 
the  lines  across  which  we  may  suppose  to  be  parallel  to  the  axis.  Now,  if  we 
hold  such  a  plate  before  the  eye,  and  look  at  the  light  of  the  sun,  or  flame  of 
a  candle,  or  any  artificial  light,  a  great  portion  will  be  transmitted  through  the 
plate,  which  will  appear  quite  transparent,  having  only  the  accidental  colour 
of  the  crystal,  which  in  specimens  suited  for  these  experiments  is  generally 
brown  or  green;  but  the  light  so  transmitted  will  be  polarized  light,  and,  on 
being  analyzed  by  a  second  plate,  which  may  be  done  by  looking  through 
both  at  the  same  time,  we  shall  find  that  when  the  axes  of  both  plates  coincide, 
l.c.,  are  parallel  with  each  other,  the  light  which  is  passed  through  the  first 
will  also  freely  pass  through  the  second,  and  they  will  together  appear  per¬ 
fectly  transparent ;  but  when  one  is  turned  round,  so  that  the  axes  of  each 
plate  are  at  right  angles  (across  each  other),  as  represented  in  B,  Fig.  128, 
not  a  ray  of  light  will  pass  through — they  will  appear  perfectly  opaque, 
although  we  may  be  looking  at  the  meridian  sun.  If  we  suppose  the  structure 
of  the  crystal  to  be  represented  by  a  grating,  the  bars  of  which  are  the  axis, 
we  may  conceive  that  its  action  on  ordinary  light  will  be  to  transmit  such 
vibrations  only  as  are  performed  in  a  plane  parallel  with  the  axis,  and  to  stop 
all  others.  Hence,  the  light  transmitted  through  a  single  plate  will  be  polar¬ 
ized,  and  possess  exactly  the  same  properties  as  the  light  polarized  by  any  other 
means,  as  may  be  proved  by  analyzing  it  by  any  of  the  means  which  have 
been  described.  But  let  us  suppose  a  second  tourmaline  to  be  used,  and,  as 
it  is  understood  that  in  the  light  which  makes  its  way  through  the  first  tour¬ 
maline  the  vibrations  are  parallel  to  the  axis,  all  other  vibrations  being  stopped 
when  the  axis  of  the  second  or  analyzing  plate  is  perpendicular  to  the  first,  as 
represented  in  B,  Fig.  128,  the  vibrations  which  have  passed  through  the  first, 
being  now  perpendicular  to  the  second,  will  also  now  be  stopped  by  the  second 
plate  in  such  a  position;  and,  as  it  is  turned  round,  there  will  be  found  two 
positions  in  which  it  will  not  pass  through,  being  wholly  stopped,  these  posi¬ 
tions  being  at  right  angles  to  each  other,  as  will  be  understood  by  B,  fig.  128, 
where  a  a  is  the  first  or  polarizing  plate,  and  c  the  second  or  analyzing  plate, 
overlapping  the  first.” 

Mr.  Goddard  then  describes  the  instrument  for  which  he  received  the  silver 
medal — the  oxy-hydrogen  polariscope.  (Fig.  129.) 

“  In  this  instrument  a  represents  the  hydro-oxygen  blowpipe;  B,  the  lime 
cylinder  and  diverging  rays  of  light  refracted  by  the  condensing  lenses  c  c  c  and 
falling  upon  a  mirror  bb,  composed  of  ten  plates  of  thin  flattened  crown  glass 
placed  in  the  elbow  of  a  tube  bent  to  the  polarizing  angle  of  crown  glass ;  d, 
converging  rays  of  polarized  light  reflected  from  the  mirror;  hit,  a  bundle  of 
sixteen  plates  of  mica,  for  analyzing  the  light  previously  polarized  by  reflec¬ 
tion  ;  e,  a  double-refracting  crystal  (film  of  selenite)  placed  in  the  focus  of  the 
object-glass  I,  which  forms  an  image  of  the  crystal  upon  a  disc  or  screen  at  r. 
As  the  analyzing  bundle  of  mica,  h  ) 1 ,  is  made  to  revolve  (or  turn  round),  the 
image  of  the  selen.te  upon  the  disc  undergoes  all  the  changes,  and  exhibits 
alternately  the  primary  and  complementary  colours  at  the  same  time ,  one  being 
reflected  in  the  direction  s,  and  the  other  transmitted  and  seen  at  r. 

“The  great  advantage  of  polarizing  the  light  from  a  number  of  plates  is  the 
obtaining  a  beam  of  any  required  dimensions,  of  much  greater  intensity  than 


ON  LIGHT. 


140 


# 


Fig.  129. — Goddard's  Oxy-hydrogen  Polariscope. 


by  any  other  means;  for  whatever  single  surface  may  be  employed  that 
polarizes  light  at  the  same  angle  as  the  glass  used  (which  for  crown  glass  is 
56’  45  ),  we  obtain  an  additional  quantity  by  laying  on  it  a  single  plate  of  such 
glass,  and  a  further  quantity  by  the  addition  of  a  second,  third,  or  any  further 
number ;  the  quantity  of  light  added  by  each  succeeding  plate  being,  how¬ 
ever,  less  in  proportion  to  the  number  of  plates  through  which  it  has  pre¬ 
viously  to  pass.  In  this  respect  the  single-image  (Nicol’s)  prism  of  Iceland 
spar  is  decidedly  the  best  for  analyzing,  as  by  this  a  great  variety  of  objects 
may  be  exhibited.  Its  application  is  shown  in  Fig.  130,  where  e,  the  selenite, 


THE  POLARIZATION  OF  LIGHT 


141 


is  placed  in  the  rays,  d  d  d,  of  polarized  light,  an  image  of  which  is  projected  by 
the  lenses  ;  h  is  the  analyzing  prism  through  which  the  rays  of  light  r  r  are 
refracted.” 


Fig.  130. — Use  of  the  Nicol's  Prism  as  an  Analyser. 

By  using  a  Nicol’s  prism  for  polarizing  the  light,  and  another  for  analyzing, 
the  most  brilliant  effects  can  be  produced  upon  the  ocean.  The  only  draw¬ 
back  is  the  expense  of  the  prisms  when  large  ones  are  used  ;  perhaps  the 
largest  ever  made  were  those  constructed  for  William  Spottiswoode,  Esq.. 
F.R.S.,  of  which  he  has  kindly  given  the  following  description  : 

41  Grosvknor  Placr, 

4 tk  June,  1877. 

Dear  SIR, — Tn  answer  to  your  inquiry  about  my  polarizing  apparatus,  I 
may  perhaps  explain  that  I  have  two  principal  sets,  each  of  which  has  in  its 
own  way  some  special  interest.  The  first  consists  of  a  pair  of  Nicol’s  prisms 
furnished  to  me  by  Mr.  Ladd,  having  a  clear  field  of  2\  in.  in  diameter.  These 
were  the  first  of  a  large  size  ever  constructed.  The  spar  is  of  perfect  purity, 
and  their  construction  is  excellent.  They  have  been  lent  to  and  used  by 
many  distinguished  men  for  special  researches,  as  well  as  for  lectures  in 
London  and  elsewhere.  They  accompanied  Prof.  Tyndall  on  his  lecture  tour 
in  the  United  States  in  1871.  They  were  the  starting-point  for  the  constiuction 
of  others  approaching  them  in  size,  and  on  this  account  they  have  a  kind  of 
historical  interest. 

One  main  obstacle  to  obtaining  Nicol’s  prisms  of  this  calibre  consists  in 
the  difficulty  of  finding  spar  in  pieces  of  sufficient  magnitude  and  purity  for 
the  purpose.  Through  the  kindness  of  my  friend  Prof.  Maskelyne,  in  the  first 
instance,  1  have  been  on  several  occasions  in  direct  communication  with  the 
owner,  or  lessee  under  the  Danish  Government,  of  the  mines  in  Iceland,  and 
have  had  the  opportunity  of  the  choice  of  some  magnificent  specimens  in  the 
rough.  In  the  selection  of  promising  crystals,  as  well  as  in  the  first  splitting 
them  into  blocks,  to  be  afterwards  cut  and  polished  for  optical  purposes,  great 
judgment  and  experience  are  requisite  ;  and  in  this  part  of  the  business  I 
have  received  most  valuable  assistance  from  Prof.  Maskelyne  himself,  and 
also  from  Mr.  C.  Ahreus,  who  subsequently  constructed  for  me  some  other 
pi  isms,  the  largest  as  yet  ever  made. 

From  a  block  of  spar,  sent  first  to  the  London  Exhibition  in  1861,  and 
subsequently  shown  at  Paris  in  1874,  Mr.  Ahrens  constructed,  under  the 
direction  of  Messrs.  Tisley  and  Spiller,  a  grand  prism,  having  a  field  of  3  ,’  in. 
clear  in  diameter.  The  magnitude  and  weight  of  this  prism  proved  so 
cumbrous,  that  Mr.  Browming  subsequently,  at  my  suggestion,  made  others 
for  me,  which  were  reduced  to  cylinders  by  cutting  away  all  the  spar  beyond 
that  comprised  in  the  circular  field  of  view.  But  convenient  as  this  form  was 
from  its  compactness,  it  proved  very  difficult  to  support  the  two  halves  in  their 


142 


ON  LIGHT 


relative  position,  and  to  prevent  them  sliding  over  one  another,  thereby  causing 
a  displacement  of  the  balsam  or  other  refracting  medium  interposed  between 
the  parts.  In  the  prisms  last  constructed  for  me  by  Mr.  Ahreus  the  cylindrical 
form  was  replaced  by  an  octagonal  form,  whereby,-  with  very  little  additional 
diameter  and  weight,  a  good  support  was  provided  for  the  two  parts,  and  the 
objection  above  mentioned  removed. 

My  principal  pair  are  now  octagonal ;  the  polarizer  has  a  clear  field  of  3f  in. 
in  diameter,  the  analyzer  one  of  3!  in.  The  focussing  lens  used  with  parallel 
light  is  achromatic,  and  is  best  placed  between  the  prisms  ;  on  this  account 
the  analyzer  may  for  many  purposes  be  somewhat  smaller  than  the  polarizer. 
Both  this  pair  of  prisms,  and  that  first  described,  are  furnished  with  a  system 
of  lenses  for  projecting  the  rings  shown  by  crystals  with  convergent  light.  But 
in  these  phenomena  the  advantage  of  the  larger  prisms,  which  transmit  fully 
half  as  much  more  light  than  the  smaller,  is  very  apparent. 

In  addition  to  the  apparatus  above  mentioned,  which  together  forms  a 
polariscope  proper,  I  have  succeeded  in  collecting  a  series  of  plates,  wedges, 
&c.,  of  quartz  and  of  Iceland  spar,  of  dimensions  and  of  workmanship  worthy 
of  the  polariscopes  for  which  they  are  adapted.  Among  these  I  may  men¬ 
tion  in  particular  a  set  of  quartz  plates  cut  perpendicularly  to  the  axis. 
Three  objects  are  of  peculiar  construction,  and  on  that  account  deserve 
mention.  First,  a  pair  of  circular  plates,  one  of  right-handed,  the  other 
of  left-handed  quartz,  each  composed  of  sectors  of  different  thicknesses  ; 
each  sector  consequently  shows  a  different  colour  for  each  position  of  the 
analyzer.  With  a  proper  adjustment  the  two  plates  will  neutralize  one 
another.  One  of  the  sectors  is  sufficiently  thin  to  show  low  tint  colours  by 
comparison  with  the  others,  and  thus  to  exemplify  Helmholtz’s  explanation  of 
russet,  browns,  drab,  peacock-blue,  &c.,  by  low  illumination.  Secondly,  a 
pair  of  quartz  plates,  cut  parallel  to  the  axes,  one  convex,  the  other  concave. 
The  convex  plate  replaces  the  thin  plate  usually  employed  in  connection  with 
the  concave,  and  heightens  or  varies  the  effects.  Thirdly,  and  this  is  perhaps 
the  most  remarkable  feat  of  constructive  skill,  a  pair  of  quartz  cones  (the  axes 
of  which  are  parallel  to  that  of  the  crystal),  one  hollow  of  right-handed,  the 
other  solid  of'  left-handed  quartz,  fitting  accurately  into  one  another.  These 
show  coloured  rings,  similar  in  their  general  features  to  those  in  the  last- 
mentioned  arrangement  ;  but  on  turning  the  analyzer  in  one  direction  or  in 
the  other,  the  rings  continuously  expand  or  contract. 

Quarter  undulation-plates  of  commensurate  size  have  been  added  to  the 
collection. 

I  remain,  dear  sir, 

Veiy  truly  yours, 

Prof.  Pepper.  W.  Spottiswoode. 

“  But  there  is  one  class  of  phenomena,  viz.,  the  rings  seen  to  encircle  the 
optic  axes  of  crystals,  the  number  of  which  increases  in  some  crystals  (the 
topaz,  for  instance)  with  the  divergence  of  the  rays  of  polarized  light  passing 
through  them.  It  will  be  evident,  then,  that  the  tourmalines  enable  us  to 
exhibit  more  of  these  rings,  and  upon  a  larger  scale,  than  the  prism,  which 
will  be  better  understood  by  the  arrangement  shown  in  Fig.  131. 

11  d d d ,  converging  rays  of  light  polarized  by  reflection  ;  /,  a  lens  of  short  focus, 
transmitting  a  cone  of  light  with  an  angle  of  divergence  horn  its  ray  r  r  of 
450  ;  e,  a  crystal,  say  topaz  ;  h,  the  tourmalines  for  analyzing  ;  so  that,  even  for 


THE  POLARIZATION  OF  LIGHT. 


*43 


these  purposes,  the  cost  of  the  tourmalines  is 'reduced  one-half  by  Goddard’s 
polariscope,  as  only  one  need  be  used.” 

The  writer  frequently  uses  Goddard’s  instrument  as  made  by  Mr.  Darker, jun. 
of  Paradise  Street,  Lambeth,  whose  father  before  him  earned  so  much  credit 
in  the  practical  parts  of  this  branch  of  optics.  Darker  also  makes  the  most 
elaborate  and  beautiful  designs  in  selenite  or  sparry  gypsum,  being  the  native 
crystallized  hydra¬ 
ted  sulphate  of 
lime,  from  which 
plaster  of  paris 
can  be  made  by- 
driving  off  the 
water  of  crystalli¬ 
zation.  This  mine¬ 
ral,  split  into  thin 
films,  and  cut 
under  water,  or 
oil,  or  turpentine, 
is  laid  upon  glass 
with  Canada  bal¬ 
sam.  The  greatest 
nicety  is  required 
in  the  manufacture 
of  the  selenite 
slides,  or  else  all  the  edges  of  the  figures  would  be  rough. 

A  piece  or  film  of  selenite  of  unequal  thicknesses  exhibits  the  most  varied 
and  beautiful  colours  when  placed  in  the  polariscope,  the  colours  transmitted 
by  the  analyser  being  complementary  to  those  reflected  from  the  bundle  of 
glass  plates.  Any  transparent  substance  in  which  unequal  elasticities  occur 
will  present  phenomena  of  colour  when  placed  in  the  polariscope.  A  piece 
of  plate  glass,  if  well  annealed,  shows  no  colour  until  it  is  bent  or  squeezed  by 
being  placed  in  a  strong  frame  provided  with  a  screw. 


FlG.  132 .—Apparatus for  compressing  Glass. 

a  a,  the  press  ;  n,  the  piece  of  plate  glass. 


On  the  same  principle,  unannealed  glass  exhibits  some  of  the  most  vivid 

colours  and  figures.  (Fig.  133.)  ,  ,  .  ,  ...  „ 

Or  if  a  rod  of  plate  glass  is  placed  in  the  polariscope  and  heated  with  a 
red-hot  copper  bar,  the  unequal  expansion  of  the  particles  causes  that  retar¬ 
dation  in  the  path  of  the  rays  which  results  in  interference,  and  the  proc  ac¬ 
tion  of  colours,  and  these  disappear  gradually  when  the  hot  copper  bar  is 
removed.  A  little  jelly  allowed  to  solidify  in  a  proper  frame,  the  sides  of 
which  are  of  glass,  exhibits  no  double  refracting  power  until  it  is  subjected 
to  pressure. 


ON  LIGHT 


1  44 


A  quill  pen  flattened  out  and  arranged  for  exhibition  in  the  polariscope  will 
give  some  very  pleasing  tints. 

Water  of  an  uniform  temperature  has  no  double  refracting  power,  but  when 
frozen  and  converted  into  ice 
the  particles  exhibit  unequal 
elasticities,  and  colour  is  the 
result  when  it  is  placed  in 
the  polariscope. 

If  plates  of  selenite  or  any 
doubly  refracting  crystal  of 
considerable  thickness  be 
ground  away  on  one  edge, 
so  as  to  give  them  a  wedge- 
shape,  they  will  present  bands 
or  fringes  composed  of  alt  the  colours  of  Neyvton’s  table,  arising  from  the 

iyn  a  5m^kSCaWhlCll  Suchf  a  shape  Possesses  ;  or  by  grinding  a  concavity 
in  a  similar  plate  a  number  of  concentric  rings  (reminding  the  spectator  of 

1  ewton  s  rings)  are  produced.  Small  crystals  obtained  by  evaporating  single 

oX  tS ’  f,  °f  ?Ceta,e  °f  zinc-  chlorate  of  P°‘“h.  sulphate  of 3' 

D0tissium\r  mie  h  “"IT"'!!’  ?ulPhate  of  “W,  borax,  ferrocyanide  of 
potassium,  &c., may  be  exhibited  in  the*  polariscope. 

shown  l  vrilrlS  obU[ne^  by  usan«  uniaxial  and  biaxial  crystals  are  well 
shown  by  Goddard  s  apparatus,  with  a  large  Nicol’s  prism  or  a  good  tourmaline 


Fig.  133. — Unannealed  Glass. 


MM 


V//HJ 

yy/// 

w 


Fig.  134. 

k,!l7nTrr'  Ti°  exhlblt  tb?so  coloured  rings  a  higher  microscopic  power 
is  used.  I  his  is  always  supplied  with  the  instrument,  and  Is  put  on  before 

pmml!l'e«  Polansc°Pe-  For  these  experiments  Iceland  spar,  rock  crystal, 
emu  aid,  sapphire,  beryl,  ice,  furnish  good  examples  of  uniaxial  crystals. 

_J Vnrfinn  arfe  i?Umber  of  crystals.  are  biaxial,  and  have  two  axes  of  double 
retraction,  which  are  more  or  less  inclined  to  each  other.  These  are  termed 

0,'CryStals  W’th  ,two  °Ptic  axes-  Nitrate  of  potash  exhibits* 
and  many  other?'  Y  pcrfecty>  also  Rochelle  salt,  selenite,  sugar,  borax, 

qollwhiff  b^dfS  obtained  from  biaxial  crystals  are  not  concentric,  but 
somewhat  oval,  with  two  centres,  which  represent  the  two  axes  of  the  crystal. 


THE  POLARIZATION  OF  LIGHT. 


T45 


The  splendid  phenomena  of  colours  produced  by  various  substances  in 
polarized  light  are  the  results  of  transversal  vibrations.  When  a  single  wave 
or  vibration  in  anyone  plane  is  divided  into  two,  at  right  angles  to  each  other, 
one  will  of  necessity  be  half  a  wave  behind  the  other,  the  two  being  opposite 


Double  curves  or  sets  of  elliptical  or  oval-like  rings  produced  by  a  plate  of  nitre  1-12  or  1-15  in.  thick, 

cut  perpendicular  to  the  prismatic  axis. 


halves  of  the  same  wave  ;  and  as  each  of  these  again  is  divided  or  resolved 
into  two  others,  there  will  be  four  waves  or  vibrations  produced  from  the 
original  one.  Two  of  these  in  one  plane  coincide  and  strengthen  each  other, 
while  the  two  in  the  other  plane  oppose  and  destroy  each  other. 

This  difficult  subject  may  be  summed  up  and  concluded  wfith  Woodward’s 
very  instructive  diagrams,  exhibiting  at  one  view 

POLARIZATION, 

ANALYZATION, 

INTERFERENCE  OF  LIGHT. 


Fig.  x36.— a,  b,  C.  d,  common  light ;  E,  a  plate  of  tourmaline,  or  a  bundle  of  plates  of  glass,  termed 
the  polarizer  ;  f,  polarized  light ;  g,  a  plate  of  selenite ;  h,  dipolarized  light;  1,  a  plate  of  tourmaline, 
or  a  bundle  of  thin  plates  of  glass,  called  the  analyzer  ;  k,  coincidence  of  waves  for  red  light ;  l,  inter¬ 
ference  of  waves  for  yellow,  and  M,  of  those  for  blue  light ;  n,  the  result-red  hgh.t-,  . 

Fig.  137.— 1,  the  analyzer  turned  round  90°;  K,  interference  of  waves  for  red  light;  l,  coincidence 
of  waves  for  yellow,  and  M,  those  for  blue  light ;  N,  the  result  green  light. 


10 


HEAT. 


THERMOMETRIC  HEAT. 

AMONGST  the  physical  forces,  the  corellation  of  which  has  been  so  well 
discussed  by  various  philosophers,  that  termed  calot'ic  (at  one  time,  like 
light,  considered  to  be  a  direct  emanation  of  some  rare  and  subtle  form  of 
matter)  has  received  the  most  careful  attention.  Light  is  discoverable  by  two 
most  sensitive  inlets — the  eyes.  The  sensation  termed  heat  is  not  more 
appreciable  by  the  eyes  than  by  any  other  part  of  the  human  body,  and  yet  the 
mind  may  be  easily  deceived  by  sensations  caused  by  heat  or  its  absence, 
termed  cold.  The  body  may  experience  the  greatest  torture  by  an  excess  of 
heat  or  burning,  and  it  may  derive  pleasure  from  the  application  of  a  moderate 
amount  of  the  same  power,  as  in  the  use  of  the  Turkish  or  other  baths. 

The  nervous  system  distributed  over  the  surface  of  the  body  cannot,  how¬ 
ever,  distinguish  properly  degrees  of  heat,  and  we  seem  to  be  able  to  discover 
only  when  heat  is  entering  or  leaving  our  bodies,  and  then  the  exclamations 
referring  to  extremes,  such  as  “  how  hot  "  or.  *'how  cold !  ”  escape  us.  And  even 
this  faculty  is  limited,  because  the  sensations  caused  by  touching  a  lump  of 
frozen  mercury  and  a  hot  iron  are  the  same.  The  unfortunate  person  who 
does  this  will  complain  as  if  he  were  burnt  with  the  intense  cold  of  solid 
mercury.  We  cannot,  as  with  the  eye  or  the  ear  with  light  and  sound, 
discern  gradations  of  heat ;  hence  artificial  means  have  been  invented  to 
supply  this  want. 

It  is  not  surprising  that  heat  should  have  been  considered  to  be  a  material 
body,  entering  into  combination  with  solids,  fluids,  or  gases,  because  it  is  so 

146 


THERMOMETRIC  HEAT 


M7 


readily  evoked  from  ponderable  substances.  A  clever  blacksmith,  with  his 
hammer,  anvii,  and  a  rod  of  good  iron,  will  dexterously  obtain,  by  hammering 
the  metal,  enough  heat  to  light  his  forge  fire,  provided  a  little  sulphur  is  used 
as  the  intermediate  combustible  body. 

A  very  instructive  and  beautiful  modification  of  the  blacksmith’s  handicraft 
has  been  devised  by  Mr.  Cecil  Wray. 

It  is.  well  known  that  when  a  smart  blow  is  given  with  a  hammer,  some 
portion  of  the  mechanical  energy  is  converted  into  heat  ;  but  perhaps  it  is 
not  generally  known  that  a  portion  of  the  heat  so  generated  is,  in  its  turn, 
converted  into  electricity. 

The  means  of  showing  that  a  thermo-electric  current  is  actually  present  is 
very  simple ;  it  is  only  necessary  to  connect  a  block  of  antimony  to  one  terminal 
of  a  reflecting  galvanometer  of  low  resistance,  and  to  connect  an  iron  hammer 
by  means  of  a  flexible  wire  to  the  other  ;  when  the  antimony  is  hit  with  the 
hammer,  a  slight  deflection  may  be  observed  on  the  galvanometer  scale. 

C 


a,  hammer  with  wire  attached  ;  b,  block  of  antimony ;  c,  galvanometer. 

The  peculiar  interest  of  this  experiment  is  not  so  much  in  the  changes  of 
force  as  in  the  infinitely  short  space  of  time  in  which  these  complicated 
changes  are  effected. 

According  to  Mr.  R.  Sabine,  the  time  occupied  in  striking  an  anvil  with  a 
small  hammer,  held  in  one  hand,  is  only  50  millionths  of  a  second  ;  therefore, 
in  TTHHlbtro0^  a  second,  mechanical  energy  passes  into  heat —heat  into  electri¬ 
city — electricity  into  magnetism— magnetism  into  motion. 

The  above  sketch  shows  the  arrangement,  and  the  arrows  the  direction  of 
the  current. 

The  galvanometer  used  was  wound  with  thick  wire,  and  had  a  resistance 
of  16  ohms,  and  the  needle  and  mirror  together  weighed  3  grains. 

It  is  probable  that  copper  would  be  better  than  antimony  to  use  as  an  anvil. 
In  this  case,  of  course,  the  current  would  be  in  the  reverse  direction  to  that 
shown.  10 _ 2 


i48 


HEAT. 


If  the  hammer  is  allowed  to  remain  on  the  anvil  after  the  blow  is  struck,  a 
very  considerable  deflection  is  obtained  ;  and  if,  instead  of  striking  the  anti¬ 
mony  with  the  hammer,  the  latter  be  sharply  rubbed  upon  the  former,  a  still 
more  powerful  current  is  obtained. 

Heat  travels  with  light  from  the  sun  ;  and  as  Newton  succeeded  in  con¬ 
vincing  his  contemporaries  that  the  latter  was  a  material  body,  it  came  to 
pass  by  a  natural  sequence  of  reasoning  that  the  former  should  also  be 
regarded  as  a  subtile  rare  form  of  matter  opposed  to  cohesion.  The  material 
theory  of  caloric — the  hypothesis  of  “emission” — has  given  way  to  the  more 
rational  theory  of  “undulation.”  If,  as  has  been  explained  at  p.  I,  an  im¬ 
ponderable  elastic  ether  pervades  all  space,  a  peculiar  vibratory  motion  set 
up  in  the  material  particles  of  a  body  may  be  communicated  to  this  ether; 
and  then,  on  the  same  principle  that  a  glass  trembles  whilst  producing  sound 
in  air,  so  the  minute  particles  or  molecules  of  solid  fluids  or  gases  oscillate, 
and  these  oscillations  or  vibrations  are  communicated  to  and  transmitted  by 
the  ether.  Physicists,  however,  prefer  to  speak  of  their  favourite  hypothesis 
as  “The  Dynamical  Theory”  (Sava/xis,  power).  The  title  at  once  shows  that 
heat,  and  not  light,  is  intended  to  be  expressed.  Heat  is  in  every  sense  of  the 
word  a  “  power  the  terms  are  mutually  convertible  the  one  into  the  other. 
The  combustion  of  coal  produces  heat,  which  generates  steam,  and  the  latter 
is  the  greatest  modern  representative  of  power. 

Power,  as  shown  by  the  muscular  force  of  the  arm  conveyed  through  a 
hammer,  generates  heat  when  metals  are  beaten  on  the  anvil.  This  connection 
between  heat  and  power  is  shown  in  the  most  perfect  and  masterly  style  by 
Dr.  Tyndall, *  the  industrious  and  worthy  successor  of  Faraday.  He  has 
enriched  this  branch  ot  philosophy  with  a  vast  number  of  practical  demon¬ 
strations  and  experiments,  giving  quite  a  new  and  fresh  appearance  to  a  science 
which  seemed  to  have  reached  its  limits  in  the  stereotyped  repetition  of  descrip¬ 
tions  of  thermometers,  pyrometers,  calorimeters,  and  eternal  disquisitions  on 
specific  heat  and  latent  caloric.  Referring  back  to  heat  as  the  equivalent  for 
power,  there  is  a  telling  experiment  of  Tyndall’s,  in  which  a  brass  tube  con¬ 
taining  water  is  connected  with  a  whirling  table,  and  whilst  it  is  going  round 
with  great  velocity,  it  is  rubbed  with  the  wood  of  a  lemon-squeezer;  the  friction 
soon  generates  enough  heat  to  cause  the  water  to  boil,  and  to  eject  a  cork  with 
which  the  tube  is  closed.  Power  generates  heat,  and  vice  versa.  If  a  mode¬ 
rate-sized  piece  of  lecture-table  apparatus  generating  heat  is  to  be  regarded  as 
a  power,  what  must  be  the  energy  of  the  sun  ?  what  kind  of  force  is  at  work  to 
produce  so  much  heat?  Pouillet  has  carefully  ascertained  the  total  heating 
effect  of  the  sun’s  rays  upon  the  earth,  and  estimating  the  whole  heating 
power  of  the  sun  as  2,300  millions  of  parts,  he  calculates  that  less  than  one 
ot  those  parts  only  reaches  our  earth,  and  yet  it  would  melt  a  layer  of  ice 
thirty-five  yards  thick  over  the  whole  surface  of  our  globe.  This  proportion 
of  heat  is  not  all  available:  some  of  it  is  at  once  converted  into  power  by 
setting  the  air  in  motion,  to  create  the  winds;  another  portion  raises  the  water 
of  the  ocean  into  vapour,  which,  descending  in  the  form  of  rain  on  high  levels, 
such  as  the  mighty  water-shed  which  supplies  the  great  lakes  (discovered  by 
Speke  and  Grant  and  Sir  Samuel  Baker),  the  sources  of  the  Nile,  flows  down 
to  the  lowlands,  giving  rise  to  water  power,  which  is  again  the  equivalent  for 


RotH-re*  ■ind' G ^  1'^ot'on-  By  John  Tyndall,  F.R  S  ,  etc.  Longman,  Green,  Longman, 


THERMOMETRIC  HEAT 


•49 


heat ;  another  part  stimulates  and  increases  the  growth  of  plants ;  and  thus, 
in  ages  long  since  passed  away,  the  heat  of  the  sun’s  rays  was  not  all  lost,  as  the 
older  Stephenson  insisted,  but  stored  up  ready  for  man  to  use  in  another  form, 
viz.,  coal,  and  therefore  called  potential  heat.  The  plants,  being  the  food  of 
animals,  again  contribute  to  the  production  of  animal  heat  and  muscular  force. 
The  sources  of  heat  are  all  connected  with  motion  of  some  kind. 

No.  i.  Friction  is  a  notable  illustration,  and  it  was  by  causing  two  pieces  of 
ice  to  rub  one  against  the  other  that  Sir  Humphrey  Davy  generated  heat, 
liquified  the  ice;  and  like  Dr.  Young,  who  proved  that  light  could  turn  a 
corner,  and  established  by  his  experiments  with  inflection  a  sort  of  basis  upon 
which  the  undulatory  theory  of  light  was  again  reconstructed,  so  this  famous 
experiment  of  Davy  supplied  a  great  fact,  and  gave  the  first  blow  to  the  old 
theory  which  said  that  the  ice  melted  because  latent  heat  was  made  sensible 
heat,  when  it  was  well  known  that  water  at  a  temperature  of  32°  Fahrenheit 
contains  much  more  heat  than  ice  ;  how,  then,  could  the  ice,  already  deficient 
in  heat,  supply  enough  to  satisfy  the  condition  of  water?  There  are  plenty  of 
illustrations  of  the  generation  of  heat  by  friction.  The  flint  and  steel  ;  the 
attrition  of  dried  wood,  as  used  by  savage  tribes  ;  the  famous  experiments  of 
Count  Rumford  whilst  boring  cannon,  when  enough  heat  was  generated  in  two 
hours  and  a  half  to  cause  two  and  a  half  gallons  of  water  to  boil;  the  friction 
of  railway-wheel  axles,  which  have  been  known  to  become  red  hot  and  to  set 
fire  to  the  woodwork  of  the  carriage.  In  North  America,  a  case  is  quoted 
where  heat  was  intentionally  generated  by  waste  water  power  and  used  for 
heating  purposes,  the  generator  being  two  flat  plates  of  iron  which  rubbed 
against  each  other.  Whilst  a  party  of  workmen  were  at  the  bottom  of  a  shaft 
in  Lovel  Mine,  near  Helston,  Plymouth,  the  rope  of  the  cage  or  kibble  caught 
fire  through  friction,  and,  after  gradually  burning  through,  the  cage  tell  a  great 
depth.  Some  of  the  men  saw  the  cage  dropping  and  jumped  away,  but  two 
of  them  were  caught  by  the  falling  mass  and  crushed  to  death. 

No.  2.  Percussion. —  It  was  said  formerly  that  metals  when  struck  with  a 
hammer,  or  with  a  die  in  the  coining-press,  became  hot  because  their  density 
was  increased,  and  therefore  their  capacity  or  containing  power  for  heat  was 
altered  ;  but  it  is  clearly  shown  that  this  is  not  the  true  explanation.  Lead, 
for  instance,  which  becomes  hot  by  percussion,  does  not  increase  in  density, 
and  yet  becomes  hot— so  hot  that  when  projected' from  the  steam  gun  in  the 
form  of  bullets  against  a  wrought-iron  target,  a  flash  of  light  is  apparent  in  a 
darkened  room.  The  heavy  shot  used  for  battering  iron  plates  always  become 
very  hot  after  they  have  struck  the  plate. 

No.  3.  Chemical  Action. — The  bringing  together  of  a  number  of  atoms, 
however  small,  the  clashing  together  (as  Tyndall  calls  it)  of  particles  to  pro¬ 
duce  new  compounds,  as  in  the  heating  and  combustion  of  finely-powdered 
antimony  when  it  is  brought  in  contact  with  chlorine  gas,  or  the  heat  gene¬ 
rated  by  combustion  or  from  other  chemical  changes,  are  all  to  be  regarded  as 
the  result  of  motion  which  the  eye  cannot  detect,  but  which  must  occur  belore 
the  elements  come  in  contact,  combine,  and  form  new  compounds.  I  here  are 
many  chemical  changes  accelerated  by  motion,  and  hence  the  stirring-iod  is 
an  important  mechanical  means  to  secure  the  more  rapid  union  ot  particles. 

•  No.  4  Electrical  Action  — The  very  essence  of  the  existence  of  electrical 
power  is  circulation  or  motion.  The  intense  heat  generated  by  the  discharge 
of  a  powerful  Leyden  battery  through  a  thin  iron  wire  seems  to  be  increased 
by  the  resistance  offered  to  the  passage  of  the  current,  and  thus  work  is  con¬ 
sumed.  The  ignition  of  a  platinum  wire  by  a  current  of  voltaic  electricity 


HEAT. 


J5° 


affords  a  further  instance  of  resistance  ;  whilst  another  wire  of  the  same  size 
made  of  silver,  offering  less  resistance  and  consuming  less  work,  does  not 
become  red  hot.  We  speak  of  a  current  of  electricity:  a  current  is  something 
flowing  ;  it  is  of  course  motion.  Here  again  the  two  forces  are  similarly  con¬ 
vertible.  The  heat  generated  by  the  passage  of  a  current  of  electricity  through 
a  platinum  wire  will  set  up  another  current  of  electricity.  If  the  heat  is  applied 
to  a  series  of  bars  of  bismuth  and  antimony  arranged  properly,  and  thus 
called  a  thermo-battery  or  multiplier — a  thermo-pile  by  which  the  electro¬ 
motive  force  in  the  circuit  is  multiplied— a  most  delicate  indicator  of  heat, 
which  in  connection  with  the  galvanic  needle  is  usefully  and  extensively  em¬ 
ployed  in  experiments  where  heat,  inappreciable  by  a  thermometer  or  other 
ordinary  means,  is  generated.  The  thermometric  current  was  discovered  by 
Seebeck  in  1822.  The  first  thermo-pile  was  constructed  by  (Ersted  and 
Fourier,  and  Nobili  developed  the  power  of  the  thermo-pile  as  a  method  of 
measuring  very  small  changes  of  temperature. 

No.  5.  Vital  Power,  impossible  without  food,  appears  to  be  the  result  of  a 
kind  of  slow  combustion,  or  change  of  carbon  and  hydrogen  into  carbonic 
acid  and  water,  and  furnishes  another  illustration  of  heat  generated  by 
chemical  action.  The  muscular  power  of  a  horse,  as  sagaciously  observed 
by  Count  Rumford,  might  certainly  be  used  to  produce  by  friction  (as  in  the 
boring  of  iron)  enough  heat  to  cause  water  to  boil  for  the  purpose  of  cooking 
victuals,  if  a  quicker  and  more  advantageous  mode  were  not  suggested  by  the 
direct  combustion  of  the  fodder  which  the  horse  must  eat  to  maintain  the 
animal  heat,  in  order  to  be  able  to  exert  his  muscular  energy. 

To  work  out  the  relation  between  heat  and  mechanical  power,  it  has  been 
found  necessary  to  establish  a  standard  of  comparison,  or  unit  of  work,  which 
latter  in  England  is  defined  to  be  “  the  force  required  to  overcome  the  pres¬ 
sure  of  one  pound  through  the  space  of  one  foot.” 

By  a  very  extensive  series  of  experiments  Ur.  J.  P.  Joule  determined  that 
77 2  foot-pounds,  or  units  of  work,  have  to  be  performed  to  raise  a  pound  of 
water  at  about  50°  Fahrenheit  one  degree  ;  772  units  of  work  would,  therefore, 
be  called  the  mechanical  equivalent  of  heat,  and  an  equivalent  to  a  force  that 
would  raise  one  pound  772  feet  high  ;  or,  if  we  reverse  the  statement,  and 
imagine  the  same  water  falling  through  772  feet,  it  would  be  raised  one  degree 
F ahrenheit.  1  he  power  or  force  used  was  measured  by  the  descent  of  weights, 
which  caused  the  apparatus,  viz.,  an  iron  paddle-wheel,  to  rotate  in  water  or 
mercury,  and,  by  the  friction  of  the  iron  and  mercury  or  water,  to  eliminate 
heat,  which  was  estimated  in  the  most  careful  manner.  “Joule’s  equivalent”  is, 
therefore,  a  standard  of  the  most  valuable  and  truthful  kind, verified  by  another 
great  man,  Dr.  Mayer,  who.  by  different  means  and  by  calculation,  makes  out 
the  equivalent  to  be  77 1 '4  foot-pounds,  instead  of  772,  and  thus  proved  how 
correct  had  been  the  previous  experiments  and  calculations  of  Joule. 

Dr.  Young  says,  “  If  heat  is  not  a  substance,  it  must  be  a  quality  ;  and  this 
quality  can  omy  be  motion.  It  was  Newton’s  opinion  that  heat  consists  in  a 
minute  vibratory  motion  of  the  particles  of  bodies,  and  that  this  motion  is 
communicated  through  an  apparent  vacuum  by  the  undulations  of  an  elastic 
medium,  which  is  also  concerned  in  the  phenomena  of  light.  It  is  easy  to 
imagine  that  such  vibrations  maybe  excited  in  the  component  parts  of  bodies  by 
peicussion,  by  friction,  or  by  the  destruction  of  the  equilibrium  of  cohesion  and 
repulsion,  and  by  a  change  of  the  conditions  on  which  it  may  be  restored  in 
consequence  of  combustion  or  of  any  other  chemical  change.”  Further  on,  he 


THERMO  METRIC  HEAT. 


*5* 


says/-  The  effect  of  radiant  heat  in  raising  the  temperature  of  a  body  on  which 
it  falls  resembles  the  sympathetic  agitation  of  a  string,  when  the  sound  of 
another  string,  which  is  in  unison  with  it,  is  transmitted  to  it  through  the  air. 

“All  these  analogies  are  certainly  favourable  to  the  opinion  of  the  vibratory 
nature  of  heat,  which  has  been  sufficiently  sanctioned  bv  the  authority  of  the 
greatest  philosophers  of  past  times  and  of  the  most  sober  reasoners  of  the 
present.  I  hose,  however,  who  look  up  with  unqualified  reverence  to  the 
dogmas  of  the  modern  school  of  chemistry  will  probably  long  retain  a  par¬ 
tiality  for  the  convenient,  but  superficial  and  inaccurate,  modes  of  reasoning 
which  have  been  founded  on  the  favourite  hypothesis  of  the  existence  of  caloric 
as  a  separate  substance ;  but  it  may  be  presumed  that  in  the  end  a  careful  and 
repeated  examination  of  the  facts  which  have  been  adduced  in  confutation 
of  that  system  will  make  a  sufficient  impression  on  the  minds  of  the  cultivators 
of  chemistry  to  induce  them  to  listen  to  a  less  objectionable  theory.” 

These  anticipations  of  Young  have  been  fulfilled  the  re-establishment  of 
the  undulatory  theory  of  light,  by  his  exertions,  has  been  slowly  followed  by 
the  reception  of  the  dynamical  theory  of  heat. 

Thr  Common  Effects  of  Heat. 

When  a  solid  is  raised  in  temperature,  either  by  percussion  or  by  the  direct 
application  of  heat,  the  vibratory  motion  supposed  to  be  set  up  in  the  mole¬ 
cules  or  atoms  of  the  substance  appears  to  overcome  fora  time  their  cohesive 
force,  and  they  are  separated  :  they  occupy  more  space  ;  they  expand,  and,  im¬ 
perceptible  as  that  expansion  must  be  the  eye.  it  may  still  be  made  apparent 
by  a  proper  instrument.  A  miniature  house,  fitted  with  a  number  of  movable 
metallic  tiles,  is  so  ar¬ 
ranged  that,  when  the 
outer  walls  are  driven 
apart  by  any  means, 
the  roof  and  tiles  fall 
in.  Between  the  parts 
of  the  model  represent¬ 
ing  the  walls  of  the 
house  is  arranged  a 
broad  band  of  brass, 
which  is  nicelyadjusted 
by  a  screw,  so  that  it 
just  touches  the  sides,  Fig.  138. 

which  are  held  together  a,  the  spirit-lamp  ;  b,  the  brass  ring  ;  c,  the  brass  ball. 

with  a  spring.  When  a 

series  of  spirit-lamps  are  lighted  under  the  bar,  it  soon  expands  with  great 
force,  and,  overcoming  the  springs  which  hold  the  sides  together,  they  are 
pushed  out,  and  the  rattle  of  the  falling  roof  and  tiles  shows  to  ti  e  e\es  and 
ears  the  catastrophe  that  might  happen  on  a  larger  scale.  1  he  expansion  of 
the  brass  rod  is  thus  indicated  in  a  simple  and  effective  manner.  \\  hen  the 
contents  of  warehouses  provided  with  great  iron  girders  take  fire,  the  latter 
expand,  push  out  the  walls,  and  ultimately  bend  themselves  (when  they  be¬ 
come  red  hot)  with  the  superincumbent  weight  above  them. 

What  is  called  Gavesande’s  ball  (Fig.  138)  is  a  simple  and  effective  mode  of 
showing  cubical  expansion.  A  brass  ball  is  carefully  turned  and  polished, 
so  that  it  exactly  fits,  and  will  pass  through  a  metal  ring  ;  but,  when  heated, 


152 


HEAT. 


expansion  takes  place,  and,  instead  of  falling  through  the  ring,  it  is  held  up  as 
in  a  ring-stand,  and  will  no  longer  pass  through  the  opening. 

The  expansion  of  a  fluid  body  is  also  shown  by  placing  some  coloured  water 

in  a  flask ;  to  this  is  fitted  a  cork  and  tube  with  a 
small  bore,  which  is  bent  round  at  the  top,  so  that 
any  liquid  ejected  by  expansion  may  fall  into  a 
shallow  dish  containing  some  bits  of  potassium; 
the  rise  of  the  liquid  in  the  tube  may  be  watched 
by  placing  a  piece  of  cardboard  behind  it,  and 
directly  the  full  expansion  occurs  the  liquid  is 
ejected  and  the  potassium  takes  fire. 

The  expansion  of  gases  by  heat  is  readily  shown 
by  various  simple  experiments.  The  neck  of  an 
empty  retort  is  placed  under  water,  and  directly 
the  body  is  heated  the  air  expands  and  passes  in 
bubbles  through  the  water;  before  removing  the 
lamp  a  little  ink  should  be  stirred  into  the  water, 
so  that  when  the  heat  is  withdrawn  the  amount 
of  expansion  may  be  shown  by  the  rise  of  the 
coloured  water  to  fill  the  space  at  first  occupied 
with  air,  but  now  lost  by  expansion. 

The  Montgolfier  or  fire-balloon  has  never  ceased 
to  please,  because  its  inflation  is  so  simple  and 
rapid.  The  only  difficulty  seems  to  be  to  avoid 
setting  the  paper  on  fire;  this  is  easily  prevented 
by  using  a  metal  funnel  with  coarse  wire  gauze  at 
the  top,  and  insid-"  of  which  the  large  piece  of  tow, 
wetted  with  spirits  of  wine,  is  allowed  to  burn ;  the 
potassium ;  d,  the  ring-stand  and  inverted  funnel  maybe  supported  on  three  legs, 
spmt-iamp.  and  mouth  should  be  at  least  3  in.  in  diameter, 

in  order  to  allow  the  heated  air  to  pass  rapidly  into 
the  paper  bag.  By  attaching  a  thin  string,  the  balloon  may  be  let  up  and 
down  any  number  of  times.  When  the  balloon  is  intended  for  the  amusement 
of  young  people,  at  an  out-door  fete ,  the  balloon  can  be  sheltered  from  the 
wind  by  a  blanket  stretched  between  two  poles ;  and  if  the  balloon,  when 
nearly  ready  to  start,  is  blown  by  a  sudden  gust  of  wind  across  the  heating 
apparatus,  it  does  not  catch  fire,  because  it  is  protected  from  the  flame  by  the 
funnel  and  wire  gauze. 

This  mode  of  sending  up  a  fire-balloon  is  the  safest,  because  it  does  not  carry 
any  fire.  The  late  accidental  and  total  destruction  by  fire  of  the  immense  fire- 
balloon  in  the  grounds  of  the  Crystal  Palace  sufficiently  indicates  the  danger 
of  these  aeronautical  machines,  and  how  soon  they  may  ignite;  indeed,  no 
Montgolfier  balloon  on  the  large  scale  should  be  used  on  this  principle  without 
first  rendering  the  material  of  which  it  is  composed  incapable  of  combustion, 
by  preparing  it  with  a  solution  of  phosphate  of  ammonia. 

Robertson,  in  his  “  Recreative  Memoirs,”  gives  a  very  interesting  account  of 
the  construction  and  ascent  of  an  enormous  Montgolfier  or  fire  balloon  at 
Vienna,  in  the  year  1781.  It  was  the  first  experiment  of  the  kind  tried  there, 
and  was  carried  out  in  a  most  fearless,  not  to  say  reckless,  manner  by  Gaspard 
Stuver.  The  length  of  the  balloon  (Fig.  1 4 1 ),  which  was  constructed  like  a 
cylinder  closed  at  both  ends  with  cones,  amounted  to  60  ft.  It  was  made  of 


Fig.  139. 

a,  the  flask  with  cork  and  tube, 
tilled  with  water  coloured  with 
ink  or  solution  ot  indigo  to  the 
point  b:  c.  cud  containing  the 


THERMOMETRIC  HEAT 


i53 


Fig.  140. — The  Paper  Montgolfier. 

The  sheet-iron  funnel,  with  coarse  wire  gauze  at  the  end,  supported  on  three  legs  about  1  ft.  from 
ground.  An  iron  ladle  containing  tow  moistened  with  spirits  of  wine,  or  a  small  tire  fed  with 
sha\  ings,  will  do. 


canvas  lined  with  sized  paper.  Three  persons  ascended  with  Stuver  in  a 
Danube  boat  arranged  as  a  car,  and  attached  to  the  balloon  by  proper  cords. 
They  entered  the  car  with  the  greater  courage  because  they  did  not  intend  to 


Fig.  1 41. 


allow  the  balloon  to  travel  where  the  winds  might  direct  it,  but  to  retain  it  as 
a  “  captive  balloon  ”  (like  the  one  at  the  Crystal  Palace)  by  a  strong  cord  ; 
but,  unfortunately,  the  rope  was  not  strong  enough:  it  broke,  and  away  went 
the  balloon  with  immense  rapidity,  not  without  considerable  pen  to  ie 
unfortunate  passengers.  The  shock  was  so  violent  that  the  boat  ti  teci  on 


*54 


HEAT. 


one  side,  and  the  fire  was  thrown  out  on  the  canvas.  By  a  happy  forethought, 
the  men  were  provided  with  water  and  long  rods  to  which  were  attached  large 
sponges,  and  with  these  they  courageously  stopped  the  further  progress  of 
the  flames.  The  voyage  was  not  very  long:  the  unwieldly  machine  descended 
a  little,  and  knocked  down  a  large  wooden  framework  prepared  for  some 
pyrotechnic  display :  it  then  reascended,  grazed  the  tops  of  the  trees  in  the 
Prater  or  park,  and  fell  on  the  grass  on  the  other  side  of  the  Danube. 

Amount  of  Expansion  in  Solids,  Liquids,  and  Gases. 

MEASURES  OF  HEAT — THERMOMETRY. 

The  fact  that  the  particles  or  molecules  of  a  solid  body  are  pushed  away 
from  each  other  by  heat,  and  suffer  a  certain  increase  in  dimension,  called 
expansion,  has  been  already  mentioned,  and  in  every-day  life  examples  are  not 
wanting.  The  moulds  for  casting  in  metal  are  always  made  larger  than  the 
size  required,  in  order  to  allow  for  the  expansion  of  the  metal  when  in  the 
liquid  state.  The  iron  hoops  of  carriage  or  cart  wheels  are  put  on  red  hot, 
and  being  cooled  suddenly  by  the  application  of  cold  water,  they  contract 
with  great  force  and  draw  all  parts  of  the  wheel  firmly  together.  In  bottles 
the  stopper  is  often  fixed  tight,  and  cannot  be  removed  by  any  force  that  is 
applied  ;  when  this  is  the  case,  the  outer  part  of  the  neck  should  be  carefully 
heated  over  the  flame  of  a  spirit-lamp  ;  expansion  takes  place,  and  then  the 
neck  is  tightly  grasped  with  the  hand,  protected  by  a  duster  in  case  of 


Fig.  142. 

a  b,  cast-iron  frame;  c  c,  red-hot  iron  bar,  passed  through  the  holes  in  a  b,  and  fitted  tight  by  the 
screw  d  e  represents  the  same  iron  frame  broken  by  the  contraction  of  the  bar. 


accidental  breakage ;  a  slight  effort,  and  particularly  moving  the  stopper 
backwards  and  forwards  in  one  direction  only,  and  carefully  avoiding  a  motion 
which  would  cause  the  stopper  to  turn  round,  will  soon  be  rewarded  by  the 
extrication  of  t  le  stopper  from  the  tight  embrace  of.  the  neck  of  the  bottle.  A 
piece  of  iron,  cast  with  two  elbow-pieces,  each  bored  so  as  to  allow  an  iron 
bar  to  be  placed  through  them  when  red  hot,  and  then  screwed  up  with  a 
thumb-screw  as  tight  as  possible,  instantly  breaks  off  one  or  both  the  elbow- 
pieces  when  the  red-hot  bar  is  cooled  by  being  suddenly  plunged  into  water. 

The  amount  of  expansion,  or  coefficient  of  expansion,  of  solids  is,  however, 
exceedingly  small,  and  requires  the  utmost  nicety  of  experiment  to  discover 
ics  amount.  I  he  difference  between  linear  expansion,  or  the  increase  of 
length,  and  superficial  expansion,  or  the  increase  in  the  area  of  a  surface, 
must  of  course  be  remembered. 


THE  EXPANSION  OF  SOLIDS. 


*55 


The  unequal  expansion  of  metals  is  shown  by  riveting  together  two  flat 
plates  of  iron  and  brass;  the  latter,  expanding  in  a  greater  degree  than  the 
former,  causes  the  compound  bar  to  take  the  form  of  an  arch  or  curve  when 
heated  ;  the  brass  side  being  uppermost,  the  arch  ascends,  and  a  convex  figure 
is  observed  ;  but  if  downwards,  the  reverse  or  concave  form  is  produced. 
The  rise  or  arching  of  the  riveted  bars  is  easily  shown  if  united  with  an 
electrical  battery  ringing  a  bell  with  which  contact  only  is  made  when 
the  curve  is  produced.  Attention  is  further  directed  to  the  result  of  un¬ 
equal  expansion  when  the  spirit-lamp  is  withdrawn  and  the  bar  cooled 
with  ice  or  cold  water ;  the  bell  ceases  to  ring,  and  the  bar  again  becomes 
straight. 

It  is  on  this 
principle  that 
Breguet  con¬ 
structs  his 
most  delicate 
metallic  ther¬ 
mometers.  The 
solid  affected 
by  heat  con¬ 
sists  of  a  thin 
metallic  rib¬ 
bon,  -ompesed 
of  three  strips 
of  platinum, 
gold,  and 
silver,  passed 
through  a 
rolling-mill  to¬ 
gether.  The 
ribbon  is  then 
roiled  in  the 

form  of  a  helix,  the  silver  side  being  outermost.  As  the  temperature  rises  the 
silver  expands  more  than  the  gold,  and  the  gold  more  than  the  platinum  ;  one 
end  is  fixed  to  a  proper  support,  and  the  other  is  attached  to  a  copper  needle. 

The  sniral  unwinds  when  the  heat  increases,  and  the  contrary  result 
occurs  if  heat  is  withdrawn,  and  it  cools.  The  needle  moves  round  a  scale 
which  is  graduated  by  direct  comparison  with  a  standard  mercurial  thermo¬ 
meter. 

The  following  table  shows  the  comparative  increase  of  length  or  linear 
expansion  in  bars  or  rods  of  various  substances  when  they  are  heated,  from 
the  freezing  to  the  boiling-point  of  water — viz.,  from  320  to  212°  Fahrenheit, 
according  to  the  authority  of  Graham: 


Fig.  143- 

A  a,  ihe  compound  bar  of  brass  and  iron,  heated  by  a  spirit-lamp,  and  rising  in 
a  curve  towards  the  wire  n,  connected  with  the  bell  c  and  battery  d,  of  which  the 
other  wire  is  attached  to  the  compound  bar  at  e.  When  the  spirit-lamp  is  removed, 
the  bar  contracts,  and  the  contact  is  broken  at  u. 


Zinc  (cast)  . 

» 

1  on  323 

Zinc  (sheet) . 

* 

»  >,  340 

Lead  . 

. 

»  »  351 

Tin 

1  „  516 

Silver  . 

«  „  524 

Copper 

• 

1  „  581 

Brass  . 

• 

1  „  584 

Pure  gold  . 

1 

on  682 

Iron  wire  . 

I 

»  812 

Palladium  . 

1 

„  1,000 

Glass  without  lead  . 

1 

„  1,142 

Platinum  . 

1 

„  1,167 

Flint  glass 

1 

„  1,248 

Black  marble  . 

1 

,,  2,833 

HEAT. 


T56 


In  this  table  it  will  be  noticed  that  glass  and  platinum  elongate  nearly  the 
same,  and  this  fact  explains  why  platinum  wire  can  be  melted  into  glass  tubes 
made  of  glass  not  containing  lead,  such  as  the  hard  German  glass,  without 
causing  the  tubes  to  crack,  either  by  expansion  or  contraction,  at  the  points 
where  the  wires  are  inserted.  The  minute  linear  expansion  of  black  marble, 
only  one  on  2,833,  is  of  course  the  reason  why  it  is  used  as  the  pendulum-rod 
in  the  clock  of  the  Royal  Society  of  Edinburgh. 

Even  a  bar  or  rod  of  ice  elongates  by  an  increase  of  temperature,  and  is 
found  even  to  surpass  zinc  ;  the  ice  will  elongate  1  part  on  267,  the  zinc  1  on 
323  parts.  Ice  will  also  contract  when  exposed  to  a  temperature  lower  than 
its  freezing-point,  and  the  amount  of  contraction  has  been  carefully  observed 
up  to  30°  or  40°  below  the  freezing-point  of  water. 

A  solid  may  expand  at  a  uniform  rate  up  to  a  certain  point,  and  then,  if  the 
heat  is  increased,  the  elongation  becomes  more  rapid. 

Amongst  metals,  platinum  is  found  to  expand  with  the  greatest  uniformity, 
most  probably  in  consequence  of  its  great  infusibility. 

Certain  crystals  of  the  same  nature  throughout  expand  very  unequally  in 
their  several  dimensions  of  length,  and  breadth,  and  height,  and  they  are 
found  to  elongate  in  a  greater  degree  in  the  direction  of  one  axis  than  in 
another.  Iceland  spar  possesses  this  property  ;  and  was  found,  by  Professor 
Mitscherlich,  to  expand  in  one  direction,  the  crystallographic  axis,  and  to 
contract  in  the  other  at  right  angles  to  the  former,  so  that  the  anomaly  of 
expansion  and  contraction  in  one  body  was  apparent.  Another  remarkable 
anomaly  of  the  same  kind  will  be  noticed  presently  in  connection  with  a  fluid 
— viz.,  water — when  reduced  to  a  certain  temperature.  The  difference  between 
linear,  surface,  and  volume  expansion  is  determined  by  the  geometrical  prin¬ 
ciple,  that  when  a  solid  increases  in  magnitude  without  undergoing  a  change 
in  figure,  taking  the  linear  expansion  as  the  unit,  or  say  100,  the  superficial 
expansion  will  be  twice  the  linear,  100x2  =  200,  and  cubic  expansion  three 
times  the  linear,  100x3  =  300. 

Thus  the  linear  coefficient  of  expansion  of  glass  being  o-ooo,oo8,  the  cubic 
expansion  of  the  same  will  be  o-ooo,o24;  the  dilatation  of  volume  and  surface 
of  solids  being  calculated  from  linear  expansion. 

- ♦ — — 

THE  EXPANSION  OF  LIQUIDS. 

It  has  already  been  noticed  that  the  expansion  of  solids  by  heat  is  so  con¬ 
trolled  by  the  antagonistic  force  of  cohesion,  that  it  is  not  perceptible  to  the 
vision  without  the  use  of  secondary  means,  such  as  those  described  at  page  127. 

With  liquids  the  amount  of  expansion  is  very  perceptible  when  they  are 
inclosed  in  narrow  glass  tubes,  and  in  fact  is  much  greater  than  that  of  solids, 
because  the  force  of  cohesion  is  diminished  so  much  that  every  particle  is 
free  to  move  upon  its  neighbouring  particles.  Some  fluids  expand  more  than 
others.  Alcohol  is  more  expansible  than  water,  and  water  more  than  mercury ; 
in  fact,  alcohol  expands  six  times  more  than  mercury.  Messrs.  Dulong 
and  Petit  employed  the  most  refined  means  to  ascertain  the  rate  of,  and 
absolute  expansion  of,  mercury,  and  they  found  that  the  coefficient  of  the 
latter  was  1-5550  between  the  freezing  and  boiling  point  of  water,  the  rate 
being  as  follows : 


THE  EXPANSION  OF  LIQUIDS. 


x57 


From  o°  to  ioo’ Centigrade,  mercury  expands  i  measure,  or  55^ 

„  ioo°  to  200°  „  „  „  1  „  54j 

„  200°  to  300’  „  „  „  1  53 

Liquid  carbonic  acid  expands  four  times  more  than  air,  and,  when  heated 
from  32°  to  86  Fahrenheit,  ioo  measures  expand  to  140. 

There  are  other  fluids,  such  as  liquid  sulphurous  acid,  hyponitrous  acid, 
cyanogen,  and  the  chloride  of  ethyle,  which  also  expand  very  considerably 
when  heated. 

Alcohol  and  bisulphide  of  carbon  expand  uniformly,  which  is  another 
curious  fact,  because  their  boiling-points  are  so  different,  the  former— alcohol 
— being  1730,  the  latter  1 16". 

Liquids,  as  a  rule,  expand  by  heat,  and  contract  by  cold. 

There  is,  however,  a  remarkable  exception,  probably  more  apparent  than  real 
when  the  theory  of  the  expansion  of  liquid  is  better  understood,  that  water 
which  becomes  solid  in  all  parts  of  the  globe  at  the  level  of  the  sea  at  32 
Fahrenheit,  or  of  oJ  Centigrade,  expands  instead  of  contracting  when  the  water 
reaches  a  temperature  of  40’  Fahrenheit,  and  falls  to  320 :  the  amount  of  expan¬ 
sion  is  not  very  great,  being  one  part  in  ten  thousand  at  320. 

But  the  fact,  which  at  first  was  thought  illusory,  is  indisputable,  as  proved 
by  the  experiments  of  Dr.  Hope.  He  placed  two 
thermometers  in  a  large  vessel  of  water,  the  one  being 
at  the  top,  and  the  other  at  the  bottom.  Up  to  a 
temperature  of  40°,  the  cold  water  contracted,  and, 
being  the  heavier,  sank  to  the  bottom,  and  the  lower 
thermometer  registered  the  greatest  cold.  After  40° 
was  passed,  the  water  evidently  expanded;  the  coldest 
water  was  found  to  be  at  the  top,  and  duly  recorded 
by  the  thermometer  sinking  to  32  ,  whilst  the  warmer 
water,  which  ought,  according  to  the  law  of  expansion, 
to  have  been  uppermost,  remains  at  the  bottom,  and 
therefore  was  heavier,  bulk  for  bulk,  than  the  water 
about  to  crystallize.  It  is  this  remarkable  exception 
that  preserves  the  fish  in  the  lakes  and  rivers.  During 
the  severe  winters  of  Siberia  the  water  is  frozen  many 
feet  thick;  but  it  is  related  by  one  of  the  exiles  in  this 
roomy  but  severe  prison,  that  part  of  their  amusement 
in  certain  seasons  consisted  in  fishing  in  great  holes 
in  the  ice,  and  all  they  caught  they  partially  but  imme¬ 
diately  ate  raw  and  living,  biting  out  a  piece  of  the 
back,  which  was  declared  to  be  a  most  agreeable  tit¬ 
bit. 

It  is  evident  that  the  fish,  if  frozen,  could  have  no 
power  of  locomotion— they  must  die;  so  that  on  the 
arrival  of  winter  the  Siberian  waters  would  throw  up 
their  dead  fish,  as  all  would  be  killed  if  the  water,  which  is  a  very  bad  con¬ 
ductor  of  heat,  did  not  remain  at  40°  at  the  bottom  of  the  lakes,  rivers,  and 
seas. 

Bismuth  is  said  to  possess  the  same  curious  property  of  expanding  whilst 
it  is  being  cooled,  and  thus  iron  bottles  filled  with  melted  bismuth,  and  plugged 
with  a  screw,  burst  at  the  moment  the  metal  assumes  the  solid  state.  A 
bomb-shell  or  cast-iron  bottle  filled  with  water,  and  screwed  up,  bursts  in  the 


Fig.  144. 

Dr.  Hope's  experiment. 


HEAT 


158 


same  manner  if  surrounded  with  a  freezing  mixture  of  pounded  ice,  or  snow 
and  salt.  With  respect  to  bismuth  it  is  right  to  state  that  Professor  Tyndall's 
conclusion  on  this  similarity,  stated  in  his  work  on  “  Heat  as  a  Mode  of 
Motion,”  in  which  it  is  asserted  “that  the  anomalous  expansion  of  water  in 
the  act  of  cooling  below  40°  Fahrenheit  is  by  no  means  an  isolated  instance  of 
the  kind,  but  that  other  bodies,  and  particularly  melted  bismuth,  participates 
in  this  extraordinary  property  of  expanding  near  the  point  of  solidification,” 
is  opposed  by  Mr.  Alfred  Tribe,  who,  after  making  experiments  upon  this 


Fig.  145. — Siberian  Exiles  fishing. 


subject,  considers  that  the  analogy  between  water  and  bismuth  is  imperfect, 
since  in  the  case  of  the  molten  metal  there  is  no  perceptible  range  of  tem¬ 
perature  through  which  it  expands  on  cooling.  The  act  of  solidification  is 
itself  accompanied  by  an  increase  in  bulk ;  but  there  is  no  evidence  of  this 
expansion  taking  place  prior  to  the  act  of  crystallization.  When  the  crystal¬ 
lization  of  any  salt  is  exhibited  on  the  disc  with  the  oxy-hydrogen  microscope, 
the  visible  illustration  of  the  motion  of  the  particles  is  very  decided,  as  the 
crystals  shoot  out  and  interlace  with  each  other.  The  act  of  solidification  is, 
therefore,  one  of  motion,  and  heat  is  produced,  and  very  decidedly  so  in  the 
case  of  sulphate  of  soda  or  glauber  salt.  A  large  flask  filled  with  a  satu¬ 
rated  solution  of  sulphate  of  soda,  and  carefully  closed  with  a  cork  and 
bladder,  so  that  the  air  is  excluded,  does  not  solidify  when  cold.  Crystalliza¬ 
tion  only  begins  when  the  air  is  admitted;  the  solution  of  a  minute  volume  of 
air  liberates  a  tiny  crystal,  and,  the  nucleus  once  formed,  cohesion  sets  in  with 
rapidity ;  the  molecules  arc  set  in  motion,  and  sufficient  heat  is  produced  to 
be  felt  by  the  hand,  and  becomes  still  more  apparent  if  a  delicate  air-ther¬ 
mometer  is  used.  India-rubber  caoutchouc,  when  stretched  and  apparently 
expanded,  becomes  warm  instead  of  cold;  is  it  possible  to  suppose  that  the 
expansion  in  the  direction  of  the  length  may  cause  contraction  in  the  trans¬ 
verse  direction  in  the  breadth,  and  the  sum  of  this  violent  motion  is  in  favour 
of  the  contraction,  and  thus  heat  is  the  result? 

I  he  contraction  of  stretched  or  expanded  caoutchouc  by  heat  is  another 


THE  THERMOMETER. 


1 59 


remarkable  anomaly.  It  was  suggested  by  Mr.  Thompson  that  it  might 
shorten  if  heated,  and  the  fact  was  proved  by  Tyndall,  who  first  stretched  a 
vulcanized  india-rubber  tube  by  a  ten-pound  weight,  and  surrounding  it  with 
hot  air,  the  caoutchouc  tube  contracted  and  lifted  the  weight.  In  this  case, 
motion,  the  stretching  of  the  caoutchouc,  eliminates  heat,  which  again  pro¬ 
duces  motion  when  the  stretched  caoutchouc  is  warmed  and  lifts  the  weight 
by  the  contraction  of  its  substance. 

The  expansion  of  fluids  by  heat,  and  the  reverse,  is  taken  advantage  of  in 
the  construction  of  those  useful  instruments  called  thermometers,  or  heat- 
measurers,  and  first  invented  by  Galileo  before  1597. 

A  glass  tube  with  a  small  bore,  sufficiently  so  to  be  capillary,  is  selected 
with  care,  in  order  to  secure  the  same  diameter  throughout.  The  bores  of 
some  tubes  are  like  an  elongated  cone,  and,  if  they 
were  used,  the  mercury  would  expand  much  more  in 
some  parts  of  the  tube  than  in  others,  and  hence  the 
indications  of  such  a  thermometer  would  be  incorrect. 

A  little  mercury,  amounting  to  an  inch  in  length,  is 
allowed  to  enter  the  tube,  and  being  moved  from  one 
end  of  the  tube  to  the  other,  it  is  soon  discovered 
whether  the  mercury  increases  or  decreases  in  length, 
or  remains,  as  is  usually  the  case,  of  the  same  linear 
dimensions  in  all  parts.  The  proper  length  having 
been  cut  off,  one  end  is  melted  and  blown  out  into  a 
bulb,  the  other  being  formed  into  a  cup  or  funnel- 
shape  form,  to  hold  the  mercury,  which  is  forced  in; 
the  tube  is  now  inclined  slightly,  and  the  air  in  the 
bulb  expanded  by  heat;  it  is  afterwards  allowed  to 
cool,  and,  as  the  air  cools  and  contracts,  the  mercury 
from  the  upper  funnel  is  forced  in  by  the  pressure  of 
the  air,  and  enters  to  supply  the  place  of  the  air  driven 
out  by  expansion.  To  get  rid  of  the  rest  of  the  air, 
the  mercury  is  alternately  boiled  and  cooled  until  the 
bulb  and  part  of  the  tube  are  full  of  mercury. 

Having  thus  filled  the  bulb  and  one-third  of  the 
tube,  the  next  steo  is  to  seal  it  hermetically,  which  is 
done  by  heating  the  mercury  to  the  boiling-point,  and 
at  the  moment  the  mercury  is  overflowing  at  the 
summit  the  glass  is  fused  with  a  flame,  urged  by  a  blow¬ 
pipe  (Fig.  147),  before  the  mercury  has  had  time  to 
contract;  and  if  this  operation  has  been  skilfully  per¬ 
formed,  a  perfectly  void  space,  or  vacuum,  free  from 
air,  is  obtained  as  tne  mercury  sinks  or  contracts  in  the  bulb  and  tube. 

The  instrument  in  its  present  state  will  show  an  increase  or  decrease  of 
heat  by  the  rising  or  falling  of  the  mercury;  but  such  indications  would  be 
described.  The  graduation  of  the  instrument  is,  therefore,  of  paramount  im¬ 
portance,  and  standard-points  must  be  obtained — such,  that  they  shall  be  the 
same  in  every  thermometer,  whatever  may  be  the  scale. 

Sir  Isaac  Newton  enjoys  the  merit  of  having  selected,  in  the  year  I7°b  the 
temperature  of  ice,  which  is  dissolving  and  liquifying,  for  one  point,  and  boiling 


HEAT. 


1 60 


water,  emitting  steam  freely  and  without  pressure,  for  the  other.  Ice  always 
melts  at  the  same  temperature,  and  pure  water  invariably  boils  at  the  same 
temperature,  when  the  barometer  stands  at  29  8  in. 

It  is  only  necessary  to  immerse  the  thermometer  alternately  in  melting  ice 
and  in  boiling  water,  with  certain  precautions,  anti  to  mark  the  point  at  which 
the  mercurial  column  stands— one  being  called  the  freezing-point,  and  the 
other  the  boiling-point. 

The  instrument  must  be  immersed  in  the  melting  ice  until  the  mercury 
becomes  perfectly  stationary.  The  immersion  in  boiling  water  requires  the 
greatest  care,  and  a  time  should  be  selected  when  the  barometer  stands  at 
29  8  or  30  in.  The  depth  of  the  water  in  the  vessel  should  not  exceed  2  in. 


Fig.  147. — Blow-pipe  work  in  Negreiti  and  Zambrcfs  Thermometer  Room. 

The  vessel  must  not  be  a  shallow  one,  but  sufficiently  deep  to  contain  the 
bulb  and  nearly  all  that  part  of  the  tube  up  which  the  mercury  will  rise  when 
placed  in  boiling  water.  Distilled  water  should  be  used,  and  brisk  ebullition 
maintained,  and  the  steam  allowed  to  escape  freely,  as  any  confinement  of  it 
would  raise  the  temperature  above  that  of  boiling  -water.  The  space  or 
interval  between  the  two  points  is  now  divided  into  any  number  of  equal 
parts,  which  vary  according  to  the  scale  used  (Fig.  148.)  This  great  step  in 
the  improvement  of  thermometers  was  first  made  by  Fahrenheit  of  Dantzic 
about  1714. 

In  England,  the  interval  according  to  Fahrenheit  is  divided  into  180  parts, 
the  zero  being  320  below  the  freezing-point.  On  the  Continent,  the  interval  is 
divided  by  Ce'sius  into  100  parts,  and  is  called  the  Centigrade  scale. — the  zero 
commences  with  the  freezing-point ;  sometimes  into  80  parts,  called  Reau- 
mer’s  scale,  the  zero,  as  before,  being  the  freezing-point  of  water.  Of  the 
three,  that  of  Celsius  of  Upsala  is  the  most  simple,  and  will  be  gradually 
adopted  throughout  the  civilized  world. 


THE  THERMOMETER. 


16 1 


Fig.  148. — Graduation,  by  a  Machine ,  of  the  Tubes  after  the  freezing  and 
boiling  points  have  been  determined. 


These  scales  are  easily  reduced  from  one  to  another  by  ascertaining  their 
numerical  relation. 

Thus  180  is  to  100  as  9  to  5  ; 

1 80  ,,  80  j,  9  n  4- 

Fahrenheit’s  is,  therefore,  reduced  to  the  Centigrade  scale  by  multiplying  by 
5  and  dividing  by  9;  or  to  that  of  Reaumer  by  multiplying  by  4  and  dividing 

by  9- 

The  Celsius  or  Centigrade  and  Rcaumcr’s  scales  are  reduced  to  Fahrenheit’s 
scale  by  reversing  the  process :  the  multiplier  in  both  cases  being  9,  the  divisor 
will  be  5  with  Centigrade  and  4  with  Reaumer. 

The  reduction  is,  however,  a  little  complicated  when  it  is  remembered  that 
Fahrenheit’s  zero  is  32 °  below  the  freezing-point  of  water,  so  that  in  all  these 
calculations  32  must  be  first  subtracted  when  Fahrenheit  is  reduced  to  Centi¬ 
grade  or  Reaumer,  and  added  when  the  contrary  is  required. 

1st  Example.  To  reduce  2120  Fahrenheit  to  Centigrade:  2123 — 32’=iSo°x 
5  =900-4-9=  ioo°  C. 

2nd  Example.  To  reduce  ioo°  Centigrade  to  Fahrenheit:  100X9=900-4- 
5  =  1 8o°-f  32°= 2 1 20  F. 

The  freezing-point  of  water  is  therefore  designated  and  known  in  all  books 
by  the  following  expressions:  o°C.,  o°  R.,  320  F. 

The  boiling-point  of  water,  by  too°C.,  8o°  R.,  1 120  f. ;  C.  being  Centigrade, 
R.  R<5aumer,  and  F.  Fahrenheit. 

The  limits  to  the  use  of  the  mercurial  thermometer  are  the  points  at  which 
the  metal  solidifies,  or  is  frozen,  viz.,  at  390  below  zero  F.,  or  at  which  the 
metal  boils,  662°  F.,  or  450°  above  the  boiling-point  of  water;  hence  in  the 
one  case  degrees  of  extreme  cold  are  registered  by  thermometers  filled  with 

11 


162 


HEAT. 


alcohol,  which  has  never  been  known  to  freeze  at  the  greatest  known  cold ; 
and,  in  the  other  case,  all  temperatures  above  662°  may  be  registered,  to  a 
certain  point,  by  the  air-thermometer;  but  all  temperatures  which  soften  glass 
and  go  beyond  that  point  can  be  estimated  only  by  the  pyrometer.  The  air- 
thermometer  will  be  explained  in  treating  of  the  expansion  of  gases ;  and  in 
ending  the  description  of  the  ordinary  mercurial  thermometer,  it  may  be 
stated  that  the  bulbs  are  liable  to  a  permanent  change  of  capacity,  which 
displaces  the  zero ;  hence  it  is  usual  to  keep  standard  thermometers  three 
or  four  years  before  they  are  graduated. 

Thermometers  are  constructed  for  a  variety  of  purposes,  and  have,  there¬ 
fore,  different  names  given  to  them.  In  illustration  of  this  statement,  we  give 
a  drawing  of  Negretti  and  Zambra’s  maximum  thermometer  for  registering 
the  highest  daily  temperature  of  the  air,  or  degree  of  heat  at  any  particular 
hour  of  the  day — 


the  construction  of  which  is  as  follows : — A  small  piece  of  glass  is  inserted 
in  the  bend  near  the  bulb,  and  within  the  tube,  which  it  nearly  fills:  at  an 
increase  of  temperature,  the  mercury  passes  this  piece  of  glass ;  but  on  a 
decrease  of  heat,  not  being  able  to  recede,  it  remains  in  the  tube,  and  thus 
indicates  the  maximum  temperature.  After  reading,  it  is  easily  adjusted. 
Hitherto  every  series  of  meteorological  observations  has  been  more  or  less 
broken  by  the  frequent  plunging  of  the  steel  index  into  the  mercury,  or  be¬ 
coming  otherwise  deranged.  Messrs.  Negretti  and  Zambra  have,  in  their 
maximum  thermometer,  supplied  a  want  long  felt. 


consists  of  a  glass  tube,  the  bulb  and  part  of  the  bore  of  which  is  filled 
with  perfectly  pure  spirits  of  wine,  in  which  floats  freely  a  black  glass  index.  A 
slight  elevation  of  the  thermometer,  bulb  uppermost,  will  cause  the  glass  index 
to  flow  to  the  surface  of  the  liquid,  where  it  will  remain,  unless  violently 
shaken.  On  a  decrease  of  temperature,  the  alcohol  recedes,  taking  with  it  the 
glass  index ;  on  an  increase  of  temperature,  the  alcohol  alone  ascends  in  the 
tube,  leaving  the  end  of  the  index  furthest  from  the  bulb  indicating  the 
minimum  temperature. 


THE  PYROMETER. 


163 


Directions  for  using  the  Minimum  Thermometer  for  determination  of  the 
Minimum  Temperature  of  the  Air.— Having  caused  the  glass  index  to  flow  to 
the  end  of  the  column  of  spirits,  by  slightly  tilting  the  thermometer  bulb  upper¬ 
most,  suspend  the  instrument  in  the  shade,  with  the  air  passing  freely  to  it  on 
all  sides,  by  the  two  brass  plates  attached  for  that  purpose,  in  such  manner 
that  the  bulb  is  about  half  an  inch  lower  than  the  upper,  or  the  end  of  the 
thermometer  furthest  from  the  bulb, — then,  on  a  decrease  of  temperature,  the 
spirits  of  wine  will  descend,  carrying  with  it  the  glass  index  ;  on  an  increase  of 
temperature,  however,  the  spirits  of  wine  will  ascend  in  the  tube,  leaving  that 
end  of  the  small  glass  index  furthest  from  the  bulb  indicating  the  minimum 
temperature.  To  re-set  the  instrument,  simply  raise  the  bulb  end  of  the  ther¬ 
mometer  a  little,  as  before  observed,  and  the  index  will  again  descend  to  the 
end  of  the  column,  ready  for  future  observation.  The  same  instrument  may 
be  used  as  a  terrestrial  radiation  thermometer,  and  when  in  use  is  to  be  placed 
with  its  bulb  fully  exposed  to  the  sky,  resting  on  grass,  with  its  stem  supported 
by  little  forks  of  wood. 

By  no  means  jerk  or  shake  an  alcohol  minimum  thermometer  when  re  setting 
it,  for  by  so  doing  it  is  liable  to  disarrange  the  instrument,  either  by  causing  the 
index  to  leave  the  spirit,  or  by  separating  a  portion  of  the  spirit  from  the 

main  column. 

As  alcohol  thermometers  have  a  tendency  to  read  lower  by  age,  owing  to 
the  volatile  nature  of  the  alcohol  allowing  particles  in  the  form  of  vapour  to 
rise  and  lodge  in  the  tube,  it  becomes  necessary  to  compare  them  occasionally 
with  a  mercurial  thermometer  whose  index  error  is  known ;  and  if  the  differ¬ 
ence  be  more  than  a  few  tenths  of  a  degree,  examine  well  the  upper  part  of 
the  tube  to  see  if  any  alcohol  is  hanging  in  the  bore  thereof ;  if  so,  the  detached 
portion  of  it  can  be  joined  to  the  main  column  by  swinging  the  thermometer 
with  a  pendulous  motion,  bulb  downwards. 

Professor  fait  remarks  that  amongst  the  more  novel  applications  of  electri¬ 
city  is  that  most  philosophical  application  of  “electric  resistance  in  metals 
when  they  are  heated,”  by  Mr.  Siemens,  in  the  construction  of  his  “  Resist¬ 
ance  Thermometer,”  which  is  especially  useful  for  determining  the  temperature 
of  places  not  easily  accessible,  such  as  the  bottom  of  the  sea  :  “  A  fine  plati¬ 
num  wire  of  considerable  resistance  is  placed  in  a  close  case  at  the  spot  whose 
temperature  is  to  be  observed,  and  is  connected  by  means  of  thick  copper 
wires  with  the  place  where  the  observer  works.  A  similar  wire  in  a  closed 
case  is  placed  in  a  vessel  of  water,  and  an  arrangement  is  made  by  which  the 
electric  resistance  of  these  two  wires  may  be  compared.  I  he  water  in  the 
vessel  is  then  heated  or  cooled  till  the  resistance  of  the  wire  immersed  in  it 
is  equal  to  that  of  the  wire  at  the  distant  station.  The  temperature  of  the 
two  wires  must  then  be  equal,  and  by  observing  with  a  common  thermometer 
the  temperature  of  the  water  in  the  vessel,  that  of  the  distant  station  is 
obtained.  ’ 

Negretti  and  Zambra’s  Recording  and  Deep-Sea  Thermometer. 

This  thermometer  differs  from  all  other  registering  or  recording  ther¬ 
mometers  in  the  following  important  particulars  : 

I.  The  thermometer  contains  only  mercury,  without  any  admixture  ol 

alcohol  or  other  fluid.  ....  , 

II.  It  has  no  indices  or  springs,  and  its  indications  are  by  the  column  cf 

mercury  only. 

11 — 2 


164 


HEAT. 


F 


Fig.  1. 


III.  It  can  be  carried  in  any  position,  and  cannot  pos¬ 
sibly  be  put  out  of  order  except  by  actual  breakage  of  the 
instrument. 

And  lastly,  it  will  indicate  and  record  the  exact  tempe¬ 
rature  at  any  hour  of  the  day  or  night,  or  the  exact  tempe¬ 
rature  at  any  depth  of  the  sea,  irrespective  of  either  warm 
or  cold  currents  or  strata  through  which  the  thermometer 
may  have  to  pass  in  its  descent  or  ascent:  this  last  very 
special  quality  renders  this  thermometer  superior  for 
deep-sea  temperatures  to  any  others  ;  for  those  now  being 
used  in  the  “Challenger'’  sounding  expedition  are  liable 
to  give  erroneous  indications,  owing  to  their  indices  slip¬ 
ping,  and  otherwise  getting  deranged — (this  was  proved 
by  Messrs.  Negretti  and  Zambra  at  a  meeting  of  the  British 
Meteorological  Society) ;  and  under  certain  conditions  of 
tcniperatii' e  it  is  not  possible  by  the  old  thermometers  to 
obtain  true  temperatures  at  certain  depths  which  might  be 
required.  Annexed  is  a  copy  of  a  report  to  the  Admiralty 
from  Captain  G.  S.  Nares,  of  H.M.S.  “  Challenger,”  dated 
Melbourne,  March  25th,  1874,  which  we  have  taken  from 
“  Nature,”  July  30th,  1874,  proving  the  assertion. 

“  In  the  report  to  the  Admiralty  of  Capt.  G.  S.  Nares, 
of  H.M.S.  ‘Challenger,’  dated  Melbourne,  March  25,  1874, 
Capt.  Nares,  speaking  of  the  temperature  of  the  ocean, 
especially  near  the  pack  edge  of  the  ice,  says  : — ‘  At  a 
short  distance  from  the  pack,  the  surface  water  rose  to 
3 20,  but  at  a  depth  of  40  fathoms  wre  always  found  the 
temperature  to  be  290;  this  continued  to  300  fathoms,  the 
depth  in  which  most  of  the  icebergs  float,  after  which  there 
is  a  stratum  of  slightly  warmer  water  of  330  or  340.  As  the 
thermometers  had  to  pass  through  these  two  belts  of  water 
before  reaching  the  bottom,  the  indices  registered  those 
temperatures,  and  it  was  impossible  to  obtain  the  exact 
temperature  of  the  bottom  whilst  near  the  ice;  but  the 
observations  made  in  lower  latitudes  show  that  it  is  about 
310.  More  exact  results  could  not  have  been  obtained  even 
had  Mr.  Siemens’s  apparatus  been  on  board.’  It  seems  to 
us  that  the  difficulty  mentioned  is  one  which  would  cer¬ 
tainly  have  been  surmounted  by  Messrs.  Negretti  and 
Zambra’s  new  recording  thermometers,  a  description  of 
which  appeared  in  ‘  Nature,’  vol.  ix.  p.  387  ;  this  being 
exactly  one  of  the  cases  to  which  this  Instrument  is  pecu¬ 
liarly  adapted.  We  believe  the  inventors  and  makers  have 
greatly  improved  their  thermometer  since  our  description 
appeared,  and  no  doubt  means  will  be  taken  by  the 
Admiralty  to  transmit  one  to  the  ‘  Challenger.’” 

Description  of  the  Deep-Sea  Recording  Thcrmomelet . 

In  the  first  place,  it  must  be  observed  that  the  bulb  of 
the  thermometer  is  protected  so  as  to  resist  the  pressure 
of  the  ocean,  which  varies  according  to  depth,  that  of  3.000 


THE  DEEP-SEA  THERMOMETER. 


*65 


fathoms  being  something  like  three  tons  pressure  on  the  square  inch.  The 
manner  of  protecting  the  bulb  was  invented  by  Messrs.  Ne.retti  and  Zambra 
in  1857,  and  has  been  latterly  copied  by  other  persons  an  1  brought  out  as  a 
new  invention.  The  manner  of  protecting  the  bulb  has  been  described  by  the 
late  Admiral  R.  Fitzroy,  in  the  first  number  of  Meteorological  Papers,  page 
55,  published  July  5th,  1857,  as  follows  : 

“  Referring  to  the  erroneous  readings  of  all  thermometers,  consequent  on 
their  delicate  bulbs  being  compressed  by  the  great  pressure  of  the  ocean,  he 
says: — 4  With  a  view  to  obviate  this  failing,  Messrs.  Negretti  and  Zambra 
undertook  to  make  a  case  for  the  weak  bulbs,  wh'ch  should  transmit  tempe¬ 
rature,  but  resist  pressure.  Accordingly  a  tube  of 
thick  glass  is  sealed  outside  the  delicate  bulb, 
between  which  and  the  casing  is  a  space  all 
round,  which  is  nearly  filled  with  mercury.  The 
small  space  not  so  filled  is  a  vacuum,  into  which 
the  mercury  can  be  expanded  or  forced  by  heat 
or  mechanical  compression,  without  doing  injury 
to  or  even  compressing  the  inner  or  much  more 
delicate  bulb.” 

The  construction  of  this  instrument  for  deep- 
sea  temperatures  is  as  follows  : 

In  shape  it  is  like  a  syphon  with  parallel  legs, 
all  in  one  piece  and  having  a  continuous  com¬ 
munication.  as  in  the  annexed  Fig.  1.  The  scale 
of  the  thermometer  is  pivoted  on  a  centre,  and 
being  attached  in  a  perpendicular  position  to  a 
simple  apparatus  (which  will  be  presently  de¬ 
scribed),  is  lowered  to  any  depth  that  may  be 
desired.  In  its  descent  the  thermometer  acts  as 
an  ordinary  instrument,  the  mercury  rising  or 
falling  according  to  the  temperature  of  the 
stratum  through  which  it  passes;  but  so  soon  as 
the  descent  ceases,  and  a  reverse  motion  is  given 
to  the  line,  so  as  to  pull  the  thermometer  towards 
the  surface,  the  instrument  turns  once  on  its 
centre,  first  bulb  uppermost,  and  afterwards  bulb 
downwards.  This  causes  the  mercury,  which  was 
in  the  left-hand  column,  first  to  pass  into  the 
dilated  syphon  bend  at  the  top.  and  thence  into 
the  right-hand  tube,  where  it  remains,  indicating 
on  a  graduated  scale  the  exact  temperature  at 
the  time  it  was  turned  over.  1  he  woodcut,  Fig. 

1,  shows  the  position  of  the  mercury  after  the 
instrument  has  been  thus  turned  on  its  centre. 

A  is  the  bulb  ;  B  the  outer  coating  or  protecting 
cylinder  ;  c  is  the  space  of  rarefied  air,  which  is 
reduced  if  the  outer  casing  be  compressed  ;  D  is 
a  small  glass  plug  on  the  principle  of  Negretti  and 
Zambra’s  patent  m  iximum  thermometer,  which 
•  uts  off,  in  the  moment  of  turning,  the  mercury 
in  the  tube  from  that  of  the  bulb,  then,  by  in  ur-  FlG.  K. 


1 66 


HEAT. 


ing  that  none  but  the  mercury  in  the  tube  can  be  transferred  into  the  indicating 
column  ;  E  is  an  enlargement  made  in  the  bend  so  as  to  enable  the  mercury 
to  pass  quickly  from  one  tube  to  another  in  revolving ;  and  F  is  the  indicating 
tube  or  thermometer  proper.  In  its  action,  as  soon  as  the  thermometer  is 
put  in  motion,  and  immediately  the  tube  has  acquired  a  slightly  oblique  posi¬ 
tion,  the  mercury  breaks  off  at  the  point  D,  runs  into  the  curved  and  enlarged 
portion  E,  and  eventually  falls  into  the  tube  F,  when  this  tube  resumes  its 
original  perpendicular  position. 

The  contrivance  for  turning  the  thermometer  over  may  be  described  as  a 
frame  with  a  vertical  propeller ;  to  this  frame  the  instrument  is  pivoted.  On 
its  descent  through  the  water  the  propeller  is  lifted  out  of  gear  and  revolves 
freely  on  its  axis ;  but  so  soon  as  the  instrument  is  pulled  towards  the  surface, 
the  propeller  falls  into  gear  and  revolves  in  the  contrary  direction,  turning  the 
thermometer  over  once,  and  then  becoming  locked  and  immovable. 

Directionsfor  adjusting  the  Thermometer  previous  to  its  being  lowered  in  the  Sea. 

I.  The  mercury  must  all  be  in  the  left-hand  column. 

II.  The  short  peg  at  the  back  of  the  thermometer  must  be  in  front  of  the 

stop-plate  S  +  :  in  order  to  effect 
this,  pull  the  knob  which  stops 
the  thermometer,  and  slightly 
turn  the  propeller,  to  make  the 
thermometer  ad  vance  sufficiently 
to  escape  the  stop-plate. 

Negretti  and  Zambra’s  atmo¬ 
spheric  recording  thermometer, 
Fig.  L,  differs  from  the  deep- 
sea  thermometer  by  its  not  hav¬ 
ing  the  double  or  protected  bulb, 
it  not  being  required  for  resisting 
pressures.  In  this  case  the  in¬ 
strument  is  turned  over  by  a 
simple  clock  movement,  which 
can  be  set  to  any  hour  it  may 
be  desirable  ;  the  thermometer 
is  fixed  on  the  clock,  and  when 
the  hand  arrives  at  the  hour 
determined  upon,  and  to  which 
the  clock  is  set  as  in  setting  an 
al  irum  clock,  a  spring  is  released 
and  the  thermometer  turns  over 
as  before  described. 

Messrs.  Negretti  and  Zambra 
have  arranged  a  wet  and  dry  bulb 
hygrometer  upon  the  same  plan. 

The  Pyrometer. 

One  of  the  most  celebrated  contrivances  for  estimating  high  temperatures 
was  that  of  Mr.  Wedgwood  ;  but,  as  the  indications  depended  on  the  con¬ 
traction  of  clay  cylinders,  which  will  contract  as  much  by  the  long  continuance 
of  a  comparatively  low  heat  as  by  a  short  continuance  of  a  high  one,  they 
were  enormously  exaggerated,  and  could  not  be  correct.  The  late  Professor 
Daniell  improved  greatly  upon  Wedgwood’s  instrument,  and,  by  using  the 


Fig.  l. 


THE  PYROMETER. 


167 


linear  expansion  of  bars  of  metal,  arrived  much  nearer  to  a  correct  estimate 
of  temperatures  above  a  dull  red  heat.  Daniell  calls  his  instrument  the  register 
pyrometer,  and  describes  it  as  follows :  “  It  consists  of  two  parts,  which  may 
be  distinguished  as  the  register  and  the  scale.  The  register  is  a  solid  bar  of 
blacklead  earthenware,  highly  baked.  In  this  a  hole  is  drilled,  into  which  a 
bar  of  any  metal,  6  in.  long,  may  be  dropped,  and  which  will  then  rest  upon 
its  solid  end.  A  cylindrical  piece  of  porcelain,  called  the  index,  is  then  placed 
upon  the  top  of  the  bar,  and  confined  in  its  place  by  a  ring  or  strap  of  platinum 
passing  round  the  top  of  the  register,  which  is  partly  cut  away  at  the  top,  and 
tightened  by  a  wedge  of  porcelain.  When  such  an  arrangement  is  exposed 
to  a  high  temperature,  it  is  obvious  that  the  expansion  of  the  metallic  brr 
will  force  the  index  forward  to  the  amount  of  the  excess  of  its  expansion 
over  that  of  the  blacklead,  and  that, 
when  cooled,  it  will  be  left  at  the 
point  of  greatest  elongation.  What  is 
now  required  is  the  measurement  of 
the  distance  which  the  index  has  been 
thrust  forward  from  its  first  position ; 
and  this,  though  in  any  case  but  .small, 
may  be  effected  with  great  precision 
by  means  of  the  scale.  This  is  in¬ 
dependent  of  the  register,  and  con¬ 
sists  of  two  rules  of  brass  accurately 
joined  together  at  a  right  angle  by 
their  edges,  and  fitting  square  upon 
two  sides  of  the  blacklead  bar.  At  one 
end  of  this  double  rule  a  small  plate  of 
brass  projects  at  a  right  angle,  which 
may  be  brought  down  upon  the  shoul¬ 
der  of  the  register,  formed  by  a  notch 
cut  away  for  the  reception  of  the  index. 

A  movable  arm  is  attached  upon  this 
frame,  turning  upon  its  fixed  extremity 
upon  a  centre,  and  at  its  other  carry¬ 
ing  an  arc  of  a  circle,  whose  radius  is 
exactly  5  in.,  accurately  divided  into  degrees  and  thirds  of  a  degree.  Upon 
this  arm  at  the  centre  of  the  circle  another  lighter  arm  is  made  to  turn,  one 
end  of  which  carries  a  nonius  with  it,  which  moves  upon  the  face  of  the  arc, 
and  subdivides  the  former  graduation  into  minutes  of  a  degree  ;  the  other  end 
crosses  the  centre,  and  terminates  in  an  obtuse  steel  point,  turned  inwards  at  a 
right  angle. 

“When  an  observation  is  to  be  made,  a  bar  of  platinum  or  malleable  iron 
is  placed  in  the  cavity  of  the  register;  the  index  is  to  be  pressed  down  upon 
it,  and  firmly  fixed  in  its  place  by  the  platinum  strap  and  porcelain  wedge. 
The  scale  is  then  to  be  applied  by  carefully  adjusting  the  brass  rule  to  the 
sides  of  the  register,  and  fixing  it  by  pressing  the  cross  piece  upon  the  shoulder, 
and  placing  the  movable  arm  so  that  the  steel  point  of  the  radius  may  drop 
into  a  small  cavity  made  for  its  reception,  and  coinciding  with  the  axis  of  the 
metallic  bar. 

“  The  minutes  of  the  degree  must  then  be  noted,  which  the  nonius  indicates 
upon  the  arc.  A  similar  observation  must  be  made  after  the  register  has  been 


i68 


HEAT. 


exposed  to  the  increased  temperature  which  it  is  designed  to  measnre,  and 
again  cooled,  and  it  will  be  found  that  the  nonius  has  been  moved  forward  a 
certain  number  of  degrees  or  minutes,  as  shown  at  F  igs.  151  and  152.” 

Fig.  15  1  represents  the  register;  A  is  the  bar  of  black  lead;  a  the  cavity 
for  the  reception  of  the  metallic  bar;  c c'  is  the  index,  or  cylindrical  piece  of  • 
porcelain  ;  d,  the  platinum  band,  with  its  wedge,  e. 

Fig.  152  is  the  scale  by  which  the  expansion  is  measured:  f  is  the  greater 
rule,  upon  which  the  smaller,  g,  is  fixed  square.  The  projecting  arc  h  is  also 
fitted  square  to  the  ledge  under  the  platinum  band  d. 

D  is  the  arm  which  carries  the  graduated  arc  of  the  circle  E.  fixed  to  the  rule 
f  and  movable  upon  the  centre  i. 

C  is  the  lighter  bar  fixed  to  the  first,  and  moving  upon  the  centre  k. 

H  is  the  nonius  at  one  of  its  extremities,  and  m  the  steel  point  at  the  other. 

The  rule^  admits  of  adjustment  on  f,  so  that  the  arm  h  may  be  adjusted 
to  the  centre  i,  in  order  thabat  the  commencement  of  an  experiment  the  nonius 
may  rest  at  the  beginning  of  the  scale. 

The  term  “  nonius,”  used  by  Daniell,  is  only  another  name  for  vernier,  a 
contrivance  for  measuring  intervals  between  the  divisions  of  graduated  scales 
on  circular  instruments. 

The  scale  of  this  pyrometer  is  readily  connected  with  that  of  the  thermo¬ 
meter  by  immersing  the  register  in  boiling  mercury,  whose  temperature  is  as 
constant  as  that  of  boiling  water,  and  has  been  accurately  determined  by  the 
thermometer. 

The  amount  of  expansion  for  a  known  number  of  degrees  is  thus  deter¬ 
mined,  and  the  volume  of  all  other  expansions  may  be  considered  as  propor¬ 
tional. 

The  melting-point  of  cast  iron  has  been  thus  ascertained  to  be  2786°,  and 
the  highest  temperature  of  a  good  wind-furnace  about  3300° — points  which 
were  estimated  by  Mr.  Wedgwood  at  20,577°  and  32,277  respectively. 

Mr.  Wedgwood,  indeed,  makes  an  observation  which  is  calculated  to  throw 
suspicion  upon  the  accuracy  of  his  results  ;  for  he  says,  “We  see  at  once  how 
small  a  portion  (of  the  rays  of  heat)  is  concerned  in  animal  and  vegetable  life, 
and  in  the  ordinary  operations  of  nature.  From  freezing  to  vital  heat  is  barely 
1 -500th  part  of  the  scale — a  quantity  so  inconsiderable  relatively  to  the  whole 
that  in  the  higher  stages  of  ignition  ten  times  as  much  might  be  added  or 
taken  away  without  the  least  difference  being  discoverable  in  any  of  the 
appearances  from  which  the  intensity  of  fire  has  hitherto  been  judged  of.” 

Now  this,  remarks  Daniell,  “is  utterly  unlike  the  gradual  progression  by 
which  the  operations  of  nature  are  generally  carried  on ;  and  the  fact  is,  that 
a  regular  transition  may  be  traced  from  one  remarkable  point  of  temperature 
to  another.” 

Thus  from  the  freezing  of  water,  320,  to  vital  heat  in  man  is  6o°. 

60  X  3—  180°  Boiling  water. 

60 x  7=  420°  Melted  tin. 

60X10=  6oo°  Boiling  mercury. 

60  x  1 5  =  900°  Red  heat. 

60  X  3 1  =  1 86o°  M  elting  silver. 

60x45=2700°  Melting  cast  iron. 

60x55=3300°  Highest  heat  of  wind-furnace. 

Before  the  invention  of  the  register  pyrometer,  the  expansion  of  solids 
had  never  been  ascertained  beyond  the  temperature  of  527°:  the  following 


THE  PYROMETER . 


169 


table  exhibits  the  progressive  amount  of  several  metals  to  their  point  of  fusion, 
as  determined  by  Daniell’s  pyrometer: 


PROGRESSIVE  DILATATION  OF  SOLIDS. 
One  inilloti  parts  at  62°. 


At  j  a0. 

At  662°. 

At  Fusing-point 

Blacklcad  ware  . 

1,000,244 

1,000  703 

Wedgwood  ware  . 

1,000,735 

1,002,995 

Platinum 

i,ooo,735 

1,002,995 

1 ,009,926 

(maximum,  but  not  fused). 

Iron,  wrought 

1 ,000,984 

1,004,483 

1,018,378 

to  the  fusing-point  of  cast  iron. 

Iron,  cast 

Gold  . 

1,000,893 

1,003,943 

1,016,389 

1,001,025 

1,004,238 

Copper 

1,001,430 

1,006,347 

1,024,976 

Silver  . 

1.001,626 

1,006,886 

1,020,640 

Zinc 

1,002,480 

1,008,527 

1,012,621 

Lead  . 

1,002,323 

1,009,072 

Tin 

1,001,472 

... 

1,003,798 

Professor  Daniell  concludes  his  dissertation  by  the  following  passage, 
which  is  quite  in  accordance  with  those  notions  which  Tyndall  has  so  ably 
contended  for — viz.,  that  heat  is  a  mode  of  motion: — “The  amount  of  the  force 
which  produces  these  expansions  and  contractions,  measured  by  any  oppo¬ 
sing  force,  that  of  cohesion,  for  instance,  is  enormous. 

“Some  idea  may  be  formed  of  it,  when  it  is  understood  that  it  is  equal  to 
the  mechanical  force  which  would  be  necessary  to  produce  similar  effects  in 
stretching  or  compressing  the  solids  in  which  they  take  place.  Thus,  a  bar 
of  iron  heated  so  as  to  increase  its  length  a  quarter  of  an  inch,  by  this  slow 
and  quiet  process  exerts  a  power  against  any  obstacle  by  which  it  may  be 
attempted  to  confine  it,  equal  to  that  which  would  be  required  to  reduce  its 
length  by  compression  to  an  equal  amount.  On  withdrawing  the  heat,  it 
would  exert  an  equal  power  in  returning  to  its  former  dimensions.” 

M.  Molard  used  this  great  moving  force  to  restore  the  walls  of  a  building  to 
the  perpendicular  which  had  been  bulged,  anxl  the  same  principle  was  used  at 
the  Cathedral  of  Armagh. 


- ♦ - 

THE  EXPANSION  OF  GASES. 

We  now  come  to  the  most  expansible  bodies — viz.,  the  gases;  and,  although 
at  first  there  was  considerable  doubt  whether  they  all  expanded  alike,  because 
the  experimentalists  had  neglected  to  remove  the  moisture — the  aqueous 
vapour — from  them,  it  was  finally  discovered,  not  only  by  Gay-Lussac  in 
Paris,  but  by  our  own  countryman,  the  illustrious  Dr.  Dalton,  that  all  gases 
expand  alike  with  the  same  amount  of  heat,  and  that  the  rate  of  dilatation 
continues  uniform  for  all  temperatures.  In  discovering  the  expansibility 


170 


HJZAT. 


of  liquids  it  was  found  that  cohesion  was  not  quite  overcome,  and  that  there 
was  still  a  considerable  amount  of  that  force  which  tended  to  keep  the  par¬ 
ticles  in  contact.  This,  however,  is  not  the  case  with  gases ;  the  cohesive 
power  is  for  the  time  completely  overcome  by  the  motion  of  heat.  Sir  H. 
Davy  speaks  emphatically  upon  this  motion  in  his  “  Chemical  Philosophy.” 
“  It  seems  possible  to  account  for  all  the  phenomena  of  heat,  if  it  be  supposed 
that  in  solids  the  particles  are  in  a  constant  state  of  vibratory  motion,  the 
particles  of  the  hottest  bodies  moving  with  the  greatest  velocity  and  through 
the  greatest  space ;  that  in  fluids  and  elastic  fluids,  besides  the  vibratory 
motion,  which  must  be  conceived  greatest  in  the  last,  the  particles  have  a 
motion  round  their  own  axes  with  different  velocity,  the  particles  of  elastic 
fluids  (gases)  moving  with  the  greatest  quickness  ;  and  that  in  ethereal  sub¬ 
stances  the  particles  move  round  their  own  axes,  and  separate  from  each  other, 
penetrating  in  right  lines  through  space.  Temperature  may  be  conceived  to 
depend  upon  the  velocity  of  the  vibration,  increase  of  capacity  in  the  motion 
being  performed  in  greater  space  ;  and  the  diminution  of  temperature  during 
the  conversion  of  solids  into  fluids  or  gases  may  be  explained  on  the  idea  of 
the  loss  of  vibratory  motion  in  consequence  of  the  revolution  of  particles 
round  their  axes  at  the  moment  when  the  body  becomes  fluid  cr  aeriform,  or 
from  the  loss  of  rapidity  of  vibration  in  consequence  of  the  motion  of  the 
particles  through  space.” 

It  has  been  proved  that  gases  expand  by  1 -490th  of  their  own  volume  tor 
every  degree  of  Fahrenheit’s  scale  between  the  freezing-point,  32°  and  the 
boiling-point  of  water,  21 2°,  and  so  on  at  higher  or  lower  temperature,  pro¬ 
vided  the  pressure  of  the  air  remains  the  same.  If  the  Centigrade  scale  is 
used,  the  ratio  of  expansion  of  any  gas  will  be  1-2731-d  of  its  volume  for  every 
degree. 

490  cubic  inches  of  air  at  320  become  491  at  33° 

491  „  „  33  „  492  „  34 

492  „  „  34  „  493  „  35 

From  a  most  careful  series  of  experiments  it  has  been  determined  that 

“  the  coefficient  of  expansion  ”  of  all  gases,  expressed  in  decimals,  is  o-oo,366. 
These  figures  are  near  enough  for  all  ordinary  calculations,  although  it  must 
be  observed  that,  speaking  rigidly,  this  is  not  exactly  the  case,  except  probably 
with  the  three  permanent  gases,  oxygen,  hydrogen,  and  nitrogen, — in  all  the 
other  gases  and  vapours  the  expansion  being  greatest  for  those  which  are 
most  readily  condensible. 

M.  Regnault  has  made  the  most  elaborate  and  careful  experiments,  and 
determined  that  one  thousand  volumes  of  certain  gases  at  o°  C.  or  320  F. 
(the  pressure  of  the  air  remaining  unchanged)  become  expanded  in  the  fol¬ 
lowing  proportions  when  heated  to  ioo°  C.,  or  21 2°  F. : 


Aii- 

Carbonic  acid 
Carbonic  oxide 
Cyanogen  . 


1,367-06 

b37o-99 

1,366-88 

1,387-67 


Hydrogen  . 
Hydrochlorine  acid 
Nitrogen 
Nitric  oxide 


1.366- 13 
1,368-12 

1.366- 82 

I,37r95 


It  will  be  apparent  that  hydrogen  expands  the  least,  and,  as  might  be 
expected,  cyanogen,  which  is  liquified  with  comparative  ease,  is  much  higher 
— viz.,  1,387*67.  It  is,  therefore,  apparent  that  if  the  coefficient  of  expansion 
remains  the  same  with  all  gases,  that  cyanogen  should  have  been  represented 


7 HE  EXPANSION  OF  GASES. 


1 7 1 


by  the  same  figures  as  those  which  belong  to  air— instead  of  being  0  00,387  to 
0  00, 367  atmospheric  air.  The  conversion  of  this  property  of  expansion  into 
power  or  motion  is  well  described  by  Tyndall  : — “  Suppose  !  have  a  quantity 
of  air  contained  in  a  very  tall  cylinder  (a  b,  Fig.  153),  the  transverse  section 
of  which  is  one  square  inch  in  area.  Let  the  top,  A,  of  the 
cylinder  be  open  to  the  air,  and  let  P  be  a  piston,  which,  for 
reasons  to  be  explained  immediately,  I  will  suppose  to  weigh 
two  pounds  one  ounce,  and  which  moves  air-tight  and  without 
friction  up  or  down  in  the  cylinder.  At  the  commencement  of 
the  experiment  let  the  piston  be  at  the  point  P  of  the  cylinder, 
and  let  the  height  of  the  cylinder  from  its  bottom  B  to  the  point 
P  be  273  inches,  the  air  underneath  the  piston  being  at  a  tem¬ 
perature  of  o°  C.  Then,  on  heating  the  air  from  o°  to  iJ  C.,  the 
piston  will  rise  one  inch;  it  will  now  stand  at  274  inches  above 
the  bottom.  If  the  temperature  be  raised  two  degrees,  the  pis¬ 
ton  will  stand  at  275  ;  if  raised  three  degrees,  it  will  stand  at 
276;  if  raised  ten  degrees,  it  will  stand  at  283;  if  100  degrees, 
it  will  stand  at  373  inches  above  the  bottom;  finally,  if  the  tem¬ 
perature  were  raised  to  2730  C.,  it  is  quite  manifest  that  273 
inches  would  be  added  to  the  height  of  the  column  ;  or,  in  other 
words,  that  by  heating  the  air  to  2730  C.  its  volume  would  be 
I?  doubled.  The  gas  in  this  experiment  executes  work.  In  expand¬ 
ing  from  P  upwards,  it  has  to  overcome  the  downward  pressure 
of  the  atmosphere,  which  amounts  to  1 5  lbs.  on  every  square 
inch,  and  also  the  weight  of  the  piston  itself,  which  is  2  lbs.  1  oz. 
Hence,  the  section  of  the  cylinder  being  one  square  inch  in 
area,  in  expanding  from  P  to  P'  the  work  done  by  the  gas  is 
equivalent  to  the  raising  a  weight  of  17  lbs.  1  oz.,  or  273  ounces, 
to  a  height  of  273  inches.  It  is  just  the  same  as  what  it  would 
accomplish  if  the  air  above  P  were  entirely  abolished,  and  a 
piston  weighing  17  lbs.  1  oz.  were  placed  at  P. 

“  Let  us  now  alter  our  mode  of  experiment,  and,  instead  of 
allowing  our  gas  to  expand  when  heated,  let  us  oppose  its  ex¬ 
pansion  by  augmenting  the  pressure  upon  it;  in  other  words, 
let  us  keep  its  volume  constant  while  it  is  being  heated. 

“Suppose,  as  before,  the  initial  temperature  of  the  gas  to  be 
0°  C,  the  pressure  upon  it,  including  the  weight  of  the  piston 
P,  being  as  formerly  273  ounces.  Let  us  warm  the  gas  from  o° 
C.  to  C. ;  what  weight  must  we  add  at  P  in  order  to  keep  its 
volume  constant?  Exactly  one  ounce. 

“  But  we  have  supposed  the  gas  at  the  commencement  to  be  under  a  pres¬ 
sure  of  273  ounces,  and  the  pressure  it  sustains  is  the  measure  of  its  elastic 
force  ;  hence,  by  being  heated  t°,  the  elastic  force  of  the  gas  has  augmented 
by  i-273rd  of  what  it  possessed  at  o°.  If  we  warm  it  2°,  two  ounces  must 

be  added  to  keep  its  volume  constant ;  if  30,  three  ounces  must  be  added  ; 

and  if  we  raise  its  temperature  2730,  we  should  have  to  add  273  ounces, 
that  is,  we  should  have  to  double  the  original  pressure  to  keep  its  volume 
constant.  o  , 

“  In  the  first  case  marked  out,  it  is  shown  that  by  heating  the  air  to  273  L. 
its  volume  would  be  doubled.  In  the  second,  that  by  compressing  the  air  with 
273  ounces  we  may  heat  it  to  27  f  C.,  and  have,  consequently,  double  the 


o*o 


B 


Fig.  153. 


172 


HEAT. 


original  pressure  to  keep  the  air  confined  to  the  same  volume.  In  fact,  the 
volume  being  kept  constant,  the  elastic  force  is  doubled. 

“  But  are  the  absolute  quantities  of  heat  imparted  in  both  cases  the  same  ? 
By' no  means.  Supposing  that  to  raise  the  temperature  of  the  gas,  whose 
volume  is  kept  constant,  2730,  ten  grains  of  combustible  matter  are  necessary; 
then  to  raise  the  temperature  of  the  gas,  whose  pressure  is  kept  constant,  an 
equal  number  of  degrees  would  require  the  combustion  of  145  grains  of  the 
same  combustible  matter.  The  heat  produced  by  the  combustion  of  the  addi¬ 
tional  4}  grains  in  the  latter  case  is  entirely  consumed  in  lifting  the  weight. 
Using  the  accurate  numbers,  the  quantity  of  heat  applied  when  the  volume  is 
constant  is,  to  the  quantity  applied  when  the  pressure  is  constant,  in  the  pro¬ 
portion  of  1  to  1 ’42 1. 

“  This  extremely  important  fact  constituted  the  basis  from  which  the 
mechanical  equivalent  of  heat  was  first  calculated.” 

Various  methods  have  been  contrived  to  determine  the  amount  of  expansion 
of  gases  when  subjected  to  a  uniform  pressure,  and  one  of  the  most  simple  is 
that  of  Monsieur  Pouillet  (Fig.  154),  described  by  Lardner. 

“  An  iron  syphon  tube,  D  c,  is  formed 
with  short  legs,  from  the  bottom  of  which 
proceeds  a  pipe  with  a  stop-cock  F,  under 
which  is  placed  a  cistern  or  reservoir  G.  In 
the  legs  of  the  syphon  D  c  are  inserted  two 
glass  tubes,  D  E  and  C  B,of  more  than  thirty 
inches  in  height.  The  tube  D  E  is  open  at 
the  top ;  the  tube  C  D  is  closed  at  the  top, 
but  has  a  horizontal  branch  united  to  it,  at 
B,  which  is  connected  with  a  tube,  A  B, 
made  of  platinum,  which  terminates  in  a 
hollow  globe  or  ball,  A,  also  made  of  pla¬ 
tinum.  In  the  tube  BA  is  fixed  a  stop¬ 
cock  in  order  to  communicate  at  pleasure 
with  the  atmospheric  air. 

“  The  stop-cock  F  being  closed,  and  the 
stop-cock  in  the  tube  B  A  being  open,  mer¬ 
cury  is  poured  into  the  tube  D  E,  so  as  to 
fill  the  glass  tubes  D  E  and  c  B  nearly  to 
the  top.  Since  the  tubes  D  E  and  C  B  both 
communicate  with  the  external  air,  the 
columns  of  mercury  in  them  will  stand  at 
the  same  level. 

“To  determine  the  expansion  which  air  suffers  when  raised  from  the  freezing- 
point  to  the  boiling-point  under  uniform  pressure,  let  the  ball  a  be  immersed  in 
a  bath  of  melting  ice,  so  as  to  reduce  the  air  included  in  it  to  the  freezing-point. 
Let  the  stop-cock  in  the  tube  b  a  be  then  closed,  and  let  the  bulb  A  be  removed 
to  a  bath  of  boiling  water.  The  air  in  the  bulb,  expanding,  will  press  down  the 
column  of  mercury  in  B  c,  and  will  cause  the  column  in  d  e  to  rise  ;  so  that  the 
levels  of  the  two  columns  will  no  longer  coincide.  But  they  may  be  equalized 
by  opening  the  stop-cock  f,  and  allowing  mercury  to  flow  into  the  reservoir  G 
from  the  syphon  until  the  levels  in  the  two  legs  come  to  the  same  point.  When 
that  is  accomplished,  the  pressure  upon  the  expanded  air  included  in  the  bulb 
A,  and  the  tube  communicating  with  it,  will  be  equal  to  that  of  the  atmosphere, 
and  equal  to  that  which  the  same  air  has  when  at  the  freezing-point. 


THE  EXPANSION  OF  GASES. 


i73 


u  The  capacity  of  the  tube  C  B  being  known,  the  volume  which  corresponds 
to  any  kng  n  of  it  will  be  also  known  ;  also  the  increment  of  volume  which 
the  air  has  suffered  by  expansion  will  be  indicated  by  the  height  through 
which  the  mercury  has  fallen  in  the  tube  C  D.  This  increment,  therefore,  will 
be  the  dilatation  of  the  air  included  in  the  bulb  A  and  the  communicating  tube 
between  the  freezing  and  the  boiling  points.  In  the  same  manner,  by  this 
apparatus,  the  dilatation  corresponding  to  any  change  whatever  of  temperature 
under  a  given  pressure  can  be  ascertained.” 

The  expansion  of  air  by  heat,  and  the  uniformity  with  which  it  takes  place, 
suggested  at  a  very  early  period  of  science  the  use  of  air-thermometers,  which 
are  the  most  delicate  and,  with  certain  precautions,  the  most  reliable  in  certain 
cases  where  high  temperatures  have  to  be  determined.  The  first  was  formerly 
supposed  to  have  been  constructed  by  a  learned  Italian  physician,  named 
Sagredo,  about  the  year  1 590.  It  is  sometimes  attributed  to  Cornelius  Drebel, 

who  introduced  it  in  the  year  i6ro;  but  this  is  a  mis¬ 
take.  Drebel  followed  Sagredo,  and  therefore  cannot 
be  the  first  inventor,  although  there  is  every  reason  to 
suppose  th.it  he  made  his  air-thermometer  in  perfect 
ignorance  of  what  Sagredo  had  already  done.  It  is 
now  determined  that  the  first  inventor  of  the  air- 
thermometer  was  Galileo  (see“  Memoiresur  la  Deter¬ 
mination  de  l’Echelle  du  Thermometre  de  l'Academie 
del  Cimento,”  par  S.  Libri,  Ann.  de  Chemic  45,  1830. 

The  construction  is  very  simple:  it  consists  of  a 
glass  tube  at  the  end  of  which  a  bulb  or  ball  is  blown; 
this  tube,  with  its  ball,  is  then  fitted  into  some  conve¬ 
nient  glass  vessel  or  bottle,  containing  a  little  coloured 
water.  On  tk 1  application  of  heat,  either  from  the 
palm  of  the  hand  or  the  flame  of  a  spirit-lamp,  a  por¬ 
tion  of  the  air  in  the  tube  is  expelled,  and,  when  cold, 
th*e  water  ascends  to  fill  its  place;  the  rise  or  fall  of 
this  column  of  coloured  water  by  the  expansion  or 
contraction  of  the  air  in  the  bulb  is  supposed  to  indi¬ 
cate  the  difference  of  temperature. 

It  was  soon  discovered  that  this  air-thermometer 
was  not  correct  in  its  indications,  and  was,  in  fact, 
affected  by  the  pressme  of  air:  when  the  barometer 
fell,  the  air  expanded  in  the  bulb,  and  the  coloured 
fluid  was  driven  downwards;  or,  on  the  contrary,  if  the 
barometer  rose,  the  air,  contracted  by  the  increased 
pressure  on  the  liquid,  was  pushed  higher  up  the  tube. 
Sir  John  Leslie  greatly  improved  upon  the  rude  appa¬ 
ratus  already  described,  and  invented  a  very  elegant  in- 
FlG.  15  5.  strument,  called  the  Differential  A  ir  Thermometer  ( F  ig. 

The  Air-Thermometer  1 56),  which  has  been  of  the  greatest  use  in  the  refined 
of  Sanctorius.  experimental  researches  made  for  the  elucidation  of 
the  more  obscure  properties  of  the  force  called  heat. 

It  consists  of  two  glass  bulbs  or  balls  connected  together  by  a  tube  bent 
twice  at  right  angels.  The  balls  contain  air,  and,  just  before  they  are  her¬ 
metically  closed,  a  little  sulphuric  acid,  coloured  with  carmine,  is  introduced, 
so  that  it  rises  to  about  half  the  height  of  the  two  tubes  bent  at  right  angles. 


174 


HEAT. 


The  ball  left  open  for  the  introduction  of  the 
coloured  fluid  is  now  finally  closed,  and  as  both 
bulbs  must  be  equally  affected  by  changes  of  tem¬ 
perature  in  the  surrounding  air,  the  liquids  in  the 
tubes  remain  in  equilibrium. 

If,  however,  one  of  the  balls  is  grasped  by  the 
hand,  the  air  expands,  and  the  fluid  is  driven  up 
the  other  tube,  which  is  provided  with  a  proper 
scale;  thus  at  any  moment,  by  placing  one  ball  in 
a  particular  spot  where  heat  is  to  be  discovered, 
the  expansion  of  the  air  becomes  a  most  sensitive 
and  delicate  means  of  appreciating  any  small 
amount  of  heat. 


Fig.  156.-  Leslie’s  Differ¬ 
ential  Thermometer. 


Fig.  157. --Differential  Thermometer  used  to 
discover  Focus  of  Heat  Rays. 


CONDUCTION. 

Our  ideas  of  this  property  of  heat,  of  travelling  along  and  through  material 
substances,  are  quickly  formed  and  put  in  practice.  If  a  bar  of  iron  and  a  rod 
of  glass  are  thrust  between  the  bars  of  a  grate  containing  burning  fuel,  we 
soon  learn  which  we  may  first  touch  or  take  out  with  impunity.  The  iron 
rapidly  becomes  so  hot  throughout  its  length  and  breadth,  that  we  cannot 
lay  hold  of  it ;  the  glass  rod  may  be  quite  softened  within  a  few  inches  of 
the  hand,  and  yet  the  heat  is  not  sensibly  felt  or  becomes  so  great  as  to 
prevent  the  rod  of  glass  being  held  in  the  hand:  in  the  one  case  there  appear 
to  be  regular  stepping-stones  across  which  the  heat  may,  as  it  were,  take  its 
way;  in  the  other  there  is  no  regular  path  provided,  and  the  travelling  power 
of  the  heat  is  interfered  with,  and  so  greatly  impeded  that  a  considerable 
time  must  elapse  before  any  sensible  progress  or  travelling  of  the  heat  can 
be  recorded.  Thus  in  early  days  the  wise  men  of  the  period  rudely  divided 
all  substances  into  conductors  and  non-conductors  of  heat.  Such  a  division, 
however,  is  not  in  accordance  with  nature;  there  are  intermediate  conditions 
of  conductivity,  and  thus  we  come  to  speak  of  good  and  bad  conductors  of 
heat. 


CONDUCTION. 


i75 


In  regarding  heat  by  the  dynamical  theory,  the  student  can  have  no  diffi¬ 
culty  in  understanding  that  the  position  of  the  solid  substance  under  exami¬ 
nation  in  the  list  of  good  or  bad  conductors  must  depend  greatly  upon  its 
physical  structure.  The  metals  are  good  conductors ;  there  is  uniformity  of 
internal  structure,  and  the  vibratory  movement  necessary  to  set  the  heat¬ 
waves  in  motion  is  regular  and  not  interfered  with ;  moreover,  the  particles 
are  in  close  contact.  Glass  is  a  bad  conductor,  because  those  conditions 
which  are  necessary  for  the  setting  up  of  molecular  motion  are  not  fulfilled  ; 
the  vibrations  are  not  communicated  steadily  from  molecule  to  molecule,  but 
broken  up  and  thrown  into  confusion  ;  the  glass  has  no  regular  molecular  homo¬ 
geneity — it  is  too  heterogeneous.  Any  substance  which  can  transmit  molecular 
motion  is  a  good  conductor  of  heat,  and  those  bodies  which  do  not  transmit 
this  motion  readily  are  bad  conductors. 


Figs.  158  and  159. — Griffiths’  experiment. 


The  difference  oetween  the  conducting  power  of  a  metal,  an  earth,  and  an 
earthy  compound  may  be  illustrated  by  th?:  following  simple  and  instructive 

experiment :  * 

Provide  solid  cylinders  of  these  three  materials,  viz.,  iron,  sandstone,  and 
chalk ;  let  these  be  1  in.  in  diameter  and  6  in.  long,  and  perfectly  flat  at  each 

of  their  ends. 

Place  a  cup,  containing  an  ounce  of  tallow,  upon  the  warm  hob  of  the  grate; 
and  when  the  tallow  is  perfectly«melted,  dip  into  it  for  about  half  an  inch  one 
end  of  the  iron  cylinder,  and  then  lift  it  out;  a  portion  of  tallow  will  adhere, 
and  quickly  become  solid,  because  the  iron,  by  good  conducting  power,  deprives 
it  of  the  heat  of  fluidity. 

Dip  one  end  of  each  of  the  other  cylinders  in  the  same  way ;  they  will 
attract  or  absorb  a  considerable  portion  of  the  melted  tallow,  and  some  time 
will  be  required  before  it  will  become  equally  solid  with  that  on  the  iron 
cylinder,  because  sandstone  and  chalk  have  not  sufficient  conducting  power 
to  deprive  it  of  heat  in  a  similar  degree. 

Dip  the  end  of  all  three  cylinders  again,  and  lift  them  out,  and,  when  the 
tallow  becomes  solid,  dip  them  again,  and  lift  them  out  until  they  have  all 
obtained  an  equal  coating  of  tallow;  then  allow  them  to  cool.  Pour  boiling 
water  into  a  “hot-water  plate,”  and  place  the  three  cylinders  to  stand  upon  it 
at  equal  distances,  with  their  coated  ends  uppermost,  as  shown  in  Fig.  1 58. 


*  "Chemistry  of  the  Four  Seasons,”  Griffiths. 


176 


HEAT. 


In  the  course  of  a  few  minutes,  the  iron  will  again  prove  its  good  conducting 
power  by  melting  the  tallow;  but  the  sandstone  and  chalk  will  prove  their 
bad  conducting  power  by  the  tallow  remaining  solid  during  the  whole  time 
that  the  water  is  cooling  down  to  common  temperature. 

By  reversing  the  arrangement  of  the  last  experiment,  namely,  by  applying 
heat  above,  instead  of  beneath,  the  cylinders,  it  can  be  proved  that  neither 
the  conducting  power  of  the  iron  nor  the  non-conducting  power  of  the  sand¬ 
stone  and  chalk  are  in  the  least  degree  affected  or  modified. 

Let  the  iron  cylinder  be  again  coated  with  tallow,  but  pare  away  all  from 
its  circular  extremity,  that  it  may  now  stand  firmly  upon  this,  and  have  only 
a  ring  of  tallow,  about  half  an  inch  wide,  around  its  circumference ;  do  the 
same  with  the  cylinders  of  sandstone  and  chalk;  then  set  the  three  at  equal 
distances  within  a  circle  similar  in  diameter  to  the  bottom  of  the  hot-water 
plate,  that  they  may  form  a  tripod  for  its  support  (this  arrangement  must  be 
made  upon  a  steady  table) ;  then  remove  the  plate,  without  disturbing  the 
cylinder,  fill  it  with  boiling  water,  and  carefully  replace  it  to  stand  upon  them, 
as  represented  in  Fig.  159. 

The  three  cylinders  will  now  be  subjected  to  heat  applied  from  above,  instead 
of  from  below,  as  in  the  last  experiment  (Fig.  158);  but  this  arrangement  will 
cause  no  difference  in  their  conducting  power,  or  non-conducting  power,  as 
will  be  proved  in  the  course  of  a  few  minutes  by  the  ring  of  tallow  melting 
from  the  iron  cylinder,  whilst  that  upon  each  of  the  other  cylinders  remains 
solid  as  before. 

Starting  with  gold,  and  taking  it  as  the  type  of  a  good  conductor,  and 
giving  it  the  first  place  in  a  scale  amounting  to  100,  we  have  the  following 
tabulated  results  obtained  by  Franklin  and  Igenliausz,  by  watching  the  rate 
at  which  wax  was  melted  at  the  end  of  bars  of 


Gold  . 

Platinum 

Silver 

Copper  . 

Iron 

Zinc 


.  j  00  00 

Tin . 

.  9810 

Lead  . 

.  97-30 

Marble  . 

.  89-82 

Porcelain  . 

.  37-41 

Brick-earth  . 

•  36-37 

30*38 

17-96 

2'34 

I  "22 

II3 


The  metals  are  evidently  the  best  conductors ;  but  even  these  differ  remark¬ 
ably,  gold  being  too,  whilst  lead  has  not  one-fifth  of  the  conducting  property 
and  power  of  transmitting  molecular  motion  possessed  by  the  first-named 
metal.  Brick-earth  is  constituted  of  a  number  of  distinct  bodies;  it  is  a 
mechanical  mixture  of  a  variety  of  compounds,  each  of  which  has  an  exact 
chemical  composition.  The  particles  are  not  only  different  from  each  other, 
but  are  widely  apart ;  the  substance  is  of  a  porous  nature.  Asbestos,  pumice- 
stone,  charcoal — and  especially  animal  charcoal — sand,  are  all  porous,  and 
well-known  bad  conductors,  so  much  so  that  a  red-hot  ball  of  iron  can  be 
held  in  the  hand  for  a  certain  time,  provided  a  layer  of  either  of  the  above- 
named  substances  intervene  between  the  skin  of  the  hand  and  the  heated 
metal. 

By  a  more  careful  mode  of  experimenting,  the  conductivity  of  the  various 
metals  has  been  determined  by  Despretz,  Wiedemann,  and  Franz.  In  this 
table  it  will  be  seen  that  silver  occupies  the  first  place,  instead  of  gold,  which 
is  third.  Platinum,  again,  which  stands  second  in  the  first  table,  is  very  low 
down  in  the  scale  of  conductivity;  and  bismuth  i;  the  lowest  of  all. 


CONDUCTION. 


i?  7 


Silver 

* 

• 

.  100 

Iron  . 

12 

Copper 

• 

• 

•  74 

Lead 

9 

Gold 

# 

•  S3 

Platinum  . 

8 

brass 

•  24 

German  silver  . 

6 

Tin  . 

• 

• 

•  15 

Bismuth  . 

2 

Franklin  and  Igenhausz  must  therefore  have  committed  some  gross  errors 
in  their  experiments,  or  the  second  table  quoted  here  is  wrong. 

Dr.  Tyndall  explains  the  cause  of  the  difference  with  a  very  pretty  experi¬ 
ment.  He  takes  a  short  prism  of  bismuth,  and  another  of  iron,  of  the  same 
size,  and  having  coated  the  extremities  with  wax,  they  are  both  placed  on  the 
lid  of  a  vessel  filled  with  boiling  water.  Strange  to  say,  the  wax  on  the 
bismuth  melts  first ,  although  it  has  six  times  less  conductivity  than  iron. 
Here  is  a  paradox  which  requires  explanation,  and  shows  why  the  experiments 
conducted  by  Franklin  and  Igenhausz  cannot  agree  with  those  of  more 
modern  physicists.  In  the  first  place,  the  test  of  conductivity  employed  by 
the  earlier  experimenters  was  the  rapidity  with  which  the  wax  and  tallow 
coating  a  bar  of  any  given  substance  melted  in  comparison  with  another — 
just  as  Tyndall  used  the  prisms  of  bismuth  and  iron. 

In  the  second  place,  the  mode  of  experimenting  employed  by  Despretz 
was  not  simply  a  determination  of  the  rapidity  with  which  the  thermometer 
inserted  in  the  bar  was  affected,  as  shown  in 


a  b  c  d  •  f 


Fig.  160. — Despretds  Mode  of  determining  the  Conductivity  of  Metals; 

a,  the  bar  containing  the  thermometers,  a,  h,  c,  d,  e,/-,  b,  glass  snpportingA  j  d,  the  spint-lamp. 


but  he  waited  until  the  bar  showed  a  stationary  condition  of  heat,  and  the 
thermometers  no  longer  continued  to  rise,  and,  by  estimating  the  difference 
between  each  thermometer,  he  soon  discovered  that  the  best  conductors 
produced  the  least  amount  of  difference  between  the  thermometers,  and  that 
the  worst  conductor  gave  the  contrary  result. 

Why  did  he  wait  until  the  heat  of  the  bar  became  stationary  ? 

To  avoid  the  error  caused  by  the  difference  of  “  specific  heat,  which  varies 
with  every  substance.  This  difference  is  readily  explained  by  the  following 
experiments : 

A  pint  of  water  at  503  F.  mixed  with  a  pint  at  100  t .  will  amount  to  a 
quart,  which  will  have  a  mean  temperature  of  750  h. 


12 


HEAT. 


178 


50°  F. 
1  oo°  F. 


2)150 


75°  F. 


Here  the  molecules  are  exactly  the  same ;  it  is  water  mixed  with  water,  and 
the  particular  heat  required  to  raise  any  given  bulk  to  a  certain  temperature 
cannot  alter.  If,  however,  a  pint  of  water  at  ioo°  F.  is  mixed  with  a  pint  of 
mercury  at  40°  F.,  the  resulting  temperature  is  not  the  mean,  70°,  but  8o°; 
the  water  has  only  fallen  20°,  whilst  the  mercury  has  risen  40°.  The  20°  of 
heat  from  the  water  has  been  sufficient  to  heat  the  mercury  40°.  Hence  it  is 
apparent  that  mercury  has  a  less  “  capacity  for  heat  ”  (keeping  to  old  expres¬ 
sions)  than  water,  and  it  requires  a  smaller  amount  of  heat  to  raise  it  to  a 
given  temperature,  viz.,  8o°.  For  the  term,  “capacity  of  heat,”  or  “specific 
heat,”  substitute,  according  to  the  dynamical  theory,  the  term,  “  power  to 
get  into  molecular  motion,”  or  “  capacity  for  molecular  motion.” 

We  may  once  more  return  to  Tyndall’s  paradox  with  the  bismuth  and  iron. 
The  “capacity  for  heat,”  or  “specific  heat,”  of  iron  is  o-U38;  that  of 
bismuth  is  only  0x1308 :  like  the  mercury  and  the  water  experiment,  it  takes 
less  heat  to  warm  any  given  mass  of  bismuth  than  it  does  to  heat  an  equal 
bulk  of  iron. 

The  molecular  motion  which  can  be  set  up  in  bismuth  occurs  much 
quicker  than  it  does  in  iron  :  one  might  almost  say  that  the  “  inertia  of  heat  ” 
in  iron  was  greater  than  that  of  bismuth.  But  this  inertia  once  overcome, 
and  each  metal  transmitting  all  the  molecular  motion  which  can  be  conferred 
from  the  vessel  containing  the  boiling  water,  it  will  soon  be  found,  according 
to  the  table  quoted  by  Tyndall,  that  iron  transmits  six  times  more  vibratory 
power,  or  motion  of  heat,  than  bismuth ;  it  has  less  power  to  get  into 
molecular  motion  than  bismuth,  but,  once  in  motion,  it  sends  vibration  after 
vibration  from  molecule  to  molecule,  and  soon  outstrips  the  bismuth  in  the 
race  of  conductivity. 

In  this  place  it  is  desirable  to  speak  of  certain  terms  which  have  arisen 
and  are  used  in  conformity  with  the  dynamical  theory  of  heat. 

1. — “Potential”  Force. 

Potential  force  may  be  defined  as  a  power  waiting  and  ready  to  be  used; 
“the  sword  of  Damocles  suspended  by  a  hair;”  the  giant  standing  jnotion- 
less,  but  capable,  at  the  word  of  command,  of  exerting  great  physical  power. 
It  is,  in  short,  stored-up  energy — the  gold  in  the  bank  cellars,  potential,  but 
not  in  circulation  or  use.  Substitute  for  the  word  “  force”  heat,  and  you  have 
potential  heat. 

2. — “Actual”  Force,  or  “Energy.” 

As  the  first  was  dormant  or  passive,  the  second  is  “  actual  ”  or  real,  and 
makes  itself  apparent — the  hair  broken,  the  sword  in  the  act  of  descending. 
They  are  mutually  convertible  :  as  actual  heat  appears,  potential  heat  is  used 
up  and  disappears.  You  cannot  store  gold  in  a  cellar  and  use  it  at  the  same 
time. 

The  stored  gold  would  represent  potential  heat  ;  the  gold  in  use  or  circular 


CONDUCTION. 


179 


tion,  actual  heat.  A  country  in  a  state  of  peace  would  have  gold  stored,  and 
ready  to  pay  an  army  ;  but  the  latter,  once  formed  and  in  actual  service,  must 
be  paid  ;  and  as  the  army  becomes  active,  the  potential  energy — the  gold — 

disappears. 

One  pound  of  hydrogen  and  eight  pounds  of  oxygen  contain  potential 
energy  which  is  enormous  ;  when  they  unite,  they  form  nine  pounds  of  water, 
and  the  mechanical  value  of  the  heat,  or  actual  energy,  set  free  is  equivalent 
to  a  force  that  would  raise  forty-seven  millions  of  pounds  weight  one  'foot 

high. 

The  change  of  one  pound  of  hydrogen,  by  combination  with  eight  pounds  of 
oxygen,  into  nine  pounds  of  water  would  be  an  example  of  “chemical  action.” 

Action  and  reaction  are  equal,  but  contrary ;  and  therefore  Dr.  Odling’s 
admirable  lecture  “  On  Reverse  Chemical  Action,”  delivered  before  the  last 


Fig.  161. 


A.  the  tlaskof  water  boiled  by  spirit-lamp,  and  delivering  steam  to  the  platinum  tuben,  coiled  round  and 
placed  in  a  hollow  made  in  a  firebnck,  and  subjected  to  the  intense  heat  of  the  oxy-hydrogen  blow, 
pipe  c.  d,  small  pneumatic  trough  and  tube  for  collection  of  the  two  gases,  oxygen  and  hydrogen. 

meeting  of  the  British  Association,  held  at  Norwich,  is  most  welcome,  because 
it  supplies  the  reasoning  for  the  opposite  effect — viz.,  the  conversion  of  “actual 
energy,  or  heat,”  into  potential  energy. 

By  passing  the  vapour  of  water  through  a  spiral  platinum  tube,  made  white- 
hot  by  the  oxy-hydrogen  flame,  the  vapour  is  divided  again  into  its  elements, 
oxygen  and  hydrogen.  This  beautiful  experiment,  so  worthy  of  the  author  of 
the  “  Correlation  of  the  Physical  Forces,”  Professor  Groves,  is  shown  at  Fig. 
161. 

The  platinum  tube  has  no  power  to  unite  with  the  oxygen  or  the  hydrogen ; 
it  is  simply  the  vehicle  for  the  application  of  the  intense  heat  of  the  oxy- 
hydrogen  blowpipe.  The  potential  energy  of  the  mixed  gases  produces  actual 
energy  or  heat,  and  the  latter  again  stores  up  potential  energy  by  the  repro¬ 
duction  of  hydrogen  and  oxygen.  Nothing  can  be  more  perfect  as  a  train  of 
experimental  reasoning,  or  more  decidedly  illustrate  the  conversion  of  poten¬ 
tial  into  actual  energy,  and  vice  versd.  It  is  a  true  illustration  of  “conserva¬ 
tion  of  energy,”  and  enables  the  student  to  realise  the  magnificent  principle 
•which  destroys  nothing,  nor  admits  thedestruction  of  anything,  because  through¬ 
out  the  universe  the  sum  of  these  two  energies,  called  “  potential  ”  and 

12—2 


i8o 


HEAT. 


“  actual,”  is  equal.  The  conclusion  of  Dr.  Odling’s  brilliant  address,  “  On 
Reverse  Chemical  Action,”  admirably  expresses  these  grand  truths  : 

“  Reverse  chemical  actions  are  those  which  do  not  take  place  of  themselves, 
but  only  by  the  application  of  some  external  force  or  agency,  which  force 
becomes  as  it  were  stored  up  in  the  product  of  the  reaction  ;  in  other  words, 
it  is  attended  by  a  conversion  of  potential  into  actual  energy.  It  is  an  instance 
of  winding  up,  and  not  of  running  down.  Direct  chemical  action  takes  place 
of  itself  by  virtue  not  of  an  innate  tendency  of  the  bodies,  which  acts,  but  of 
an  energy  which  has  been  put  into  the  bodies  at  some  time  or  other ;  it  takes 
place  of  itself,  and  is  attended  by  the  liberation  of  pent-up  forces  contained  in 
the  reacting  bodies, —  in  other  words,  it  is  attended  by  a  conversion  of  potential 
into  actual  energy.  Every  direct  chemical  combination  has  been  preceded 
by  some  reverse  chemical  action,  just  as  the  falling  down  of  a  weight  has  been 
preceded  by  the  winding  of  it  up.  When  we  consume  wood  and  coal  in  our 
fires,  or  bread  and  wine  in  our  bodies,  we  merely  effect  a  combination  whereby 
their  potential  is  converted  into  actual  energy,  this  potential  energy  having 
been  stored  up  in  them  at  the  period  of  their  formation  ;  this  energy  being,  in 
fact,  the  robbing  of  the  sun’s  rays,  and  the  storing  up  the  heat  of  these  rays 
in  these  articles  of  fire  and  fuel.  Under  the  action  of  the  sun’s  rays  the  de¬ 
composition  is  effected  of  the  carbonic  acid  and  water  into  oxygen  gas, 
restored  to  the  atmosphere,  and  carbon-hydrogen,  which  is  accumulated  in 
the  vegetable  tissue.  When  we  burn  these  tissues  in  our  fires  or  bodies,  we 
are  simply  restoring  in  the  form  of  actual  energy  the  potential  heat  of  the 
sun’s  rays  or  its  mechanical  equivalent.  We  have  all  read  of  the  Bourgeois 
Gentilhomme  who  had  been  talking  prose  all  his  life  without  knowing  it.  We 
have  all  our  lives,  and  some  of  us  without  knowing  it,  been  realising  that 
celebrated  problem  of  extracting  sunbeams  from  cucumbers.” 

It  should  be  mentioned  that  Wiedemann  and  Franz  did  not  employ  ther¬ 
mometers  ;  they  used  a  more  refined  arrangement  with  the  thermo-electric 
pile  and  galvanometer  needle — a  most  delicate  measurer  of  heat,  which  will 
be  more  fully  explained  presently.  Wool,  chalk,  stone,  fire-clay,  ivory,  are 
all  bad  conductors  of  heat.  Asbestos,  powdered  pumice-stone,  charcoal,  saw¬ 
dust,  and  snow  are  still  worse  conductors  of  heat.  The  subdivision  and 
pulverization  of  the  substance  increase  porosity,  and  decrease  conductivity. 
The  wool  and  fur  of  animals,  the  plumage  of  birds,  and  especially  the  down 
(made  into  eider-down  quilts),  are  all  good  examples  of  the  wondrous  care 
with  which  a  superintending  Creator  has  foreseen  the  various  wants  of  the 
animal  kingdom,  and  protected  them  even  against  the  vicissitudes  of  tem¬ 
perature. 

The  kettle-holder  made  of  wool,  the  pieces  of  ivory  which  break  the  metallic 
communication  between  the  good-conducting  silver  teapot  and  its  handle  and 
the  soot — charcoal — covering  the  bottom  of  a  kettle,  which  allows  the  vessel 
to  be  taken  direct  from  the  fire  and,  though  full  of  boiling  water,  held  upon 
the  palm  of  the  hand,  are  good  and  familiar  examples  of  the  application  of 
bad  conductors. 

One  of  the  most  interesting  novelties  displayed  in  the  department  devoted 
to  Norway,  in  the  French  Exhibition  of  1867,  was  the  Self-acting  Norwegian 
Cooking  Apparatus,  constructed  in  the  most  simple  manner,  of  a  wooden  box 
lined  with  four  inches  of  felt,  in  which  the  saucepans  containing  the  food, 
previously  boiled  and  maintained  at  the  boiling-point  for  five  or  ten  minutes, 
according  to  the  nature  of  the  food  to  be  cooked,  are  placed.  The  heated 


CONDUCTION. 


181 


saucepans  are  covered  with  a  thick  felt  cover,  and,  the  lid  of  the  box  being 
fastened  down,  the  rest  of  the  cooking  is  done  by  slow  digestion,  no  more  heat 
being  added. 

The  heated  vessels  containing  the  food  will  retain  a  high  temperature  for 
several  hours,  so  that  a  dinner  put  into  the  apparatus  at  8  in  the  morning 
would  be  quite  hot  and  ready  by  5  in  the  afternoon,  and  would  keep  hot  up 
to  10  or  12  at  night,  because  the  felt  clothing  so  completely  prevents  the 
escape  of  the  heat ;  and  as  the  whole  is  enclosed  in  a  box,  there  are  no  currents 
of  air  to  carry  off  any  other  heat  by  convection. 


Fig.  162. — The  Norwegian  Self-Acting  Cooking  Apparatus. 

A,  the  box,  lined  with  felt ;  b  b,  saucepans  fitting  into  box;  c,  the  felt  cover  to  be  placed  on  the 

top  of  the  saucepans. 


The  principle  on  which  this  cooking  apparatus  acts  is  that  of  retaining  the 
heat;  and  it  consists  of  a  heat-retainer  or  isolating  apparatus  shaped  somewhat 
like  a  refrigerator,  and  of  one  or  more  saucepans  or  other  cooking-vessels 
made  to  fit  into  it.  Whereas  in  the  ordinary  way  of  cooking  the  fire  is  neces¬ 
sarily  kept  up  during  the  whole  of  the  time  required  for  completing  the  cooking 
process,  the  same  result  is  obtained,  in  using  this  apparatus,  bv  simply  giving 
the  food  a  start  of  a  few  minutes’  boiling,  the  rest  of  the  cooking  being  com¬ 
pleted  by  itself  in  the  heat-retainer  away  from  the  fire  altogether. 

Directions  for  use. — Put  the  food  intended  for  cooking,  with  the  water  or 
other  fluid  cold,  into  the  saucepan,  and  place  it  on  the  fire.  Make  it  boil,  and 
when  on  the  point  of  boiling  skim  if  required.  This  done,  replace  the  lid  of 
the  saucepan  firmly,  and  let  it  continue  boiling  for  a  few  minutes.  After  the 
expiration  of  these  few  minutes,  take  the  saucepan  off  the  fire,  and  place  it 
immediately  into  the  isolating  apparatus,  cover  it  carefully  with  the  cushion, 
and  fasten  the  lid  of  the  apparatus  firmly  down.  In  this  state  the  cooking 
process  will  complete  itself  without  fail. 

By  no  means  let  the  apparatus  be  opened  during  the  time  required  for 
cooking  the  food. — The  length  of  time  which  the  different  dishes  should  remain 
in  the  isolating  apparatus  varies  according  to  their  nature.  It  may,  however, 
be  taken  as  a  general  rule  that  the  same  time  is  required  to  complete  the 
cooking  in  the  apparatus  as  in  the  ordinary  way  on  a  slow  fire. 

The  advantages  of  this  apparatus  are  thus  detailed  by  Herr  Sorensen,  the 
patentee,  whose  attention  was  first  directed  to  the  subject  by  the  Norwegian 


182 


HEAT. 


peasants,  who  heat  their  food  in  the  morning,  and  whilst  away  in  the  fields 
keep  the  saucepan  hot  by  surrounding  it  with  chopped  hay : 

1.  Economy  of  Fuel  varies  according  to  the  length  of  time  required  for 
cooking  the  different  sorts  of  food.  For  those  requiring,  in  the  ordinary  way, 
only  one  hour’s  cooking,  the  saving  is  about  40  per  cent.  ;  two  hours,  60  per 
cent.  ;  three  hours,  65  per  cent.  ;  six  hours,  70  per  cent.  In  the  case  of  gas 
being  used,  the  saving  would  be  greater  still. 

2.  Economy  of  Labour. — A  few  minutes’  boiling  is  sufficient.  No  fire  is 
necessary  afterwards.  The  cooking-pot  once  in  the  apparatus,  the  cooking 
will  complete  itself.  Over-cooking  is  simply  impossible,  and  the  process  of 
cooking  is  infallible  in  its  result.  The  food  will  be  cooked  in  about  the  same 
time  as  if  fire  had  been  continuously  used.  But  the  food  need  not  be  eaten 
for  many  hours  after  the  cooking  process  is  complete ;  so  that  half-an-hour’s 
use  of  a  fire  on  a  Saturday  night,  for  example,  will  give  a  smoking  hot  dinner 
on  Sunday. 

3.  Portability. — The  weight  of  the  apparatus  complete  varies  from  18  to 
50  lbs.  The  apparatus  can,  in  proportion  to  its  dimensions,  be  carried  about 
with  great  facility,  without  interfering  with  the  cooking  process.  By  means 
of  a  large  apparatus — for  instance,  following  on  a  cart  a  detachment  of  soldiers 
on  the  march — it  is  possible  to  provide  them  with  a  hot  meal  at  any  moment 
it  might  be  found  convenient  (as  may  be  proved  by  official  reports  from  the 
officers  of  the  Royal  Guard  at  Stockholm,  in  the  possession  of  the  patentee). 

Again,  fishermen,  pilots,  and  others  whose  small  vessels  are  not  generally 
so  constructed  as  to  enable  them  to  procure  hot  food  while  at  sea,  may  easily 
do  so,  by  taking  out  with  them  in  the  morning  an  apparatus  prepared  before 
their  departure.  It  is,  in  short,  a  thing  for  the  million,  for  rich  and  poor ;  for 
the  domestic  kitchen,  as  well  as  for  persons  away  from  their  homes.  It  cooks, 
and  keeps  food  hot,  just  as  well  when  carried  about  on  a  pack-saddle,  on  a 
cart,  or  in  a  fisherman’s  boat,  as  in  a  coal-pit  or  under  the  kitchen  table. 

4.  Quality  and  quantity  of  the  food  prepared. — Where  other  plans  of  cook¬ 
ing  waste  one  pound  of  meat,  this  apparatus,  properly  used,  wastes  about  one 
ounce.  The  unanimous  testimony  of  those  who  have  used  it  pronounces  the 
flavour  of  food  cooked  in  this  manner  incomparably  superior  to  that  which  is 
ordinarily  produced. 

5.  Simplicity  of  use. — One  of  the  greatest  advantages  of  this  invention  is, 
no  doubt,  its  simplicity  and  practical  application.  There  is  no  complication 
of  hot-water  or  air  pipes  to  retain  the  heat,  no  mechanical  combination  what¬ 
ever  for  producing  a  high  degree  of  heat  by  steam  pressure  ;  consequently 
there  is  no  necessity  for  steam-valves  or  other  combinations  which  would 
render  the  use  of  the  apparatus  difficult  and  dangerous.  Any  person  will, 
without  difficulty,  be  able  to  use  the  apparatus  to  advantage  after  once  having 
witnessed  it  in  operation.  No  special  arrangement  is  required  in  the  kitchen 
for  using  the  apparatus.  Any  fuel  will  do  for  starting  the  cooking. 

6.  In  addition  to  all  these  advantages,  the  complete  apparatus  constitutes 
the  ‘  Simple  Refrigerator’  for  the  preservation  of  ice,  which  has  attracted  so 
much  notice  (see  Letters  in  Times ,  July  30,  31,  August  4,  1868),  and  had  such 
warm  approval  from  medical  men.  It  will  keep  ice  in  small  quantities  for 
many  days. 

In  the  organization  of  our  bodies  there  are  chemical  changes  going  on 
which  maintain  a  certain  temperature.  It  matters  not  whether  the  living 
being,  man,  is  a  resident  of  tropical  or  polar  regions ;  the  temperature  required 


CONDUCTION. 


183 


to  promote  and  carry  on  vitality  remains  the  same,  or  nearly  so.  If  the  cold  or 
absence  of  heat  is  likely  to  be  dangerous,  man  uses  the  skins  and  furs  of 
animals  for  his  clothing,  and  takes  care  to  lose  little  or  no  heat.  On  the 
other  hand,  if  the  heat  is  excessive,  increased  action  of  certain  powers  throws 
out  perspiration,  which  carries  off  the  heat  that  might  accumulate  and  prove 
dangerous.  Solid  bodies  convey  their  heat  rapidly  to  the  human  body,  and 
the  reverse.  Somebody  said  that  a  frog  could  not  be  killed  by  any  extreme 
of  cold  ;  but  when  the  animal  was  carefully  dressed  in  tinfoil  and  then  sub¬ 
jected  to  the  cold  produced  by  a  freezing  mixture,  the  conducting  power  of  the 
metal  was  too  much  for  the  animal  powers  of  the  frog  to  resist,  and  he  was 
killed.  The  air  during  the  summer  months  is  often  very  hot — upwards  of 
ioo°  F.  in  the  glare  of  the  sunlight  ;  but  the  heat  from  air  is  very  slowly  com¬ 
municated  to  the  body,  and  the  latter  has  time  to  neutralize  the  otherwise 
burning  ‘heat  by  consuming  it  in  work,  i.  e.,  by  forcing  water  through  the 
pores  of  the  skin,  and  converting  it  in  part  into  vapour. 

The  very  low  conductivity  of  the  gases  is  shown  by  some  very  interesting 
experiments,  performed  by  Tillet  in  France,  and  by  Dr.  Fordyce  and  Sir 
Charles  Blagdcn  and  others  in  England,  and  thus  related  by  Sir  David 
Brewster  in  his  charming  little  book  called  “  Letters  on  Natural  Magic:” 

“Sir  Charles  Blagden,  Dr.  Solander,  and  Sir  Joseph  Banks  entered  a  room 
in  which  the  air  had  a  temperature  of  198°  F.,  and 'remained  ten  minutes;  but, 
as  the  thermometer  sank  very  rapidly,  they  resolved  to  enter  the  room  singly. 
Dr.  Solander  went  in  alone,  and  found  the  heat  210°  F.,  and  Sir  Joseph  entered 
when  the  heat  was  21 1°  F.  Though  exposed  to  such  an  elevated  temperature, 
their  bodies  preserved  their  natural  degree  of  heat.  Whenever  they  breathed 
upon  a  thermometer,  it  sank  several  degrees:  every  expiration,  particularly 
if  strongly  made,  gave  a  pleasant  impression  of  coolness  to  their  nostrils,  and 
their  cold  breath  cooled  their  fingers  whenever  it  reached  them. 

“  On  touching  his  side,  Sir  Charles  Blagden  found  it  cold  like  a  corpse ;  and 
yet  the  heat  of  his  body,  under  his  tongue,  was  98°  F. 

“  Hence  they  concluded  that  the  human  body  possesses  the  power  of  destroy¬ 
ing  a  certain  degree  of  heat  when  communicated  with  a  certain  degree  of 
quickness.  This  power,  however,  they  concluded,  varied  in  various  media. 

“The  same  person  who  experienced  no  inconvenience  from  air  heated  to 
2110  could  just  bear  rectified  spirits  of  wine  at  1 30°,  cooling  oil  at  1 29°,  cooling 
water  at  1 23%  and  cooling  quicksilver  at  1 1 70.  A  familiar  instance  of  this 
occurred  in  the  heated  room.  All  the  pieces  of  metal  there,  even  their  watch- 
chains,  felt  so  hot  that  they  could  scarcely  bear  to  touch  them  for  a  moment, 
while  the  air  from  which  the  metal  had  derived  all  its  heat  was  only  unpleasant. 

“  Messrs.  Duhamel  and  Tillet  observed,  in  France,  that  the  girls  who  were 
accustomed  to  attend  ovens  in  a  bakehouse  were  capable  of  enduring  for  ten 
minutes  a  temperature  of  270°. 

“  The  same  gentlemen  who  performed  the  experiments  above  described 
ventured  to  expose  themselves  to  a  still  higher  temperature. 

“  Sir  Charles  Blagden  went  into  a  room  where  the  heat  was  1  or  2  above 
260°  F.,  and  remained  eight  minutes  in  this  situation,  frequently  walking  about 
to  all  the  different  parts  of  the  room,  but  standing  still  most  of  the  time  in 
the  coolest  spot,  w  here  the  heat  was  above  240’  f . 

“The  air,  though  very  hot,  gave  no  pain,  and  Sir  Charles  and  all  the  other 
gentlemen  were  of  opinion  that  they  could  have  supported  a  much  greater 
heat. 


184 


HEAT. 


“  During  seven  minutes  Sir  C.  Blagden’s  breathing  remained  perfectly  good; 
but  after  that  time  he  felt  an  oppression  in  his  lungs,  with  a  sense  of  anxiety, 
which  induced  him  to  leave  the  room.  His  pulse  was  then  144— double  its 
ordinary  quickness. 

“  In  order  to  prove  that  there  was  no  mistake  respecting  the  degree  of  heat 
indicated  by  the  thermometer,  and  that  the  air  which  they  breathed  was  ca¬ 
pable  of  producing  all  the  well-known  effects  of  such  a  heat  on  inanimate 
matter,  they  placed  some  eggs  and  a  beef-steak  upon  a  tin  frame,  near  the 
thermometer,  but  more  distant  from  the  furnace  than  from  the  wall  of  the 
room.  In  the  space  of  twenty  minutes  the  eggs  were  roasted  hard  ;  and  in 
forty-seven- minutes  the  steak  was  not  only  dressed,  but  almost  dry.  Another 
beef-steak  similarly  placed  was  rather  over-done  in  thirty-three  minutes.  In 
the  evening,  when  the  heat  was  still  more  elevated,  a  third  beef-steak  was  laid 
in  the  same  place,  and,  as  they  had  noticed  that  the  effect  of  the  hot  air  was 
greatly  increased  by  putting  it  in  motion,  they  blew  upon  the  steak  with  a  pair 
of  bellows,  and  thus  hastened  the  cooking  of  it  to  such  a  degree  that  the 
greatest  portion  of  it  was  found  to  be  pretty  well  done  in  thirteen  minutes. 

“  Sir  Francis  Chantrey,  the  late  eminent  sculptor,  exposed  himself  to  a  tem¬ 
perature  still  higher  than  any  yet  mentioned. 

“The  furnace  he  employed  for  drying  his  moulds  was  about  14  ft.  long, 
12  ft.  high,  and  12  ft.  broach  When  raised  to  its  highest  temperature  with  the 
doors  closed,  the  thermometer  stood  at  350°  F.,  and  the  iron  floor  was  red  hot. 
The  workmen  entered  it  at  a  temperature  of  340",  walking  over  the  iron  floor 
with  wooden  clogs  which  had  become  charred  on  the  surface.  On  one  occasion 
Sir  Francis,  accompanied  by  five  or  six  of  his  friends,  entered  the  furnace,  and, 
after  remaining  two  minutes,  they  brought  out  a  thermometer  which  stood  at 
320°.  Some  of  the  party  experienced  sharp  pains  in  the  tips  of  their  ears  and 
in  the  septum  of  the  nose,  while  others  felt  a  pain  in  their  eyes.” 

In  this  very  interesting  account  we  see  it  was  assumed  by  the  observers  that 
the  power  of  resisting  the  high  temperature  was  due  to  some  natural  power  or 
vitality,  and  yet  it  is  stated  that  the  tips  of  the  ears  and  the  septa  of  the  nose 
were  painfully  affected.  Certainly  a  live  body  resists  a  heat  that  would  cook 
a  dead  one;  therefore,  in  the  abstract,  vitality  or  the  maintenance  of  the 
various  processes  inseparable  from  the  living  being,  must  not  be  wholly  dis¬ 
regarded,  as  without  vitality  none  of  those  changes  of  matter  could  occur  which 
enable  the  living  tissues  to  resist  the  great  heat;  but,  after  all,  the  “actual” 
heat  is  converted  into  “  potential  ”  heat,  perspiration  is  secreted  and  escapes 
from  the  natural  outlets  of  the  body,  the  pores  of  the  skin,  and  the  lungs. 
Time,  of  course,  is  an  important  element  in  these  experiments,  and  even  the 
living  body  must  succumb  to  any  lengthened  application  of  the  great  heat 
already  described. 

Heated  gases  impart  their  heat  very  slowly  to  surrounding  objects,  because 
the  gases  are  bad  conductors  of  heat.  If,  for  the  sake  of  discussion,  we  could 
imagine  an  atmosphere  composed  of  minute  and  rare  atoms  of  silver,  such  an 
atmosphere,  if  it  could  be  breathed,  would  impart  its  heat  with  dangerous 
rapidity  to  the  body 

Liquids,  like  gases,  conduct  heat  very  slowly.  The  hand  may  be  placed 
within  a  short  distance  of  a  quantity  of  boiling  water,  and  is  wholly  unaffected 
by  its  dangerous  neighbour.  The  author  devised  and  arranged  the  experiment 
by  first  placing  round  a  cylindrical  glass,  that  will  easily  admit  the  hand,  a 
large  tube  of  caoutchouc. 


CONDUCTION. 


185 


The  large  tube  can  be  made  in  the  usual  manner,  by  cutting  the  edges  of 
the  sheet  of  caoutchouc  first,  and  then  winding  it  twice  or  thrice  round  some 
cylindrical  vessel ;  the  whole,  being  kept  together  with  tape,  is  then  boiled  and 
allowed  to  cool;  a  large  india-rubber  tube  is  then  obtained,  which  can  be 
stretched  over  one  end  of  the  glass  cylinder  and  properly  fixed  with  string; 
the  hand  is  then  inserted,  and  the  india-rubber  tube  tied  round  the  wrist. 

The  glass,  containing  the  hand,  is  now  held  upright,  and  cold  water  poured 
in,  so  that  the  clenched  hand  is  covered  with  one  inch  of  water.  Some  boiling 


Fig.  163. —  The  Hand  placed  in  Water  which  is  boiling  above  it. 

A,  section  of  glass  cylinder,  made  a  little  funnel-shaped  at  the  top,  with  the  caoutchouc  tube  r  b  attached 
by  string  to  the  lower  part;  c  c»  apparatus  attached  to  the  arm,  and  tied  round  tightly,  so  that  the 
water  cannot  escape  :  this  must  be  carefully  attended  to,  because  if  the  cold  water  run**  away  the 
boiling  water  will  come  down  upon  and  scald  the  hand  ;  d,  the  red  hot  iron  (the  half  of  a  dumb-bell 
with  a  hole  bored  through  it)  held  by  a  hook. 


water,  coloured  with  a  solution  of  indigo,  is  now  carefully  poured  in  down  the 
sides  of  the  glass,  or,  better  still,  on  a  thin  disc  of  cork,  floating  on  the  cold 
water  above  the  hand.  The  line  of  demarcation  is  readily  seen  by  the  differ¬ 
ence  between  the  colourless  cold  and  the  coloured  hot  water.  A  red-hot  ball, 
held  by  a  hooked  iron,  is  now  applied  to  the  top  of  the  coloured  water,  which 
will  soon  enter  into  a  violent  state  of  ebullition  :  the  water  boils  at  the  top,  but 
does  not  communicate  its  heat  by  conduction  downwards  to  the  hand. 

After  the  experiment  has  been  tried,  of  course  the  arm  must  not  be  reversed 
to  pour  out  the  water,  or  else  the  hand  may  be  scalded.  A  syphon,  protected 
by  a  fold  of  flannel  or  paper,  may  be  filled  with  cold  water  in  the  usual  way, 


i86 


HEAT. 


and  the  boiling  water  run  off  quickly.  If  the  syphon  was  not  covered  with 
some  bad  conducting  substance,  the  person  helping  to  run  off  the  boiling 
water  might  be  inclined  to  leave  go.  when  the  hand  inside  would  run  a  great 
risk  of  feeling  the  temperature  of  boiling  water.  It  is,  of  course,  one  of  those 
experiments  which  succeed  thoroughly  if  all  the  manipulations  are  properly 
carried  out  from  the  beginning  to  the  end.  Another  and  very  delicate  proof 
of  the  bad  conductivity  of  water  can  be  shown  by  fixing  a  differential  ther¬ 
mometer  in  a  cork  placed  in  the  mouth  of  an  inverted  gas  jar,  and  then  heat¬ 
ing  the  water  at  the  top  with  a  red-hot  iron. 

Although  the  thermometer  is  unaffected,  it 
does  not  follow  that  water  will  not  conduct 
heat.  M.  Despretz  has  ascertained  that  water 
will  conduct  heat  very  slowly.  The  motion  of 
the  particles  which  is  immediately  set  up  when 
the  water  is  heated  from  the  top  must  tend 
to  destroy  that  similarity  of  molecules  which 
seems  so  desirable  to  secure  good  conducti¬ 
vity.  Directly  any  portion  of  the  water  is 
heated,  its  gravity  is  altered,  and  it  becomes 
lighter;  this  perpetual  motion  of  the  indivi¬ 
dual  particles  must  interfere  with  the  steady 
propagation  of  dynamical  force,  which  has 
been  shown  to  be  essential  to  good  conducti¬ 
vity.  It  appears  to  be  doubtful  whether  gases 
do  conduct  heat :  the  molecules  are  too  wide 
apart,  and  have  greater  mobility  than  liquids. 

Both  with  liquids  and  gases,  circulation  is  a 
necessary  condition  if  either  are  to  be  warmed, 
and  hence,  in  speaking  of  the  application  of 
heat  to  these  forms  of  material  substances, 
another  term  is  employed,  viz.,  “  convection,” 
or  carrying  power.  To  heat  a  vessel  of  water 
to  the  boiling-point,  the  tire  must  be  applied  at 

the  bottom;  a  circulation  of  particles  immediately  commences;  the  expanded 
or  lighter  particles  rise  by  reduced  specific  gravity  to  the  top,  and,  as  they  travel 
upwards,  convey  the  heat  “by  convection”  through  the  other  and  colder  particles, 
which  descend  to  take  their  place,  and  thus  a  constant  circulation  is  set  up 
until  the  whole  is  brought  to  one  temperature,  viz.,  the  boiling-point,  2i2°  F. 
When  Sir  Joseph  Banksand  others  experimented  with  the  atmosphere  heated 
to  260°,  they  found  that  if  the  heated  air  was  set  in  motion  and  caused  to  travel 
rapidly,  with  the  aid  of  the  bellows,  over  the  skin,  the  heat  soon  became  dis¬ 
agreeable,  and  with  dead  matter  (the  beef-steak),  at  a  higher  temperature,  it 
was  distinctly  shown  that  the  process  of  cooking  was  more  rapidly  carried  on 
when  the  hot  air  was  kept  is  motion  and  its  carrying  power  made  use  of.  I'he 
same  fact  was  observed  by  the  Arctic  discoverers,  who  could  bear  the  most 
intense  cold,  viz.,  minus  55°,  or  140  below  the  freezing-point  of  mercury',  when 
the  air  was  still ;  but,  if  set  in  motion,  the  wind,  the  current  of  air,  or  the  cold 
blast  dangerously  affected  the  extremities,  which  were  rapidly  deprived  of  heat 
by  this  power  of  convection,  and  frozen  or  “frost-bitten.” 

Whilst  travelling  in  Canada,  the  writer  was  informed  by  Mr.  F.  H  Andrews, 
of  Montreal,  that  he  had  experienced  intense  cold  in  that  part  of  America,  the 
thermometer  being  42°  below  zero,  and  his  statement  is  as  follows; 


Fig.  164. 


A  A,  inverted  gas  jar  with  neck  c  stopped 
with  a  good  cork,  through  which  the 
stem  attached  to  the  differential  ther¬ 
mometer  B  u  passes.  The  jar  is  filled 
with  cold  water  and  heated  from  the 
top  by  a  common  urn-heater,  D. 


CONDUCTION. 


187 


“  In  1823  I  was  assistant  in  the  Royal  Grammar  School  at  Montreal,  under 
Alexander  Skakel,  M.A.,  LL.D.  On  January  28th,  Mr.  Skakel — having  ob¬ 
served  on  the  previous  night  the  thermometer  was  very  low  —looked  at  his 
thermometer  early  in  the  morning,  and  found  that  the  mercury  had  shrunk 
entirely  into  the  bulb.  He  then  referred  to  his  spirit  thermometer,  and  found 
that  it  ind  cated  420  below  zero.  He  sent  upstairs  to  myself  and  Messrs. 
McDonald  and  Randal  (the  other  teachers  sleeping  in  the  house),  and  in¬ 
formed  us  that  he  purposed  breaking  one  of  his  mercurial  thermometers,  that 
he  might  say  he  had  handled  solid  me<cury.  We  all  descended  to  a  back 
gallery,  on  which  he  broke  one,  and  the  mercury  rolled  away  like  a  marble. 
Mr.  Skakel  took  it  up,  and  afterwards  gave  it  to  each  one  of  us  to  handle. 
There  was  not  a  breath  of  wind,  and  1  walked  the  whole  length  of  Little 
St.  James  Street  without  feeling  the  weather  to  be  otherwise  than  moderately 
cold. 

“  Montreal,  Jan.  28th,  1873.  “(Signed),  “  F.  H.  Andrews.” 

In  all  schemes  for  ventilating  and  supplying  heated  air,  circulation  must,  of 
course,  be  maintained,  either  to  impart  or  carry  off  heat. 

It  is  said  that,  if  the  hand  is  kept  perfectly  still  in  water  heated  to  a  tempera¬ 
ture  of  1 50°  F.,  the  nerves  are  not  disagreeably  affected  ;  but  directly  the  hand 
is  moved,  then  the  heat  becomes  painful,  and  cannot  be  borne. 

As  an  illustration  of  convection,  or  the  carrying  of  heat,  on  the  grand  scale, 
there  are  the  trade  winds  and  the  Gulf  Stream. 

In  the  tropics  the  heated  earth  imparts  some  of  its  force  to  great  volumes 
of  air,  which  ascend  and  flow  towards  the  poles;  upper  currents  from  the 
equator  to  the  poles  must  be  succeeded  by  under  currents  from  the  poles  to 
the  equator. 

The  constantly  ascending  warm  air  is  thus  a  carrier  of  heat  to  colder  cli¬ 
mates,  and  vice  versa.  These  currents  are  modified  by  the  various  physical 
conditions  of  the  earth’s  surface. 

In  like  manner,  a  great  current  of  warm  water,  which  leaves  the  Straits  of 
Florida  at  a  temperature  of  83°  F.,  passes  across  the  Atlantic  in  a  north¬ 
easterly  direction.  It  washes  the  north-western  shores  of  Europe,  and  makes 
itself,  or  rather  its  heat-giving  power,  apparent  by  flowing  round  the  coast  of 
Ireland.  In  mild  winters  in  England  it  is  the  diffusion  of  heat  by  certain 
winds,  and  the  good  offices  of  the  Gulf  Stream,  which  mitigate  the  severity 
of  the  season  ;  and  these  carriers  of  heat  are  only  neutralized  when  similarly, 
but  contrarily,  enormous  masses  of  ice,  icebergs,  are  detached  from  the  polar 
regions,  and  rob  the  water  of  its  heat  on  its  journey  to  our  shores. 


LATENT  HEAT. 

Capacity  for  Heat — Specific  Heat — Heat  of  Atoms — Atomic  Heat. 

These  somewhat  difficult  terms  or  titles,  referring  to  truths  that  the  \oun^ 
student  does  not,  perhaps,  fully  appreciate  at  first,  nay,  to  speak  plainer, 
which  he  never  will  comprehend  without  industrious  application  to  study, 
are  set  forth  in  the  following  chapters. 

In  all  the  old  standard  works  upon  natural  philosophy  it  is  usual  to  state 
that  there  are  two  kinds  of  heat  that  may  be  resident  in  a  body,  viz.,  one  kind 


i88 


HEAT. 


called  “  sensible  beat,”  which  is  designated  as  temperature,  and  is  capable 
of  measurement  by  the  thermometer  and  other  kindred  in.trummts  ;  another 
and  more  subtle  condition,  not  apparent  to  our  nervous  system,  called  “  latent 
heat,”  and  incapable,  whilst  in  that  condition,  of  affecting  any  measurer  or 
test  of  “  sensible  heat.”  The  dynamical  theory  substitutes  the  terms  “actual 
energy,”  or  force,  for  that  of  “  sensible  heat,”  and  “  potential  energy  ”  for  that 
of  “  latent  heat.” 

The  one,  actual  heat  or  energy,  is  in  use ;  the  other,  potential  heat  or  energy, 
is  in  store.  A  horse-shoe  nail  may  be  warmed  by  any  convenient  source  of 
heat,  and  as  long  as  it  remains  above  the  temperature  of  the  air  we  have 
evidence  of  “  actual  heat.” 

When  cold  it  may  be  hammered  on  an  anvil,  by  an  expert  blacksmith,  and 
then  becomes  so  hot  it  will  set  fire  to  sulphur  or  phosphorus.  The  heat  thus 
evoked  was  formerly  called  “  latent  heat,”  and  was  supposed  to  be  combined 
with  the  material  substance  of  the  iron  ;  the  dynamical  theory  rejects  the 
idea  of  its  being  a  distinct  subtle  fluid,  but  ascribes  the  heat  to  the  motion  ot 
the  particles  of  the  iron.  It  may  be  useful  here  to  tabulate  the  new  terms 
used  by  Clausius,  Rankin,  Tyndall,  and  others,  in  their  exposition  of  the 
dynamical  theory  of  heat. 


Energy  or  Heat. 

Defined  to  be  the  power  of  performing  work.  It  may  be  latent  ox  sensible. 


Latent. 

Possible  energy,  or  work  to  be 
done. 

Potential  energy  is  energy  in  store. 


Sensible. 

Actual  energy,  or  work  is  being 
done. 

Dynamic  energy  is  energy  in  action. 


One  column  of  terms  is  the  exact  antithesis  of  the  other.  There  is  no 
mechanical  machine  by  which  we  can  tear  asunder  or  separate  the  ultimate 
molecules  of  bodies.  Cohesion,  or  molecular  force,  is  too  potent  to  be  over¬ 
come  by  mechanical  energy.  Heat,  another  kind  of  energy,  will,  however, 
act  where  the  former  fails ;  therefore  heat  is  the  equivalent  for  mechanical 
energy. 

When  a  metal  is  expanded  by  heat,  every  molecule  is  separated  or  forced 
asunder;  the  energy  of  heat  must  be  enormous  to  overcome  the  force  of 
cohesion.  When  a  mass  of  metal  is  heated,  there  is  not  only  the  motion 
imparted — the  vibratory  power  set  up  to  produce  sensible  or  actual  energy 
(heat)— but  the  molecules  or  atoms  of  the  metal  are  pushed  asunder,  as 
shown  by  their  expansion.  This  work,  which  goes  on  inside  and  throughout 
the  mass  of  the  metal,  is  not  visible,  and  therefore  may  be  called  “  interior 
work.” 

Tyndall  compares  this  interior  work  to  the  raising  of  a  weight  from  the  earth 
— the  overcoming  of  the  force  of  gravity,  which  attracts  all  things,  and  keeps 
all  terrestrial  bodies  in  their  places.  The  raising  of  a  weight  by  a  cord  from 
the  earth,  it  is  clear,  confers  “  a  motion-producing  power.”  The  weight  can 
fall,  and  in  its  descent  can  perform  work.  Whilst  hanging  in  the  air,  it 
represents  possible  energy,  or  “  potential  ”  energy. 

The  pull,  or  attraction  of  gravity,  causes  this  possible  or  “potential” 
energy.  If  there  were  no  attraction  between  the  substance  and  the  earth, 
there  would  be  no  “possible”  energy. 

Substitute  the  ultimate  atoms  of  bodies  for  the  weight  and  the  earth : 


LATENT  HEAT. 


1S9 


remember  that  the  atoms  of  solid  bodies  are  held  together  with  molecular 
force  (cohesion),  and  it  must  be  evident  that  whenever  they  are  separated, 
although  the  distance  to  which  they  are  separated  cannot  be  measured — it  is 
too  minute — still  the  fact  remains,  and  when  the  atoms  come  together  it  is 
like  the  fall  of  the  weight  to  the  earth,  and  the  result  must  be  the  production 
of  actual  energy,  or  heat. 

This  is  what  Tyndall  means  when  he  speaks  of  the  clashing  together  of 
the  atoms. 

The  heating  of  the  cold  horse-shoe  nail  by  hammering,  or  the  heating  of 
cold  bars  by  rolling,  is  simply  the  conversion  of  mechanical  energy  into 
molecular  motion ;  if  the  approach  of  the  molecules  of  a  body  will  produce 
actual  energy,  a  still  nearer  approach  must  increase  that  energy,  or  heat. 
Indeed,  the  experiment  already  quoted,  of  heat  produced  by  hammering  and 
bringing  the  atoms  nearer  together,  is  a  good  illustration  of  the  above 
argument. 

The  “  specific  heat”  (a  term  that  must  be  carefully  considered  presently)  of 
a  metal  like  copper  is  altered  when  a  nice,  soft,  well-annealed  piece  is  ham¬ 
mered:  heat  is  produced,  and  the  specific  heat  changes  from  0x9501,  0x9455, 
to  0x19360,  0x9330 ;  and  its  specific  gravity  or  density  becomes  higher.  When 
again  heated  red  hot  and  allowed  to  cool  slowly,  as  is  done  in  the  process  of 
annealing,  its  specific  heat  returned  to  0x9493,  0x9479,  or  very  nearly 
the  same  that  it  was  at  first.  Thus  by  alternately  hammering  and  then 
heating  or  annealing  a  metal,  the  atoms  are  brought  more  closely  together 
or  pushed  further  apart.  When  the  atoms  are  pushed  further  apart,  the 
heat  becomes  potential  or  latent  ;  when  advanced  nearer  to  each  other,  the 
heat  is  actual  or  sensible.  Nearly  every  philosopher  selects  a  particular 
subject  to  which  he  devotes  his  special  attention.  Let  us  read  what  Dr. 
Tyndall  says  of  latent  heat  in  his  standard  work,  “  Heat  a  Mode  of  Motion.  ’ 

“We  shall  now  direct  our  attention  to  the  phenomena  which  accompany 
changes  of  the  state  of  aggregation.  When  sufficient!  /  heated,  a  solij  melts  ; 
and  when  sufficiently  heated,  a  liquid  assumes  the  form  of  gas.  Let  us  take 
the  case  of  ice,  and  trace  it  through  the  entire  cycle.  This  block  of  ice  h  .s 
now  a  temperature  of  to'’  C.  below  zero.  I  warm  it  ;  a  thermometer  fixed  in 
it  rises  to  o°,  and  at  this  point  the  ice  begins  to  melt ;  the  thermometric 
column,  which  rose  previously,  is  now  arrested  in  its  march ,  and  becomes 
perfectly  stationary.  I  continue  to  apply  warmth,  but  there  is  no  augmenta¬ 
tion  of  temperature  ;  and  not  until  the  last  film  of  ice  has  been  removed  horn 
the  bulb  of  the  thermometer,  does  the  mercury  resume  its  motion.  It  is  now 
again  ascending;  it  reaches  30°,  6o’,  ioo°  C.  ;  1  ere  steam-bubbles  appear  in 
the  liquid  ;  it  boils,  and,  from  this  point  upwards,  the  thermometer  remains 
stationary  at  100’.  But  during  the  melting  of  the  ice,  and  during  the  evapo¬ 
ration  of  the  water,  heat  is  incessantly  communicated.  To  simply  liquefy  the 
ice,  as  much  heat  is  imparted  as  would  raise  the  same  weight  of  water  79  4  L., 
or  as  would  ra  se  79’4  times  the  weight  one  degree  in  temperature  ;  and  to  con¬ 
vert  a  pound  of  water  at  ioo°  C.  into  a  pound  of  steam  at  the  same  tempeiatuie, 
537-2  times  as  much  heat  is  required  as  would  raise  a  pound  ot  water  one 
degree  in  temperature.  The  former  number,  79’4°  C.  (or  143  D),  represents 
what  has  been  hitherto  called  the  latent  heat  of  water  ;  and  the  latter  number, 
537'2°  C.  (or  967°  F.),  represents  the  latent  heat  ot  steam. 

“  It  was  manifest  to  those  who  first  used  these  terms,  that  throughout  t  k 
entire  time  of  melting,  and  throughout  the  entire  time  of  boiling,  heat  was 


HEAT. 


190 


communicated  ;  but  inasmuch  as  this  heat  was  not  revealed  by  the  ther¬ 
mometer,  the  fiction  was  invented  that  it  was  rendered  latent.  The  fluid  of 
heat  was  supposed  to  hide  itself  in  some  unknown  way  in  the  interstitial 
spaces  of  the  water  and  the  steam. 

“According  to  our  present  theory  (the  dynamical),  the  heat  expended  in 
melting  is  consumed  in  conferring  potential  energy  upon  the  atoms :  it  is 
virtually  the  lifting  of  a  weight.  So  likewise  as  regards  steam,  the  heat  is 
consumed  in  pulling  the  liquid  molecules  asunder — conferring  upon  them  a 
still  greater  amount  of  potential  energy. 

“  When  the  heat  is  withdrawn,  the  vapour  condenses,  the  molecules  again 
clash  with  a  dynamic  eneigy  equal  to  that  which  was  employed  to  separate 
them,  and  the  precise  quantity  of  heat  then  consumed  now  re-appears. 

“  The  act  of  liquefaction  consists  of  interior  work  expended  in  moving  the 
atoms  into  new  positions.  The  act  of  vaporization  is  also,  for  the  most  part, 
interior  work  j  to  which,  however,  must  be  added  the  exterior  work  of 

forcing  back  the  atmosphere,  when  the  liquid  becomes  vapour . 

Let  us  then  fix  our  attention  upon  this  wonderful  substance,  water,  and  trace 
it  through  the  various  stages  of  its  existence.  First,  we  have  its  constituents 
as  free  atoms  of  oxygen  and  hydrogen,  which  attract  each  other,  fall  or 
clash  together.  The  mechanical  value  of  this  atomic  act  is  easily  determined. 
The  heating  of  1  lb.  of  water  i°  C.  is  equivalent  to  1,390  foot-pounds  ;  hence 
the  heating  of  34,000  lbs.  of  water  i°  C.  is  equivalent  to  34,000X1,390  foot¬ 
pounds. 

“  We  thus  find  that  the  concussion  of  our  1  lb.  of  hydrogen  with  8  lbs.  of 
oxygen  is  equal,  in  mechanical  value,  to  the  raising  of  forty-seven  million 
pounds  one  foot  high. 

“  I  think  I  did  not  overstate  matters  when  I  stated  that  the  force  of  gravity, 
as  exerted  near  the  earth,  is  almost  a  vanisning  quality,  in  comparison  with 
these  molecular  forces. 

“  The  distances  which  separate  the  atoms  before  combination  are  so  small 
as  to  be  utterly  immeasurable ;  still  it  is  in  passing  over  these  spaces  that 
the  atoms  acquire  a  velocity  sufficient  to  cause  them  to  clash  with  the  tre¬ 
mendous  energy  indicated  by  the  above  numbers.  After  combination,  it  is  in 
a  state  of  a  vapour,  which  si  ks  to  ioo°  C.,  and  afterwards  condenses  into 
water.  In  the  first  instance  the  atoms  fall  together  to  form  the  compound; 
in  the  next  instance  the  molecules  of  the  compound  fall  together  to  form  a 
liquid.  The  mechanical  value  of  this  act  is  also  easily  calculated.  9  lbs.  of 
steam,  in  falling  to  water,  generate  an  amount  of  heat  sufficient  to  raise 
537'2  X  9 =4.835  lbs.  of  water  i°C.,  or  967  Xg  —  8,703  lbs.  i°  F.  Multiplying  the 
former  number  by  1,390,  or  the  latter  by  772,  we  have  in  round  numbers  a 
product  of  6,720,000  lbs.  as  the  mechanical  value  of  the  mere  act  of  con- 
densaticn. 

“  The  next  great  fall  is  from  the  state  of  liquid  to  that  of  ice,  and  the 
mechanical  value  of  this  act  is  equal  to  993,564  f  ot-pounds.  Thus  our  9  lbs. 
of  water,  at  its  origin  and  during  its  progress,  falls  down  three  great  pre¬ 
cipices  ;  the  first  fall  is  equivalent  in  energy  to  the  descent  of  a  ten  weight 
down  a  precipice  22,320  feet  high  ;  the  second  fall  is  equal  to  that  of  a  ton 
down  a  precipice  22,900  feet  high  ;  and  the  third  is  equal  to  the  fall  of  a  ton 
down  a  precipice  433  feet  high. 

“  I  have  seen  the  wild  stone-avalanches  of  the  Alps,  which  smoke  and 
thunder  down  the  declivities  with  a  vehemence  almost  sufficient  to  stun  the 


LATENT  HEAT 


191 


observer.  I  have  also  seen  snow-flakes  descending  so  softly  as  not  to  hurt  the 
fragile  spangles  of  which  they  were  composed  ;  yet  to  produce  from  aqueous 
vapour  a  quantity,  which  a  child  could  carry,  of  that  tender  material,  de¬ 
mands  an  exertion  of  energy  competent  to  gather  up  ihe  shattered  blocks  of 
the  largest  stone-avalanche  I  have  ever  seen,  and  pitch  them  to  twice  the 
height  from  which  they  fell.” 

Capacity  for  Heat. 

This  term,  which  is  most  simple  and  useful,  expresses  a  fact  that  has  been 
forced  upon  observers  by  numerous  experiments  made  with  the  thermometer. 
The  thermometer  is  usefully  applied  to  determine  the  temperature  of  any  solid, 
fluid,  or  gaseo  is  matter  ;  but  it  will  not  tell  the  observer  how  much  heat  or 
actual  energy  is  contained  in  different  measures  of  the  same  fluid.  A  gallon 
of  water  in  one  vessel,  and  a  pint  of  water  in  another,  may  be  shown  by  the 
thermometer  to  have  a  temperature  of  21 2°  F.  ;  but  the  quantity  of  energy  or 
heat  must  be  much  greater  in  the  larger  measure — the  one  gallon— than  in  the 
single  pint.  The  thermometer  fails  to  show  the  quantity  of  enetgy,  whilst  it 
gives  relatively  the  “  relative  actual  heat  ” — the  “  temperature.”  A  photo¬ 
meter,  or  measurer  of  light,  will  demonstrate  the  relative  illuminating  power  of 
any  given  source  of  light ;  but  it  cannot  give  the  number  of  vibrations  per 
second  producing  the  light.  A  thermometer  cai  tell  us  truthfully  how  m^ch 
hotter  or  colder  than  32"  or  21 2°  F.  a  substance  may  be  ;  but  it  cannot  inform 
us  what  may  be  the  amount  of  vibratory  power  given,  and  the  molecular  force 
detached,  which,  according  to  the  dynamical  theory,  must  be  the  equivalent 
for  the  expression  or  quantity  of  heat.  There  are  certain  facts,  explain  them 
how  we  will,  which  are  indisputable.  If  10  lbs.  of  water  (one  gallon)  at  ioo° 
F.  are  mixed  with  the  same  weight  of  oil  at  50°  F.,  the  resulting  temperature 
will  not  be  the  mean,  750  F.,  but  83-Jy0  F.  The  water,  therefore,  has  lost 
“actual  energy”  equal  to  i6§;  but  the  same  energy  has  caused  the  oil  to 
rise  33^. 

If  the  experiment  is  reversed,  and  10  lbs.  of  oil  at  ioo°  are  mixed  with  10  lbs. 
of  water  at  $oc,  the  mean  will  be  66^°:  the  335°  actual  heat  or  energy  given 
out  from  the  oil  is  only  able  to  raise  the  temperature  of  the  water  i6|°. 

The  actual  energy  which  will  raise  the  temperature  of  oil  2°  will  raise  an 
equal  quantity  of  water  only  i°.  The  heat  that  will  raise  any  given  substance 
from  o°  C.  to  i°  C.,  compared  with  the  amount  of  “  energy  ”  required  to  heat 
an  equal  weight  of  water  to  the  same  point,  is  called  its  “  specific  heat.’ 
Therefore  the  specific  or  potential  heat  of  oil  will  be  a  half,  '5,  ns  compared 
with  the  unit  or  one — viz.,  water. 

As  the  oil  has  been  quickly  heated,  so  it  will  rapidly  cool  ;  it  has  only 
half  the  “energy  of  heat”  possessed  by  water  to  give  up.  If  the  water 
require  one  hour  to  cool  tc  any  given  temperature,  the  oil  would  reach  the 
same  point  ip  half-an-hour. 

Hence  “time”  is  the  test  used  sometimes  to  determine  the  specific  heat  of 
bodies—  the  time  required  by  a  substance  to  cool.  Or  the  process  may  be 
leversed  by  a  curtaining  the  quantity  of  ice  which  exactly  equal  weights  of 
other  bodies  can  melt  in  falling  from  one  temperature  to  another,  say  from 
the  boiling-point  to  the  freezing-point  of  water.  As  the  process  of  mixture 
already  de.  cribed  with  the  oil  and  water  may  be  employed,  there  are  there¬ 
fore  three  methods  by  which  the  specific  heat  of  bodies  may  be  determined  : 


192 


HEAT 


1.  The  direct  method  by  mixture. 

2.  Time  required  to  cool,  and  rate  of  cooling. 

3.  Heating  of  ice,  and  quantity  liquefied  by  a  given  weight  of  the  substance' 
heated  to  2120  whilst  falling  to  320. 

By  the  first  method — viz.,  mixture  or  immersion — the  distinguished  phy¬ 
sicist,  Regnault,  arrived  at  the  following  results  : 


SPECIFIC  HEATS  OF  EQUAL  WEIGHTS  BETWEEN  O0  C.  AND  IOO°  C. 


Water 

1  -ooooo 

Brass 

0-09391 

Oil  of  turpentine 

0-42593 

Silver 

0-05701 

Charcoal. 

0-24150 

Tin 

0-05623 

Glass 

0-19768 

Mercury  . 

0-03332 

Iron 

0-11379 

Platinum 

0-03243 

Zinc 

0-09555 

Gold 

0-03244 

Copper  . 

0-09515 

Lead 

0-03140 

Aluminium 

0-21430 

Bismuth  . 

0-03080 

For  a  lecture-table  experiment  there  are  none  better  than  that  devised  by 
Tyndall,  to  show  the  time  required  by  equal  spheres  of  various  solids,  heated 
to  the  same  temperature,  to  melt  their  way  through  a  cake  of  beeswax. 

The  metals  used  are  iron,  lead,  bismuth,  tin,  copper:  these  are  shaped  as 
balls  or  spheres,  and  each  furnished  with  a  hook  for  conveniently  removing 
them  from  the  oil,  in  which  they  are  heated  to  a  temperature  of  i8o°C. 

A  framework  of  wood,  shaped  like  the  spokes  of  a  wheel,  with  five  strings, 
to  which  the  balls  are  attached,  may  be  used  in  order  to  remove  the  whole  of 
the  balls  at  once  from  the  heated  oil. 

When  they  are  laid  upon  a  cake  of  beeswax,  6  in.  in  diameter  and  half  an 
inch  thick,  supported  on  the  ring  of  a  tripod  or  other  convenient  means  of 
support,  the  iron  and  the  copper  balls  go  through  first,  the  tin  next,  while 
the  lead  and  bismuth  are  retained.  If  they  contained  the  same  amount  of 
heat,  or  had  the  same  “  actual  energy,”  they  would  all  go  through  the  wax  in 
the  same  time :  the  difference  in  their  specific  heats  determines  the  rate  at 
which  they  perforate  the  wax. 

Messrs.  Uulong  and  Petit  have  shown  that  the  specific  heat  of  bodies 
increases  as  their  temperature  rises.  Any  given  substance  will  require  more 
heat  to  raise  it  a  certain  number  of  degrees  when  at  a  high  than  at  a  low 
temperature.  The  variations  of  specific  heat  according  to  temperature  are  well 
shown  in  the  case  of  iron. 


SPECIFIC  HEAT  OF  IRON  (DULONG  AND  PETIT). 


From  320  to 

’9  99 

99  95 

59  59 


212° 

3920 

572 

666 


0U098 
o- 1 150 
oh  2 18 
0-1255 


In  a  similar  manner  the  specific  heat  of  the  gases  has  been  carefully  deter¬ 
mined,  the  methods  employed  involving  one  of  the  three  modes  already 
described.  De  la  Roche  and  Berard  caused  a  measured  volume  of  the  gas 
under  examination,  when  heated  to  a  fixed  temperature  and  kept  at  a  uniform 
heat,  to  pass  through  a  spiral  glass  tube  surrounded  with  water  (this  plan 
would  be  equivalent  to  the  “  mixture  ”  of  oil  and  water),  and,  by  observing  the 
increase  of  the  temperature  of  the  water  surrounding  the  spiral  tube,  and  other 
data,  they  determined  the  specific  heat  of  certain  gases. 


LATENT  HEAT. 


i93 


Dr.  Apjohn  devised  another  method,  viz.,  that  of  vaporizing  water  by  a 
current  of  the  heated  gases,  and,  by  inverse  proportion,  viz.,  the  greater  the 
specific  heat  of  the  gas,  the  less  time  required  to  cool  it,  and  vice  versa ,  he 
has  given  the  specific  heats  of  gases  already  examined  by  De  la  Roche;  but 
unfortunately  the  figures  of  the  two  experimentalists  did  not  agree,  and  there¬ 
fore  a  more  careful  investigation  was  made  by  Regnault,  who,  taking  the 
specific  heat  of  an  equal  weight  of  water  as  the  unit  of  comparison,  commences 
with  air,  and  gives  the  following  table  of  the  specific  heats  of  a  number  of 
gases  and  vapours  with  which  he  experimented  ;  and,  what  is  still  more  valu¬ 
able,  the  table  gives  the  specific  heat  of  equal  volumes  and  weights  of  the 
bodies  examined : 


SPECIFIC  HEAT  OF  GASES  AND  VAPOURS. 


GAS  OR  VAPOUR 

Equal 

Vols  |  Weight  j 

1 

; 

GAS  OR  VAPOUR. 

Equal 

Vols.  |  Weight. 

Air 

0-2375 

0-2375 

Sulphurous  an- 

Oxygen 

02405 

0-2175 

hydride  . 

0-341 

0-1540 

N  itrogen  . 

02  368 

0-2438 

Hydrochloric 

Hydrogen  . 

0-2359 

3-4090 

acid 

0-2352 

0-1842 

Chlorine 

0-2964 

o’  1 2 1 0 

Sulphuretted  hy- 

Bromine 

03040 

0-0555 

drogen  . 

0-2857 

0-2432 

Nitrous  oxide 

o-3447 

0-2262 

Water 

0-2989 

0-4805 

Nitric  oxide 

0-2406 

0-2317 

Alcohol 

0-7171 

o-4534 

Carbonic  oxide  . 

o"2t7  0 

02450 

Wood  spirit 

0-5063 

0-4580 

Carbonic  anliy- 

Ether . 

P2266 

0-4796 

dride 

0-3307 

02 1 63 

Ethyl  chloride  . 

0-6096 

0-2738 

Carbonic  distil- 

Ethyl  bromide  . 

0-7026 

o- 1 896 

phide 

0-4122 

0-1569 

Ethyl  disulphide 

I  -2466 

0-4008 

Ammonia  . 

0-2996 

0-5084 

Etr.yl  cyanide  . 

0-8293 

0*4261 

Marsh  gas  . 

0-3277 

0-5929 

Chloroform 

0-6461 

0*1566 

Olefiant  gas 

0-4106 

04040 

Dutch  liquid 

0-791  I 

0-2293 

Arsenious  chlo- 

Acetic  ether 

1-2184 

0-4008 

ride 

07013 

0-1122 

Benzol 

roi  14 

o-3754 

Silicic  chloride  . 

07778 

0-1322 

Acetone 

08341 

0-4125 

Titanic  chloride 

0-8564 

01 290 

Oil  of  turpentine 

2.3776 

0-5061 

Stannic  chloride 

0-8639 

0-0939 

Phosphorous 

chloride  . 

0-6386 

o-i347 

Regnault’s  experiments  confute  those  of  De  la  Roche  and  Berard,  and 
deny  that  the  specific  heat  of  air  and  all  gases  rises  with  the  temperature. 
Regnault’s  experiments  were  carried  on  with  air  between  the  limits  of  tem¬ 
perature  expressed  by  30°  C.  and  200°  C.  The  same  result  was  obtained  with 
gases  like  hydrogen,  which  cannot  be  easily  liquefied;  and  the  specific  heat 
was  not  found  to  increase  with  the  temperature,  at  least  between  30s  C.  and 
2000  C.  A  gas  which  can  be  easily  condensed,  such  as  carbonic  acid,  shows,  in 
accordance  with  the  statement  of  De  la  Roche  and  Berard,  an  increased 
specific  heat  with  an  increased  temperature. 


li 


J94 


HEAT. 


SPECIFIC  HEAT  OF  CARBONIC  ACID  AT  DIFFERENT  TEMPERATURES. 

Between  —  30°  and  8°  C.  .  .  specific  heat  0-18427 

„  —  8°  „  ioo°  .  .  .  „  „  0'20248 

„  —  8"  „  2IOc  .  .  .  „  „  0-21692 

Regnault  also  discovered  that  the  specific  heat  of  a  given  volume  of  a  gas 
increases  directly  as  its  density  is  increased ;  and  his  valuable  experiments 
show  that  the  specific  heat  of  the  same  liquid  varies  with  the  temperature. 

There  exists  a  remarkable  connection  between  specific  heat  and  atomic 
weight,  which  has  given  rise  to  another  term — “atomic  heat.”  This  expression 
means  the  product  obtained  by  multiplying  the  specific  heat  of  a  body  by  its 
atomic  weight. 

The  specific  heat  of  an  elementary  body  is  inversely  as  its  combining  pro¬ 
portion.  Regnault  discovered  in  upwards  of  twenty  bodies  chemically  pure, 
that  the  atomic  heat  ranged  between  3-31  and  2-93,  giving  a  mean  of  3-13. 
Hence,  if  the  above  number  3-13  is  divided  by  the  number  expressing  the 
specific  heat  of  iron,  lead,  mercury,  tin,  &c.,  the  quotient  gives  very  nearly 
the  atomic  weight  of  the  metal. 

The  term  “  atomic  weight”  must  not  be  confounded  with  the  term  “  chemical 
equivalent:”  the  latter  is  obtained  by  direct  experiment,  and  means  the  com¬ 
bining  proportion  of  the  various  elements,  as,  for  instance,  1  being  taken  as 
the  combining  proportion  or  equivalent  for  hydrogen,  16  will  be  that  of 
oxygen  ;  or  1  of  hydrogen  may  displace  65  of  zinc :  hence  the  former  is  equiva¬ 
lent  to  the  latter. 

Atomic  weight  is  a  product  arrived  at  by  calculations  carried  out  in  various 
ways,  as,  for  instance,  when  the  number  3-13  is  divided  by  the  specific  heat  of 
a  metal. 

Atomic  weight  is  a  product  arrived  at  by  calculations  carried  out  in  various 
ways,  as,  for  instance,  when  the  number  3-13  is  divided  by  the  specific  heat 
of  a  metal.  Atomic  weight  is  also  arrived  at  by  other  methods  ;  it  may  some¬ 
times  coincide  with  tfie  combining  proportion,  or  equivalent  number,  or  it 
may  be  a  multiple  of  it.  One  of  Dr.  Black’s  bases  of  the  theory  of  latent  heat 
is  that,  “  the  pressure  remaining  the  same,  there  is  a  definite  melting-point 
for  every  solid  ;  and  (provided  the  mass  be  stirred)  however  much  heat  be 
slowly  applied,  the  temperature  of  the  whole  remains  at  the  melting-point 
tiil  the  last  particle  is  melted.” 

“Actual  energy  ”  (heat)  disappears  during  liquefaction.  When  matter  passes 
from  the  solid  to  the  liquid  state,  “  actual  ”  is  converted  into  “  potential 
energy  ;”  and  the  heat  is  said  to  disappear,  and  cold  is  produced.  It  is  the 
enormous  amount  of  actual  heat,  so  slowly  converted  into  potential  heat, 
that  prevents  the  sudden  liquefaction  of  ice  or  snow,  and  the  great  damage 
which  would  occur  to  property  if  the  snow  could  be  quickly  melted.  Con¬ 
versely,  when  a  liquid  is  changed  to  the  solid  state,  the  closer  proximity  of  the 
molecules,  the  merging  together  of  the  particles  by  cohesion,  converts  the 
“  potential  ”  into  “  actual  ”  heat  ;  and  thus  the  very  change  of  water  into 
snow  or  ice  produces  actual  energy,  or  heat,  and  helps  to  mitigate  the  effect 
of  a  sudden  frost 

Taking  the  fact  (irrespective  of  theory)  that  liquefaction  will  produce  cold, 
there  are  various  solids  and  mixtures  of  solids  which  will  produce  a  sufficiently 
low  temperature,  when  quickly  dissolved  in  water,  to  freeze  water  contained 
in  a  vessel  surrounded  with  the  mixture.  The  mere  solution  of  nitre  alone 
wilj  lower  the  temperature  tf  water  from  50°  to  350  F.  Four  ounces  of  nitre 
and  four  ounces  of  common  sal  ammoniac  dissolved  in  four  ounces  of  water 
reduce  the  temperature  from  50  '  F.  to  io°  F.  A  mixture  of  equal  parts  of 


LATENT  HEAT 


T95 


snow,  or  powdered  ice,  and  salt  will  sink  the  thermometer  from  320  F.  to  0°, 
or  32  degrees  below  the  freezing-point  of  water;  and  two  of  snow  r.nd  one  of 
salt  reduce  the  temperature  to  —  40  F.  A  mixture  of  three  parts  by  weight  of 
chloride  of  calcium  and  two  of  snow  will  reduce  the  temperature  from  320  F. 
to  —  50°F. ;  and  by  powdering  and  carefully  cooling  the  chloride  to32°F.,and 
using  very  thin  vessels,  mercury  can  be  frozen.  The  liquefaction  of  a  metallic 
alloy,  composed  of  207  parts  by  weight  of  lead,  1 18  of  tin,  and  284  of  bismuth, 
in  1,617  parts  of  mercury,  will  sink  the  thermometer  from  63°  to  140;  and,  of 
course,  water  can  be  frozen  by  this  process. 

One  of  the  most  interesting  experiments  is  that  of  Mousson,  who  contrived 
an  apparatus  by  which  ice  was  subject  to  a  pressure  equal  to  thirteen  thousand 
atmospheres,  and  by  which  its  bulk  was  reduced  by  thirteen-hundredths  of 
that  which  it  occupied  at  o°  C.  (32°  F.). 

The  temperature  of  the  ice  was  first  reduced  —  20°  C.  (  —  4°  F.),  and  then 
subjected  to  the  pressure  of  a  copper  rod,  worked  by  a  very  powerful  screw. 


Fig.  165. — A  Still ,  with  “  Still  Head?  and  the  Worm  surrounded  by  Cold 

Water. 

Instead  of  increasing  the  solidity  of  the  ice,  the  mechanical  compression  and 
motion  of  the  molecules  liberated  the  equivalent  in  actual  energy  or  heat ;  the 
ice  liquefied,  and  the  copper  rod  was  found  to  have  fallen  to  the  bottom  of 
the  water,  which  again  solidified  directly  the  pressure  was  removed. 

The  freezing-point  of  water  is  lowered  to  a  minute  extent  by  pressure. 

\  liquid  alloy  of  sodium  and  potassium  is  easily  obtained  by  pressing 
pieces  of  the  two  metals  together :  if  this  liquid  be  brought  into  contact  with 
mercury,  the  amalgam  instantly  solidifies  and  becomes  hard  ;  at  the  same 
time  so  much  heat  is  liberated  that  incandescence  is  apparent  at  the  point 
where  the  metals  come  in  contact,  and  any  combustible  fluid,  such  as  naphtha, 
may  be  set  on  fire.  Liquefaction  produces  cold  ;  congelation  or  solidification, 
heat. 

If  liquefaction  is  pressed  further  by  the  addition  of  more  heat,  the  water 
is  converted  into  vapour,  the  molecules  are  thrust  wider  apart,  and  actual 
heat  v  disappears. 

13 — ? 


196 


HEAT. 


This  is  demonstrated  very  conclusively  in  the  distillation  of  water.  The 
heat  is  applied  to  the  bottom  of  the  vessel  containing  the  water,  and  when  it 
has  once  reached  the  boiling-point,  2120,  the  steam — the  vapour  (also  at  2120) 
cairies  off  all  the  heat  of  the  burning  coals  ;  the  heat  disappears  ;  the  ther¬ 
mometer,  inserted  in  the  still,  remains  stationery.  When  the  steam  is  passed 
through  the  condensing  apparatus — the  coil  of  pipe,  called  the  worm,  sur¬ 
rounded  by  cold  water,  and  contained  in  what  is  called  the  worm-tub— the 
heat  or  energy  which  it  carries  off  from  the  fire  becomes  apparent  ;  the  stored 
heat  is  so  large  in  quantity  that  it  soon  raises  the  temperature  of  the  water  in 
the  worm-tub,  and  the  quantity  of  water  in  the  tub,  which  may  be  raised  to 
2120  F.,  is  much  larger  than  the  water  condensed.  The  stored  “heat” 
(already  so  often  spoken  of  as  “  potential  heat  ”)  in  the  steam  becomes 
“actual”  energy  when  the  vapour  passes  to  the  liquid  condition  of  matter; 
and  this  heat,  as  already  described,  is  so  great,  that  it  may  be  conveniently 
applied  in  the  warming  of  buildings. 

The  conversion  of  water  into  vapour  by  the  method  already  described  is 
progressive,  and  unattended  with  danger.  If  the  water  could  be  suddenly 
converted  into  steam,  and  the  specific  heat  of  steam  was  not  so  high,  the 
attempt  to  boil  water  must  always  end  disastrously,  because  it  would  be 
generated  suddenly  and  explosively  ;  the  steady  “  ebullition,”  or  escape  of 
bubbles  of  steam,  as  the  cohesion  ot  the  molecules  is  gradually  overcome, 
would  not  be  maintained.  The  escape  of  air  from  water,  heated  to  2123  F.,  is 
very  apparent  when  it  is  boiled  in  a  flask.  Tyndall  says  the  air  acts  as  a 
kind  of  elastic  spring,  pushing  the  atoms  of  the  water  apart,  and  thus  helping 
them  to  take  a  gaseous  form. 

The  cohesion  of  the  particles  of  water  appears  to  be  greatly  increased  when 
the  foreign  matter — viz.,  atmospheric  air — is  removed.  Thus,  water  allowed 
to  fall  through  a  tube  from  which  the  air  has  been  ejected  by  boiling  the 
water,  and  melting  the  glass  and  hermetically  sealing  the  end,  falls  col¬ 
lectively,  making  a  noise,  and  would  break  through  the  end  of  the  glass  tube 
like  a  solid  substance.  The  vacuum-tube  containing  the  water  is  called  “  the 
water-hammer,”  and  if  altered  in  shape  by  bending  it  into  a  V-shaped 
figure,  nicely  rounded  off  at  the  bend,  some  very  amusing  illustrations  of  the 
modification  of  the  cohesion  of  the  water  and  adhesion  to  the  glass  can  be 
displayed. 

The  mechanical  nature  of  the  interior  of  a  vessel  in  which  steady  “ebulli¬ 
tion”  is  to  be  maintained  greatly  affects  the  escape  of  the  vapour  or  steam. 
If  the  interior  surface  is  too  smooth,  like  that  of  a  flask,  and  distilled  water 
boiled  therein,  the  flask  is  said  to  bump,  i.e.,  the  temperature  of  the  boiling 
water  rises  a  degree  or  so  above  the  boiling-point,  and  every  time  steam  is 
formed  it  escapes  with  a  sudden  jerk,  as  if  it  were  a  slight  explosion,  and  the 
temperature  falls  to  21 2°,  again  rising  and  falling  with  each  rush  of  vapour. 
When  this  occurs,  it  may  be  instantly  corrected  by  dropping  in  any  metallic 
filings,  zinc  or  copper,  or  by  placing  in  the  flask  a  bit  of  crumpled  platinum- 
foil.  The  rough  edges  break  up  the  continuity  of  the  smooth  surface  of  the 
glass,  and  serve  to  conduct  the  heat  of  the  lamp  into  the  particles  of  the  water, 
and  thus  to  hasten  the  disruption  of  their  cohesive  power.  It  is  easy  to  follow 
out  the  idea  further  by  lining  a  copper  vessel  with  shellac.  Water  placed  in 
a  vessel  prepared  in  this  manner  will  not  boil  until  it  attains  a  temperature 
of  2193  F.,  i.e.,  seven  degrees  above  the  ordinary  boiling-point.  Bursts  of 
steam  occur,  the  temperature  falling  after  each  escape  of  vapour  to  212'.  The 


LATENT  HEAT 


•97 


hard  copper  is  not  in  direct  communication  with  the  water  ;  there  is  an 
intermediate  non-metallic  body  which  adheres  to  it  and  becomes  soft.  It  is 
this  intermediate  physical  condition,  neither  solid  nor  fluid,  but  partaking  oi 
the  physical  nature  of  both,  which  interferes  with  the  energy  of  heat,  and 
assists  to  maintain  the  cohesion  of  the  water. 

Monsieur  Donny,  of  Ghent,  has  studied  this  subject  very  carefully,  and  lias 
shown  that  the  presence  of  air  is  of  great  importance  in  maintaining  steady 
ebullition  and  escape  of  vapour  from  water  ;  the  tiny  volumes  of  air  expand  by 
heat,  and  into  these  bubbles  the  steam  passes,  expands,  and  rises. 

All  spring  and  river  water  contains  air  in  solution,  and,  as  steam-boilers 
are  constantly  fed  with  fresh  water,  the  supply  of  bubbles  of  air  goes  on  con¬ 
tinually. 

That  the  presence  of  air  in  solution  does  assist  the  escape  of  the  steam  is 
proved  by  the  explosive  nature  conferred  on  water  after  it  has  been  boiled  for 
a  lengthened  period,  so  as  to  get  rid  of  and  drive  off  the  dissolved  air. 

Under  these  circumstances  the  temperature  of  the  water  rises  to  360°  F.,  or 
148°  above  the  boiling-point  ;  and  such  was  the  violence  with  which  the 
steam  escaped,  that  an  open  glass  vessel  was  shattered  with  a  loud  report. 


Fig.  166. — Faraday’s  Experiment — Boiling  Water  deprived  of  Air 

under  Oil  of  Turpentine . 

a,  the  tube  containing  the  oil  amt  ice;  b,  the  spirit-lamp;  c,  the  screen  of  blotting-paper  to  receive 
the  water  anil  oil  when  ejected  explosively. 

In  great  manufactories,  boilers  “banked  up,”  and  kept  gently  boiling  from 
Saturday  night  to  Monday  morning  by  a  slow  expenditure  of  fuel,  have 
exploded  without  warning,  and  without  the  engineer  having  the  slightest 
conception  of  any  dangerous  accumulation  or  pressure  of  steam.  Amongst 
the  precautions  taken  to  prevent  accidents  is  one  suggested  by  the  recollection 
of  this  property  of  water;  and  means  should  be  taken  to  allow  a  small 
quantity  of  fresh  cold  water  to  pass  continually  into  all  boilers  during  the 
intervals  of  rest,  and  especially  into  locomotives  which  are  sometimes  kept 
“  banked  up”  and  ready  for  service. 

When  water  freezes,  the  air,  by  the  compression  of  the  particles,  is  squeezed 
out,  and  none  remains  in  solution.  If  a  piece  of  Wenliam  or  clear  Norwegian 


ice  is  placed  in  a  tube  and  surrounded  with  oil  of  turpentine,  and  then  care¬ 
fully  melted  and  heated,  the  boiling-point  is  raised  very  high,  and,  directly 
steam  is  generated,  the  whole  contents  of  the  tube  are  ejected.  This  experi¬ 
ment  was  first  shown  by  Faraday  at  the  Royal  Institution.  (Fig.  1-66.) 

On  the  principle  that  the  more  we  increase  cohesive  force,  the  greater  must 
be  the  power  of  resisting  the  energy  of  heat,  is  explained  the  rise  in  the 
boiling-point  of  saline  solutions.  A  saturated  solution  of  nitrate  of  soda  boils 
at  a  temperature  of  249'5°  F. ;  the  quantity  of  salt  being  224^8  parts  in  100 
of  water,  or  more  than  double  the  weight  of  the  solvent.  Faraday  and 
Magnus  have  both  shown  that  the  steam  arising  from  the  boiling  saline  solution, 

although  escaping  at  a  temperature  of  249’5°  F.,  speedily 
W  and  almost  instantaneously  adjusts  itself  to  the  atmo- 

|]  spheric  pressure  indicating  only  the  ordinary  tempera¬ 

ture  of  steam — 21 2°  F.  When  it  is  said  that  water  boils 
at  2120  at  the  ordinary  pressure,  it  is  meant  that  the 
energy  of  heat,  represented  'by  the  steam,  cannot  exert 
itself,  cannot  even  help  the  vapour  to  escape,  unH  it 
has  overcome  the  pressure  of  the  air,  or  weight  equal 
to  fifteen  pounds  upon  the  square  inch.  The  lifting 
power  or  energy  of  heat  is  well  illustrated  by  this  sim¬ 
ple  fact ;  and  directly  the  pressure  is  partly  removed, 
the  amount  of  energy,  or  heat,  represented  by  the  boil¬ 
ing-point  is  reduced,  and  the  water  will  enter  into 
ebullition  at  a  lower  temperature.  The  pressure  of  the 
air  is  represented  by  the  height  at  which  a  column  of 
mercury  is  supported:  when  the  mercury  is  i6'6  inches 
high,  water  boils  at  i84c  F. ;  if  the  pressure  is  doubled, 
and  the  barometer,  the  column  of  mercury,  stands  at 
32'3  inches,  water  boils  at  216°  F.  The  difference  be¬ 
tween  i6‘6  inches  and  32-3  inches  is  very  great,  and  it 
might  be  thought  that  such  a  fall  in  the  barometer  could 
only  be  demonstrated  by  artificial  means,  and  by  the 
creation  of  a  partial  vacuum  with  an  air-pump.  But  it 
must  be  remembered  that  there  are  certain  spots  on 
the  surface  of  the  globe  where  the  adventurous  traveller 
may  ascend  nearly  three  miles  above  the  level  of  the 
sea. 

The  famous  De  Saussure  ascended  to  the  summit  of 
Mont  Blanc,  which  is  15,650  feet  above  the  level  of  the 
sea,  and  where  water  boils  at  a  temperature  of  185  '8°  F., 


Figs.  167  and  168. — Apparatus  for  determining  Elevations  by  the  Tempera¬ 
ture  of  the  Boiling-point  of  Water. 


STEAM. 


199 


and  the  barometer  stands  at  about  17  inches.  The  boiling-point  of  water  is 
lowered  about  one  degree  for  every  590  feet.  Dr.  Saussure’s  observations 
were  verified  by  Tyndall  in  August,  1859,  when  the  temperature  of  boiling 
water  at  the  summit  of  Mont  Blanc  was  found  to  be  184 '95°  F. 

It  is  by  the  careful  observation  of  the  temperature  at  which  water  boils 
that  the  height  of  any  hill  or  mountain  may  be  determined.  Since  Dr  Wol¬ 
laston  constructed  his  instrument  for  measuring  heights  by  the  observation  of 
the  boiling-point,  improvements  have  been  made,  as  shown  in  Fig.  167. 

The  Barometrical  Thermometer,  or  Hypsometrical  Apparatus,  as  con¬ 
structed  by  Negretti  and  Zambra,  is  intended  to  meet  the  requirements  of 
travellers  in  circumstances  where  the  mercurial  barometer  cannot  be  conve¬ 
niently  employed.  The  instrument  is  very  portable,  and  affords  a  ready  and 
accurate  means  of  measuring  heights  by  observation  of  the  temperature  of 
boiling  water.  The  apparatus  is  shown  in  Fig.  167.  It  consists, 

First,  of  a  very  delicate  thermometer,  about  12  in.  long,  the  scale  ranging 
from  180°  to  212°,  having  each  degree  subdivided,  so  as  to  show  distinctly  o°'i. 

Secondly,  a  copper  boiler,  C,  attached  to  a  small  tripod  stand.  From  the 
boiler  proceeds  three  double  tubes,  E  E  E  and  D  D  D,  open  at  top ;  screwed 
on  the  top  of  the  boiler;  the  outer  tube  has  two  openings,  one  at  the  top, 
through  which  the  thermometer  E  E  is  inserted,  passing  down  to  within  an 
inch  of  the  water  in  the  boiler,  and  supported  by  means  of  an  india-rubber 
washer,  as  shown  in  Fig.  167,  the  second  opening  forming  an  outlet  for  the 
steam,  as  shown  at  G.  The  object  of  th;  double  tube  is  to  insure  a  steady 
boiling-point,  which  it  would  be  impossible  to  obtain  in  open-air  experiments, 
were  only  a  single  tube  employed.  A  is  a  metallic  spirit-lamp,  surrounded 
with  wire  gauze,  B,  to  prevent  the  flame  being  extinguished  when  experi¬ 
menting  in  the  open  air.  The  whole  instrument,  when  packed  for  travelling, 
is  shown,  drawn  to  a  smaller  scale,  in  Fig.  168.  Each  instrument  is  furnished 
with  a  carefully  computed  set  of  tables,  from  which  may  be  obtained,  by  an 
easy  calculation,  the  elevation  corresponding  to  any  observed  boiling-point 
between  the  temperatures  of  180°  and  212° 

To  use  the  boiling-point  apparatus,  it  is  simply  necessary'  to  pour  into  the 
boiler,  through  the  small  opening  F,  on  its  surface,  a  sufficient  quantity  of 
water  to  fill  it  about  one-third,  and  afterwards  close  it  by  means  of  the  screw 
for  that  purpose;  the  lighted  spirit-lamp  is  then  applied,  and  when  the  water 
is  made  to  boil,  the  steam  rises,  surrounding  the  bulb  and  tube,  and,  descend¬ 
ing  between  the  two  tubes,  issues  from  the  opening  at  G.  After  a  tew  seconds, 
the  mercury  in  the  thermometer  will  rise  and  become  stationary;  the  degree 
indicated  by  it  must  then  be  noted,  when,  by  reference  to  the  tables,  the 
elevation  of  the  spot  where  the  experiment  has  been  performed  may  be  obtained. 

- ♦ - 

STEAM. 

If  water  boils  at  a  lower  temperature  when  the  ordinary  pressure  ol  the  air 
is  reduced,  it  should,  of  course,  indicate  a  higher  temperature  when  the  pres¬ 
sure  is  increased. 

Steam,  escaping  from  an  open  vessel,  is  usually  at  a  temperature  of  212  ; 
but  it  must  always  be  remembered  that  the  barometer  shows  that  the  pressure 
of  the  air  is  constantly  varying,  and,  even  within  the  limits  of  the  range  ot  the 


200 


HEAT. 


barometrical  indications  in  our  climate,  the  boiling-point  of  water  may  vary 
nearly  five  degrees.  “  The  pressure  remaining  the  same,  there 
is  a  definite  boiling-point  for  the  free  surface  of  every  liquid  ; 
and  (provided  the  mass  be  stirred)  however  much  heat  be 
applied,  the  temperature  of  the  whole  remains  at  the  boiling- 
point  until  the  last  particle  is  evaporated.” — Tait. 

The  temperature  of  steam  is  always  the  same  as  that  of  the 
water  from  which  it  is  evolved.  Consequently,  if  water  is  con¬ 
fined  in  a  closed  and  strong  vessel,  the  temperature  of  the  water 
may  be  raised  as  high  as  the  strength  of  the  vessel  will  permit. 

Marcet's  boiler  is  a  very  useful  and  safe  piece  of  apparatus 
for  demonstrating  the  rise  of  the  temperature  of  the  steam  as 
the  pressure  is  increased.  When  the  water  has  been  poured 
into  the  boiler,  and  the  heat  of  the  spirit-lamp  applied,  it  soon 
boils;  and,  if  the  stop-cock  remains  open,  the  temperature  is 
shown  to  be  21 2°  F.,  and,  of  course,  no  mercury  rises  in  the 
barometer  tube.  If,  however,  the  stop-cock  is  closed,  the  rise 
of  the  mercury  in  the  barometer  is  simultaneously  accom¬ 
panied  with  an  elevation  of  temperature  indicated  by  the  ther¬ 
mometer  ;  and  when  the  mercury  rises  to  30  in.,  it  demon¬ 
strates  that  the  pressure  is  doubled,  and  amounts  to  thirty 
pounds  upon  the  square  inch,  because  there  is  not  only 
the  pressure  of  the  air,  but  the  weight  of  the  mercury  to 
be  overcome,  before  the  latter  can  be  pushed  up  the  open 
tube  ;  and  looking  at  the  thermometer,  it  will  now  be 
found  to  stand  at  2505°  F. 

The  question  of  the  exact  pressure  which  accom¬ 
panies  a  rise  of  temperature  in  the  boiling-point  of 
water,  and  simultaneously  of  the  steam  escaping  from 
it,  was  very  properly  made  the  subject  of  careful 
scientific  inquiry  by  the  Academy  of  Sciences  at 
Paiis,  many  years  ago,  by  MM.  Dulong  and  Arago. 

They  obtained  facts  by  experiment  up  to  25  atmo¬ 
spheres,  and  from  the  data  so  obtained  calculated  the 
temperature  and  pressure  up  to  fifty  atmospheres,  or 
50  X  15  =750  pounds  upon  the  square  inch ;  giving,  by 
calculation,  a  temperature  of  510-4°  F. 

a,  a  strong  brass  globe,  made  of  two  hemispheres  screwed  together  with  flanges,  and  supported  on 
a  tripod  stand  ;  b,  the  barometer  tube  passing  through  a  steam-tight  collar,  and  touching  the  bottom 
of  the  boiler,  in  which  sufficient  mercury  to  fill  the  tube  and  cover  the  end  of  the  barometer  tube  is 
placed ;  c,  the  thermometer  graduated  to  400°  F.,  and  passing,  like  the  barometer  tube,  through  a 
oleam-tight  collar,  d  is  the  stop-cock ;  e,  a  spirit-lamp. 


FORCE  AND  TEMPERATURE  OF  STEAM. 


Atmosphere 

Temperature 

Atmosphere. 

Temperature. 

I 

212  ‘00°  F. 

9 

350-78°  F. 

2 

25CF52 

10 

358-88 

3 

275M8 

1 1 

366-85 

4 

29372 

12 

374-00 

5 

307-50 

13 

380-66 

6 

320-36 

14 

386-94 

7 

33170 

15 

392-86 

8 

34178 

16 

398-48 

STEAM. 


20  T 


Atmosphere. 

Temperature. 

Atmosphere. 

Temperature. 

1 7 

403 ’82°  F. 

22 

427*28°  I 

18 

408 '9  2 

23 

431‘42 

19 

41378 

24 

435*56 

20 

418-46 

25 

439*34 

21 

422*96 

The  above  temperatures  and  pressures  apply  only  to  steam  in  contact  with 
water.  “  Dry  steam”  is  affected  by  heat  precisely  in  the  same  manner  as  the 
permanent  gases. 

The  energy  called  heat  is,  as  we  have  seen  in  the  remarkable  experiment  of 
Groves,  capable  of  application  until  a  body  is  decomposed  into  its  elements 
(seep.  1 5  2, “  The  Decomposition  of  Steam  by  Heat  into  Oxygen  and  Hydrogen”). 
It  is  not  then  surprising  that  the  instrument  called  Papin’s  digester  should 
exert  such  a  powerful  solvent  action  upon  matter  subjected  to  the  high  tempera¬ 
ture  of  steam  produced  by  confining  and  heating  water  in  a  very  strong  vessel. 

In  using  an  ordinary  still  for  obtaining  distilled  water,  supposing  one 
gallon  of  distilled  water  to  be  obtained,  and  the  steam  representing  that  mea¬ 
sure  of  water  to  have  been  passed  into  five  gallons  and  a  half  of  ice-water— 
viz.,  water  at  a  temperature  of  320  F.,--the  energy  or  heat  carried  up  from  the 
fire,  and  converted  for  a  brief  space,  in  passing  from  the  still  to  the  worm, 
into  potential  or  stored  force,  is  so  great  that  it  will  raise  the  5-5  gallons  of 
water  at  320  to  21 2°  F.  when  condensed  or  converted  into  actual  energy  or 
heat.  The  elasticity  of  the  molecules  of  water  must  be  enormous,  to  permit 
the  vibratory  power  or  energy  called  heat  to  separate  them  so  widely  apart. 
By  the  same  amount  that  they  are  separated,  so  they  must  return.  The  act  of 
unlocking,  or  conversion  into  steam,  is  followed  by  condensation — the  locking 
of  the  molecules,  and  the  production  from  that  motion  of  an  enormous  amount 
of  heat,  usually  spoken  of  as  “latent  heat”— a  term  that  may  be  usefully  re¬ 
tained  so  iong  as  the  cause,  “  motion,”  is  not  lost  sight  of.  The  “  latent  heat  ” 
of  vapour  is  a  question  of  considerable  importance.  The  illustrious  Watt 
observed  by  experiment  that  the  same  weight  of  steam,  whether  it  escapes  at 
2120  or  300°  F.,  exhibits  very  nearly  the  same  amount  of  heating  power  or 
latent  heat  ;  and  although  Regnault,  by  more  elaborate  experiments,  has 
determined  “that  the  total  quantity  of  heat  necessary  for  the  evaporation  of 
water  increases  with  the  temperature,”  it  is  found  in  practice  that  Watt’s  con¬ 
clusion,  that  the  latent  heat  of  steam  is  increased  in  the  proportion  that  the 
“  sensible  heat  ”  is  absorbed,  is  suffic’ently  correct  for  ordinary  working 
purposes. 

A  given  weight  of  steam  at  2 1 20,  condensed  at 

32°  F.,  evolves . rSo°  sensible  heat, 

950°  latent  heat. 


1130 


The  same  weight  of  steam  at  250°  .  .  .218°  sensible  heat, 

912’  latent  heat. 


1130 


202 


HEAT. 


The  same  weight  of  steam  at  ioo°  .  .  .  68°  sensible  heat, 

1062°  latent  heat. 


1130 


Regnault’s  experiments  show  that  the  total  quantity  of  heat  necessary  to 
evaporate  water  at  ioo°  C.  (212  F.)  is  equal  to  637  ;  at  120°  C.,  it  is  643  ;  at 
150°  C.,  it  is  651.  These  conclusions  are  at  variance  with  those  arrived  at  by 
Watt,  but,  as  already  stated,  are  too  minute  to  affect  the  main  question. 

To  work  out  the  figures  representing  the  latent  heat  of  steam,  a  simple 
■arrangement  of  apparatus  may  suffice. 


Fig.  170. — Flasks  arranged  to  show  the  Latent  Heat  of  Steam. 

Thus,  supposing  each  flask  to  contain  eight  ounces  of  water  at  6o°  F.,  and 
the  steam  from  one  of  them  be  conducted  into  the  other  until  the  temperature 
is  raised  to  1880  F.,  or  increased  128°,  it  will  be  found  that  one  flask  has  lost 
one  ounce  of  water,  which  the  other  has  gained. 

The  whole  heat  carried  over  with  the  one  ounce  of  steam  into  the  eight 
ounces  of  water  will,  therefore,  be  I28;'x8  =  1024°. 

But  the  i024°cannot  be  all  regarded  as  latent  heat,  because  the  steam,  whilst 
condensing,  should  have  raised  the  water  to  2120  F. ;  therefore,  1880  F.  must 
be  deducted  from  2120  F.,  which  will  leave  240;  and  now  1024° — 24°=iooo°, 
the  latent  heat  of  steam. 

When  the  steam  is  allowed  to  escape  from  the  Marcet  boiler  (p.  173)  at  ; 
pressure  of  two  atmospheres,  and  at  a  temperature  of  25o-5°  F.,  it  would  be 
imagined  that  the  steam  must  severely  scald  the  hand  if  held  in  the  jet  whilst 
escaping  under  these  circumstances.  Curious  to  say,  this  is  not  the  case:  the 
steam,  as  it  escapes,  is  comparatively  cool,  and  the  hand  may  be  held  in  it  with 
perfect  impunity. 


STEAM. 


203 


Here  expansion  takes  place ;  the  particles  of  the  vapour  of  the  water  are 
closely  packed  and  squeezed  together;  the  steam,  whilst  inside  the  boiler,  is  of 
greater  density ;  the  heat  apparent  is  “actual  force,”  but  directly  it  escapes 
work  is  consumed  in  the  return  of  the  vapour  to  its  normal  state  of  pressure, 
and  thus  the  heat  becomes  “  potential,”  or  is  rendered  latent  or  insensible. 

Any  gas  or  vapour  in  the  act  of  expanding,  that  performs  work,  consumes 
heat. 

If  air  is  compressed  in  a  strong  cylinder  and  allowed  to  escape,  the  elastic 
force  which  pushes  out  the  air  represents  work;  and  as  heat  is  consumed,  the 
stream  of  air  is  found  to  be  cold.  When  air  is  forced  out  of  the  nozzle  of  a 
common  pair  of  bellows,  the  air  is  slightly  warmer  than  the  external  air,  be¬ 
cause  it  is  the  human  muscles  that  do  the  work :  it  is  the  stoppage  of  the 
motion  of  the  air  from  the  bellows  that  produces  the  slight  increase  of  heat. 
It  was  not  the  elastic  force  of  the  air  behind  the  escaping  portion  (as  with  the 
compressed  air  in  the  iron  vessel)  that  caused  the  air  to  escape  from  the  bellows; 
it  was  human  strength,  and  if  that  had  not  been  sufficient  no  air  would  have 
escaped  :  a  baby  cannot  work  a  pair  of  bellows.  It  was  formerly  taken  for 
granted  that  in  every  case  where  gases  and  vapours  expand  cold  must  be  pro¬ 
duced  ;  but  Gay-Lussac  and  J.  P.  Joule  have  clearly  proved  that  you  may  have 
expansion  without  producing  cold,  provided  no  work  is  performed. 


Fig.  1 7 i. — Gay-Lussac’s  Experiment. 

A,  b,  two  copper  cylinders;  c,  the  connecting-pipe  and  stop-cock. 


This  experiment  proves  very  beautifully  that  where  no  work  is  performed 
there  is  no  cold ;  and  in  this  experiment  gas  is  allowed  to  expand  without  doing 

work. 

The  vessel  A  is  first  exhausted,  and  the  other,  R,  left  full  of  air ;  when  the  cock 
is  turned,  the  air  rushes  out  of  B  into  A.  The  air  which  formerly  filled  B  is 
now  divided  between  B  and  A,  and,  if  pumped  back,  would  again  fill  R.  The 
half,  in  expanding  from  B  into  A,  has  performed  work,  and  consumed  heat.  It 
is  cold ;  but,  striking  against  the  interior  of  the  copper  vessel  A,  its  motion  i< 
stopped,  and  heat  is  generated.  The  heat  produced  in  A  by  the  arrest  of  motion 
is  exactly  equivalent  to  the  loss  sustained  in  B  by  work,  by  the  exertion  of  the 
elastic  force;  hence  the  two  effects  of  cold  and  heat  neutralize  each  other,  and 


204 


STEAM. 


the  temperature  of  the  air  in  the  two  vessels,  when  thoroughly  mixed,  remains 
unaltered.  There  is  no  work  performed,  and  no  heat  lost. 

A  still  more  satisfactory  experiment  was  performed  by  J.  P.  Joule.  He  com¬ 
pressed  air  with  a  force  equal  to  twenty-two  atmospheres  into  a  metallic  vessel 
— he  had  twenty-two  atmospheres  squeezed  into  a  space  usually  containing  one 
only  ;  he  pumped  the  air  out  of  a  similar  metallic  vessel,  producing  a  vacuum. 
The  vessels  were  connected,  like  Gay-Lussac’s,  with  a  tube  and  stop-cock,  and 
surrounded  with  water.  On  turning  the  cock,  the  air  expanded  from  one  vessel 
into  the  other,  and,  by  keeping  the  water  surrounding  both  vessels  properly 
stirred,  no  increase  or  decrease  of  heat  was  observed  in  the  water.  The  —  heat 
or  cold  in  one  vessel  exactly  balanced  the  -|-  heat  in  the  other,  reminding  one 
of  plus  or  positive  and  minus  or  negative  electricity,  which  exactly  neutralize 
one  another.  These  experiments  are  very  satisfactory,  and  support  greatly  the 
dynamical  theory  of  heat,  by  giving  exact  pr<  of  that  the  heat  obtained  by  the 
rapid  compression  of  air  is  almost  equal  to  the  actual  work  done. 

Professor  Rankine,  in  his  valuable  “  Manual  of  the  Steam-engine,”  examines 
the  question,  whether  latent  heat  be  a  materiality  or  not,  very  clearly.  He  says, 

“  The  term  ‘  latent  heat ,’  when  freed  from  hypothetical  notions,  means  an 
amount  of  that  condition  of  matter  called  heat  which  has  disappeared  in  pro¬ 
ducing  physical  effects  different  from  heat — such  as  expansion,  fusion,  evapo¬ 
ration,  and  chemical  changes — and  which  may  be  made  to  reappear  by  re¬ 
versing  the  changes  in  which  such  physical  effects  consisted  ;  that  is,  by  com¬ 
pression,  congelation,  liquefaction  of  vapours,  and  inverse  chemical  changes. 
The  progress  in  the  true  theory  of  thermo-dynamics,  to  which  this  discovery 
might  have  led,  was  for  a  long  time  retarded  by  a  fallacious  principle,  arising 
from  the  hypothesis  of  substantial  caloric,  in  the  following  manner: — Let  a 
substance  change  from  a  less  bulky  to  a  more  bulky  condition,  or  from 
the  liquid  to  the  gaseous  state,  or  generally  from  the  state  A  to  the  state  B, 
that  change  being  of  such  a  nature  that,  according  to  Black’s  discovery,  heat 
disappears,  and  some  physical  effect  different  from  heat  is  produced. 

“  Let  this  operation  be  called  A  B,  and  let  H,  be  the  amount  of  heat  which 
disappears. 

“  Next,  let  the  substance  change  back  from  the  state  B  to  the  original  state 
A:  let  this  change  be  called  B  A.  It  will  cause  a.  certain  quantity  of  heat, 
H„,  to  reappear.  If  the  series  of  intermediate  changes  undergone  by  the 
substance  during  the  process  B  A  be  exactly  the  reverse,  step  by  step,  with 
those  undergone  during  the  process  A  B,  everything  done  by  the  first  process 
will  be  exactly  undone  by  the  second:  no  permanent  physical  effect  will  ensue 
from  the  combined  processes ;  and  the  amount  of  heat  which  reappears,  H0, 
must  necessarily  be  equal  to  the  amount  of  heat,  H,,  which  formerly  dis¬ 
appeared.  This  was  understood  from  the  time  of  the  first  discovery  of  latent 
heat;  and  so  far  there  is  no  fallacy,  but  an  important  truth.  But  it  was  further 
assumed  that  heat  has  a  substantial  existence ,  and  that,  consequently,  H„= 
H(  under  all  circumstances,  even  although  the  processes,  A  B  and  B  A,  should 
differ  in  their  intermediate  steps.  This  assumption  leads  to  the  following 
paradoxical  result,  which  shows  it  to  be  fallacious  : — It  is  known  that  the 
process  B  A  may  be  made  to  differ  from  A  B  in  its  intermediate  steps  in 
such  a  manner  that  a  permanent  mechanical  effect  shall  be  produced  by  the 
combined  processes.  Now,  if  under  such  circumstances  H0  is  assumed  to  be 
still  =  H,,  it  follows  that,  by  employing  the  mechanical  effect  of  the  com¬ 
bined  processes  in  developing  heat  by  friction,  we  may  increase  the  amount  of 
heat  in  the  universe,  or  create  caloric — a  consequence  opposed  to  the 


STEAM. 


205 


original  assumption  of  the  substantiality  of  caloric,  and  proving  that  assump¬ 
tion  to  be  self-contradictory.” 

Further  on,  Professor  Rankine,  speaking  of  the  hypothesis  of  molecular 
vortices,  remarks  that,  “  In  thermo-dynamics,  as  well  as  in  other  branches 
of  molecular  physics,  the  laws  of  phenomena  have,  to  a  certain  extent,  been 
anticipated,  and  their  investigation  facilitated  by  the  aid  of  hypotheses  as 
to  occult  molecular  structures  and  motions  with  which  such  phenomena  are 
assumed  to  be  connected. 

“  The  hypothesis  which  has  answered  that  purpose  in  the  case  of  thermo¬ 
dynamics  is  called  that  of  ‘molecular  vortices,’  or  otherwise  the  ‘centrifugal 
theory  of  elasticity.’  On  this  subject,  see  the  ‘  Edinburgh  Philosophic 
Journal,’  1849;  ‘Edinburgh  Transactions,’  vol.  xx.,  and  ‘Philosophical 
Magazine,’  passim ,  especially  for  December,  1851,  and  November  and 
December,  1855  —  ‘  Science  of  Energetics.’  Although  the  mechanical  hypo¬ 
thesis  just  mentioned  may  be  useful  and  interesting  as  a  means  of  anticipating 
laws,  and  connecting  the  science  of  thermo-dynamics  with  that  of  ordinary 
mechanics,  still  it  is  to  be  remembered  that  the  science  of  thermo-dynamics 
is  by  no  means  dependent  for  its  certainty  on  that  or  any  other  hypothesis, 
having  been  now  reduced  to  a  system  of  principles  and  general  facts,  express¬ 
ing  chiefly  the  results  of  experiments  as  to  the  relation  between  heat  and 
motive  power. 

“  In  this  point  of  view,  the  laws  of  thermo-dynamics  may  be  regarded  as 
particular  cases  of  more  general  laws  applicable  to  all  such  states  as  con¬ 
stitute  ‘  energy ,’  or  the  capacity  to  perform  work ;  while  more  general  laws 
form  the  basis  of  the ‘science  of  energetics’ — a  science  comprehending,  as 
special  branches,  the  theories  of  motion,  heat,  light,  electricity,  and  all  other 
physical  phenomena.” 

Professor  Tait,  in  his  concise  description  of  instruments  employed  in  heat 
investigation,  sums  up  results  of  the  various  expeiiments  in  the  following 
*•  Laws  of  Thermo- Dynamics.”  1.  When  eciual  quantities  ol  mechanical  effect 
are  produced  by  any  means  from  purely  thermal  sources,  or  lost  in  purely 
thermal  effects,  equal  quantities  of  heat  are  put  out  of  existence  or  are  gene¬ 
rated  ;  and  in  the  latitude  of  Manchester,  772  foot-pounds  of  work  are  capable 
of  raising  the  temperature  of  one  pound  of  water  from  50  F.  to  51  ’  F. 

Commenting  on  this,  the  professor  remarks  that  “  Perhaps  no  purely  physi¬ 
cal  idea  has  done  so  much  to  simplify  science,  or  led  to  so  many  singular  and 
novel  predictions  (subsequently  verified  by  experiment),  as  has  Carnot’s  idea 
of  a  cycle ,  or  his  further  idea  of  a  reversible  cycle  of  operations.  It  has  given 
us  not  only  the  legitimate  mode  of  finding  the  relation  between  heat  and  work 
in  an  engine,  but  also  the  test  of  perfection  for  a  heat  engine,  an  absolute 
definition  of  temperature,  the  effect  of  pressure  on  the  melting-points  of 
solids,  and  innumerable  important  groups  of  associated  properties  of  matter 
and  energy  under  various  conditions.  ’  To  a  great  extent  these  are  included 
in  the  statement  of  the“  Second  Law  of  Thermo-Dynamics.”  If  an  engine  be 
such  that,  when  it  is  worked  backwards,  the  physical  and  mechanical  agencies 
in  every  part  of  its  motions  are  all  reversed,  it  produces  as  much  mechanical 
effect  as  can  be  produced  by  any  thermo-dynamic  engine,  with  the  same  tem¬ 
perature  of  source  and  refrigerator,  from  a  given  quantity  of  heat. 

It  is  to  be  particularly  observed  here  that  reversibility  is  the  sole  test  of  per¬ 
fection  of  an  engine  ;  also  in  the  working  of  a  reversible  heat  engine,  nothing 
is  said  about  the  nature  of  the  working  substance  :  the  temperature  of  source 


206 


HEAT. 


and  refrigerator,  and  the  quantity  of  heat  supplied,  are  the  sole  determining 
factors  of  the  work  which  can  be  done.  The  importance  of  this  proposition, 
as  regards  actual  and  proposed  engines,  cannot  be  over-estimated. 

A  cubic  inch  of  water,  converted  into  steam  under  the  ordinary  pressure  of 
the  atmosphere,  expands  into  1,696  cubic  inches,  or  nearly  one  cubic  foot. 

It  is  the  change  of  water  into  vapour,  converted  in  its  turn  into  mechanical 
motion,  which  constitutes  “energy,”  or  heat,  the  first  of  “  prime  movers,” and 
now  bringing  us  to  the  Steam  Engine. 


THE  STEAM  ENGINE. 


207 


^%-c  ,’  ^L^/J  a?/£ 


^fOC4A 


Fig.  172. — Portrait  of  Watt ,  after  Sir  IV.  Peachy ,  Watt’s  Autograph. 

ON  THE  STEAM  ENGINE. 

The  limits  of  this  work  will  not  permit  of  any  lengthened  description  of 
the  various  ingenious  extensions,  modifications,  and  improvements  ot  the 
original  and  successful  steam  engine  of  Watt — invented  and  constructed  by 
him  between  1759  and  1784.  Omitting  the  history  of  the  steam  engine  before 
the  period  of  1759,  which  the  reader  will  find  fully  described  in  the  works  of 
Tredgold,  Farcy,  Lardner,  Bourne,  and  others,  we  find,  according  to  the 
“  Memorials”  of  Watt,  carefully  collected  and  published  by  Mr.  George 
Williamson,  late  Perpetual  President  of  the  “  Watt  Club,”  of  Greenock,  that 
“it  is  in  the  little  town  of  Crawfordsdyke,  about  the  middle  of  the  seventeenth 
century  —a  small  burgh  in  the  parish  of  Greenock,  and  closely  adjoining  the 
town  of  this  name — that  we  first  meet  with  the  name  of  1  homas  \Vatt. 

“  At  what  period  of  his  life  he  jettled  here  cannot  now  be  known. 


HEAT. 


208 


“  His  object,  no  doubt,  was  to  establish  himself  in  some  locality  where  those 
branches  of  scientific  knowledge  connected  with  the  mathematics,  such  as 
astronomy  and  navigation,  might  be  rendered  available  as  a  profession.  This 
Thomas  Watt  was  the  grandfather  of  the  great  mechanician,  and  he  was 
born  during  the  civil  wars  between  Charles  I.  and  the  Parliament;  the  exact 
date  of  his  birth  appears  to  be  doubtful,  but  it  must  have  been  between 
1639  and  1642.  After  coming  to  Crawfordsdyke,  he  became  a  teacher  of  the 
mathematics  and  the  principles  of  navigation;  and  on  his  tombstone  (for 
he  died  on  the  27th  February,  1734,  aged  95)  he  is  styled  ‘Professor  of  the 
Mathematics.’ 

“  Thomas  had  two  sons,  the  elder  John  and  the  younger  James  Watt ;  the 
latter,  a  merchant  of  Greenock,  the  father  of  the  great  engineer,  was  raised  to 
office  of  bailie  or  magistrate  of  Greenock  in  the  year  1757.  He  died  in  1782, 
at  a  good  old  age,  having  attained  to  his  eighty-fifth  year.  The  flat  tombstone, 
placed  by  his  illustrious  son,  James  Watt,  records  the  deaths  of  his  father, 
mother,  and  brother,  John  Watt ;  and  the  inscription  ends  with  these  words: 

*  TO  HIS  REVERED  PARENTS, 

AND  TO  HIS  BROTHER,  JAMES  WATT 
HAS  PLACED  THIS  MEMORIAL.’ 

“  Of  the  mother  of  Watt  it  was  said  by  another  lady,  who  knew  her,  that  she 
was  1  a  braw ,  braw  woman ;  none  now  to  be  seen  like  her.' 

“  From  her  he  received  his  first  lessons  in  knowledge ;  and  although,  by  their 
very  gentleness,  he  may  have  been  rendered  doubly  sensitive  under  the  ruder 
and  more  popular  methods  of  the  public  school  to  which  he  was  afterwards 
sent,  there  is  every  reason  to  believe  that  the  very  aversion  occasioned  in  his 
mind  to  the  rough  sports  and  hard  usage  of  his  less  exquisitely  refined  play¬ 
mates  conspired  with  other  causes  to  further  rather  than  impede  the  steady 
development  of  his  future  powers.  The  truth  in  regard  to  young  Watt’s  first 
years  in  the  public  school  is,  that,  owing  doubtless  to  infirm  health,  the  suffering 
and  depression  which  affected  his  whole  powers,  he  was  unfitted  for  a  consider¬ 
able  time  for  displaying  even  a  very  ordinary  and  moderate  aptitude  for  the 
common  routine  of  school-lessons,  and  that  during  these  years  he  was  re¬ 
garded  by  his  schoolmates  as  slow  and  inapt. 

“At  thirteen  years  of  age  young  Watt,  like  that  other  giant  of  Timnath  when 
the  Philistines  were  upon  him,  woke  up  into  something  of  his  real  strength 
on  being  put  to  the  study  of  the  mathematics. 

“  This  the  author  observes  to  be  the  true  date  of  his  intellectual  birth — the 
happy  moment  when  he  took  into  his  hands  the  mystic  key  of  all  scientific 
knowledge,  with  which  in  after-years  he  was  successively  to  unlock  so  many 
of  the  secrets  of  nature,  and  lead  mankind  to  the  participation  of  some  of  her 
most  precious  treasures.” 

We  pass  on  through  the  philosopher’s  boyhood,  his  sober  pastimes,  and  his 
cultivation  of  the  learning  of  a  sage,  mathematics  and  astronomy,  until  we 
arrive  at  his  first  studies  in  the  practical  mechanics — “the  making  and  fashion¬ 
ing  of  such  miniature  pulleys  or  blocks,  pumps  and  capstans,  with  their  levers 
or  bars.”  These  objects  were  all  in  course  of  manufacture  on  his  father’s 
premises,  who  was  not  only  a  merchant,  but  a  “  master-wright,”  and  made 
such  carpentry  as  the  outfit  and  supply  of  the  shipping  demanded — gun-car- 
riages,  blocks,  pumps,  capstans,  dead-eyes ,  figure-heads,  and  the  first  “crane” 
at  Greenock,  for  the  convenience  of  “the  Virginian  tobacco-ships”  then  fre¬ 
quenting  the  harbour. 


THE  STEAM  ENGINE. 


209 


Fig.  1 73. — Boy  hoed  of  Watt. 

“A  scene  of  useful  labour  such  as  this  was  a  fitting  school  for  the  genius  of 
him  who  afterwards  was  to  become  the  leading  mechanician  of  the  day. 

“  In  clearing  out  an  attic  room  used  by  Watt  when  a  youth  in  his  twelfth 
or  thirteenth  year,  it  is  stated  by  a  late  master-shipwright  of  Greenock  that  he 
found  a  quantity  of  ingenious  models,  and  among  these  models  he  remembered 
in  particular  a  miniature  crane  and  a  barrel-organ.  Watt  is  known  subse¬ 
quently  to  have  constructed  several  musical  instruments,  particularly  an  organ 
of  some  dimensions  and  power,  while  he  was  in  Glasgow,  which,  it  is  said, 
produced  the  most  remarkable  harmonious  effects,  so  as  to  delight  even  pro¬ 
fessional  musicians;  the  more  remarkable  because  it  is  added  that  he  could 
not  distinguish  one  note  from  another,  and  was  wholly  insensible  to  the  charms 
of  music. 

“  Having  completed  his  attendance  at  the  grammar-school,  young  Watt  was 
for  a  year  or  more  industriously  occupied  about  his  father’s  premises,  either  as 
an  amateur  or  in  the  way  of  intentionally  acquiring  an  accurate  knowledge  of 
the  various  nautical  and  scientific  instruments  left  with  his  father  for  adjust¬ 
ment.  At  all  events,  he  had  a  small  forge  erected  for  his  particular.usc.  It 
is  probably  to  this  period  that  his  fabrication,  for  one  of  his  friends,  of  -a punch- 
ladle  out  of  a  large  silver  coin  is  to  be  referred. 

“In  the  year  1753,  and  after  the  death  of  his  mother  and  the  altered  cir¬ 
cumstances  of  his  father,  at  the  age  of  seventeen  or  eighteen,  he  was  sent  to 
Glasgow  to  reside  with  his  maternal  relations;  and  in  the  year  1755  went  to 
London  with  the  view  of  perfecting  himself  in  the  profession  which  it  would 
appear  the  inclination  of  the  time,  as  well  as  the  circumstances  in  which  he 
had  been  brought  up,  dictated  as  the  most  expedient. 

“  Ill  health  compelled  him  to  leave  London,  and  he  returned  to  Greenock  in 

14 


210 


HEAT. 


1756,  and  in  the  course  of  this  year  probably  settled  in  Glasgow  for  the  pro¬ 
secution  of  his  business  as  a  mathematical-instrument  maker. 

“Watt  arrived  in  Glasgow  in  his  twenty-first  year;  but  the  Corporations  of 
Arts  and  Trades,  the  Corporation  of  Hammermen, grounding  upon  their  ancient 
privileges,  looked  upon  the  young  artist  from  London  as  an  intruder,  and  obsti¬ 
nately  denied  to  him  the  right  to  open  even  the  most  humble  workshop.  Every 
means  of  conciliation  having  failed,  the  Institution  of  Glasgow  interfered, 
arranged  and  put  at  the  disposal  of  the  young  Watt  a  small  apartment  within 
its  own  buildings,  allowed  him  to  establish  a  shop,  and  honoured  him  with  the 
title  of  its  instrument  maker.  Here  the  young  mechanician  made  the  acquaint¬ 
ance,  and  then  acquired  the  sincere  friendship,  of  a  most  distinguished  and 
benevolent  man,  the  founder  of  the  Andersonian  Institution  of  Glasgow,  who, 
in  addition  to  the  labours  of  his  own  class,  which  were  strictly  academic  and 
philosophical,  instituted  a  class  and  lectures  for  workmen ,  and  for  those  whose 
pursuits  did  not  allow  of  their  conforming  to  the  prescribed  routine  of  uni¬ 
versity  studies ;  to  which  anti-toga  class,  as  he  designated  it,  he  continued 
throughout  a  long  life,  terminated  only  at  the  advanced  age  of  seventy,  to 
lecture  twice  every  week  during  the  session  of  college. 

“Such  a  man,  one  would  say,  was  eminently  he  under  whose  inspiriting  influ¬ 
ence  it  were  to  be  desired  that  the  adventurer  in  the  philosophical  instrument 
business  should  have  fallen.  It  was  Professor  Anderson  who  put  into  the  hands 
of  Watt  the  famous  model  of  Newcomen’s  engine,  which  belonged  to  the 
apparatus  of  the  professor’s  class,  and  wanted  repairing. 

“  In  his  little  university  room  Watt  now  speculated  and  experimented;  his 
workshop  became  the  resort  of  learned  professors,  as  well  as  students— ‘a 
hind  of  academy,’  says  Arago,  ‘whither  all  the  notabilities  of  Glasgow 
repaired  to  discuss  the  nicest  questions  in  art,  science,  and  literature.’  It 
was  here,  as  stated  in  the  note  appended  to  the  model  of  the  Newcomen 
engine  in  the  Hunterian  Museum  of  Glasgow,  that  ‘in  1765  James  Watt,  in 
working  to  repair  this  model,  belonging  to  the  Natural  Philosophy  Class  in 
the  University  of  Glasgow,  made  the  discovery  of  a  separate  condenser ,  which 
has  identified  his  name  with  that  of  the  steam-engine.’” 

Watt  had  accomplished  his  grand  discovery,  the  “  separate  condenser,” 
and  now  formally  registered  his  patent  for  “A  Method  of  lessening  the  Con¬ 
sumption  of  Steam,  and  consequently  of  Fuel,  in  Fire  Engines.” 

He  enrolled  in  Chancery  his  threefold  specification  of  an  effective,  work¬ 
able  steam  engine,  a  high-pressure  engine  and  a  horizontal  rotatory  engine. 
Money  (J!)  only  now  was  wanting  to  give  to  his  country  and  the  world  the  boon 
for  which  science  and  labour  were  alike  waiting.  This  was  not  denied  to 
genius  in  this  case,  because  industry  was  not  wanting.  The  young  workman 
falls  in  with  Smeaton  ;  their  histories  were  similar;  and  now  the  young  mathe¬ 
matical-instrument  maker  becomes  a  surveyor  and  civil  engineer.  Mr.  Watt 
was  next  employed  in  the  experiments  and  improvements  going  forward  at  the 
Carron  Iron  Works,  under  the  famous  Dr.  Roebuck,  who  first  defrayed  the 
expense  of  carrying  out  Watt’s  invention, 

For  a  series  of  years  prior  to  the  failure  of  Dr.  Roebuck’s  magnificent  under¬ 
takings,  and  Mr.  Watt’s  consequent  settlement,  with  the  famous  Matthew 
Boulton,  at  Soho,  near  Birmingham,  about  1774-5,  his  principal  professional 
occupations  were  those  connected  with  the  business  of  civil  engineering,  or 
surveying,  as  it  then  continued  to  be  called.  He  was  employed  in  1769  to 
survey  the  River  Clyde.  “We  see,  in  fact,”  remarks  Arago,  “  the  creator  of  an 


THE  STEAM  ENGINE. 


21  I 


engine  destined  to  form  an  epoch  in  the  annals  of  the  world  undergoing, 
without  murmur,  the  undiscerning  neglect  of  capitalists — during  eight  years 
turning  the  lofty  power  of  his  genius  to  the  getting  up  of  plans,  to  paltry 
levellings,  to  wearisome  calculations  of  excavations  and  embankments  and 
courses  of  masonry.” 

Time,  however,  works  wonders.  Watt  is  now  invited  to  join  Mr.  Boulton, 
of  Birmingham,  who  had  taken  Dr.  Roebuck's  place,  and  received  from  him 
the  most  generous  and  hearty  assistance  in  the  further  prosecution  of  the 
manufacture  of  the  steam  engine.  It  was  the  energy  of  Boulton  which  ren¬ 
dered  the  genius  of  Watt  practically  available;  and  Watt,  in  his  “  Notes  on 
the  Steam  Engine,”  says — 

“  As  a  memorial  due  to  that  friendship,  I  avail  myself  of  this,  probably  a 
last,  public  opportunity  of  stating,  that  to  his  friendly  encouragement,  to  his 
partiality  for  scientific  improvements,  and  his  ready  application  of  them  to  the 
processes  of  art,  to  his  intimate  knowledge  of  business  and  manufactures,  and 
to  his  extended  views  and  liberal  spirit  of  enterprise,  must,  in  a  great  measure, 
be  ascribed  whatever  success  may  have  attended  my  exertions.” 

Watt,  at  the  period  of  his  leaving  Scotland,  was  about  thirty-eight  or  thirty- 
nine  years  of  age;  and  “  had  Watt,”  says  Playfair,  “searched  all  Europe,  he 
could  not  have  found  another  man  so  calculated  to  introduce  the  invention 
to  the  public  in  a  manner  worthy  of  its  importance.” 

Watt,  by  the  advice  of  Bou’ton,  applied  to  Parliament  for  an  extension  of 
his  patent.  ,£50,000  had  already  been  expended  in  the  manufacture  of  engines 
and  defence  of  the  patent  by  Boulton  and  Watt  before  any  return  was  realised. 

The  extension  was  granted  for  a  term  of  twenty-five  years,  dating  from  1775. 
This  important  concession  being  secured,  Boulton  and  Watt  invited  the  utmost 
publicity.  Mechanics  and  scientific  men  crowded  to  see  the  capabilities  of  the 
new  machines.  The  Cornish  and  other  miners,  and  all  employers  of  power, 
were  shown  the  working  and  economy  of  the  new  system.  The  patentees 
themselves  said,  in  their  prospectus,  “All  that  we  ask  from  those  who  choose 
to  have  our  engines  is  the  value  of  one-third  part  of  the  coals  which  are  saved 
by  using  our  improved  machines,  instead  of  the  old.  With  our  engines  it  will 
not,  in  fact,  cost  you  but  a  trifle  more  than  half  the  money  you  now  pay  to  do 
the  same  work,  even  with  one-third  part  included,  besides  an  immense  saving 
of  room,  water,  and  expense  of  repairs. 

“The  machine  itself  which  we  supply  is  rated  at  that  price  which  would  be 
charged  by  any  neutral  manufacturer  of  a  similar  article.  And.  to  save  all 
misunderstanding,  to  engines  of  certain  sizes  certain  prices  are  affixed.. 

The  dates  of  Watt’s  inventions  are  as  follows: 

1769.  The  first  patent  involving  the  saving  of  steam  and  fuel  the  invention 
of  the  “  cutting  off  of  steam,”  to  enable  it  to  work  expansively. 

1776.  The  invention  of  the  “double-acting  steam  engine,  ’  and  the  applica¬ 
tion  of  the  crank  to  it ;  also  the  adaptation  of  this  engine  to  the  production 
of  rotatory  motion. 

1784.  Other  patents  of  invention,  viz.,  the  parallel  motion,  the  counter 
which  registered  the  strokes  of  the  engine,  the  governor,  the  throttle  valve, 
the  indicator  for  ascertaining  the  power  of  an  engine,  and  a  locomotive  engine, 
the  latter  never  practically  tested.  By  the  time  this  work  is  printed  and  circu¬ 
lated,  a  hundred  years  will  have  elapsed  since  \\  att  took  out  his  fiist  patent. 

How  many  patents  for  steam  engines  have  been  taken  out  during  that  period 
it  would  be  hard  to  say.  Every  requirement  which  steam  power  can  fulfil  i=> 

It — 2 


2  T  2 


HEAT. 


now  satisfied ;  and,  classing  the  various  forms  with  reference  to  their  purposes, 
we  find,  according  to  Rankin,  the  following  classification  : 

“  I.  Stationary  engines,  such  as  those  used  for  pumping  water,  for  driving 
manufacturing  machinery,  &c. 

“II.  Portable  engines,  which  can  be  removed  from  place  to  place,  but  are 
stationary  when  at  work. 

“III.  Marine  engines,  for  propelling  vessels. 

“  IV.  Locomotive  engines,  for  propelling  vehicles  on  land.” 

After  the  time  granted  to  Watt  by  Parliament  had  expired,  he  retired  from 
the  firm,  leaving  his  son  and  his  partner’s  son  to  continue  in  the  same  path 
of  honourable  industry. 

The  patent  expired  in  1800;  and  Watt  died  in  the  house  which  he  occupied 
at  Heathfield  during  his  sojourn  at  Soho,  on  the  23rd  of  August,  1819.  He  lies 
buried  in  the  parish  church  of  Heathfield,  at  Handsworth,  where  a  Gothic 
chapel,  containing  a  marble  statue  by  Chantrey,  was  erected  to  his  memory. 

The  next  figure  (Fig.  174),  taken  from  Walker's  “System  of  Familiar  Philo¬ 
sophy,”  published  in  1801,  will  give  the  reader  a  good  notion  of  the  con¬ 
struction  of  one  of  Watt’s  single-acting  engines,  and  what  was  even  then 
called  “  Boulton  and  Co.’s  new-invented  patent  fire  engine.” 

A.  The  boiler,  about  half  filled  with  water. 

B.  The  steam-pipe,  that  conveys  the  steam  into  the  cylinder. 

C.  The  door,  where  a  person  may  enter  to  clear  out  the  boiler. 

D.  The  loaded  or  safety  valve ;  forced  open  by  the  steam  when  too  strong, 
or  to  be  opened  by  the  handle  c. 

E.  Feeding-pipe,  from  the  warm-water  cistern  s. 

F.  Fire-door,  opening  to  the  fire  under  the  boiler. 

G.  The  ash-hole. 

H.  The  cylinder,  having  a  piston  in  it  on  the  end  of  the  rod  d ,  which  works 
through  the  air-tight  stuffing-box  o. 

I.  Nozzles,  where  the  steam  is  let  out. 

K.  Plug  frame,  to  open  and  shut  the  valves  in  its  rising  and  falling,  thereby 
suffering  the  steam  to  pass  to  the  condensing-pump  Q. 

L.  Beams  that  support  the  cylinder. 

M.  The  exhaustion-pipe,  that  conveys  the  steam  through  the  cold-water 
well  0  to  the  pump  Q. 

N.  Injection-pipe  in  the  cold  well,  to  throw  a  little  cold  water  into  the 
exhaustion-pipe  M. 

O.  The  blowing-pipe,  to  let  out  the  air  that  might  accumulate  in  the  air- 
pump  Q. 

P.  The  barometer,  to  compare  the  strength  of  the  steam  with  the  pressure 
of  the  atmosphere. 

Q.  The  air-pump,  immersed  in  a  well  of  cold  water.  When  its  piston  ascends 
by  the  chain,  it  draws  the  steam  out  of  the  cylinder,  and  condenses  it  by  the 
coldness  and  the  vacuum  in  the  pump.  The  steam  becoming  water  by  this 
means,  the  piston  descends  into  it,  the  piston-valve  is  opened  by  the  water  (as 
in  a  common  pump),  and  the  next  ascent  of  the  piston  forces  that  warm  water 
through  the  box  R,  up  the  pipe  r,  into  the  cistern  S  (which  pipe  is  cut  short  ini 
the  drawing,  but  it  begins  at  the  box  r).  This  water  supplies  the  boiler. 

R.  The  box  of  the  pipe  r. 

S.  The  cistern  of  ditto. 

T.  A  forcing-pump,  whose  solid  piston  is  forced  down  by  the  weights  s,  and 


THE  STEAM  ENGINE. 


21 3 


Fig.  174 


the  piston  of  the  cylinder  H  drawn  up.  When  the  steam  from  the  boiler 
forces  down  the  piston  of  H,  the  piston  in  T  rises,  and  rarefying  the  air  in  the 
inside  or  barrel  of  the  pump,  the  pressure  of  the  atmosphere  on  the  surface 
of  the  well  forces  up  the  water,  as  in  a  common  pump  ;  but,  by  the  descent  of 
the  piston  in  T,  the  water  is  forced  through  the  pipe  X  to  the  place  where  't  is 
wanted. 

w  is  an  air-vessel,  to  prevent  the  bursting  of  the  pipes. 

Y.  The  great  lever-beam. 

Z.  The  pipe  to  fe~d  the  condenser  cistern,  O  N  Q. 


2  T4 


HEAT. 


The  above  is  Walker’s  description  of  one  of  the  first  engines  made  by  Watt 
for  pumping  water  from  mines.  They  are  still  used  for  this  purpose  in  Corn¬ 
wall,  and  are  called  “  single-acting  engines,”  in  which  the  steam  performs  its 
work  by  its  action  on  one  side  of  the  piston  only ;  a  counterpoise  fixed  to  the 
other  end  of  the  beam  causes  the  piston  to  rise. 

Walker  finishes  his  description  by  saying,  “that  this  excellent  machine  is 
sometimes  made  to  Aork  by  the  pressure  of  steam  both  upwards  and  down¬ 
wards ;  i.e.,  the  steam  can  be  made  to  press  the  piston  up,  as  well  as  down. 
This  adds  considerably  to  the  first  expense  and  the  continued  expense  of  fire.” 

This  Cornish  engine,  made  by  Watt,  is  a  singular  contrast  to  the  engines  ot 
the  present  day,  in  which  the  consumption  of  fuel,  and  consequently  the  work 
performed,  is  carried  to  the  most  refined  and  absolute  degree  of  perfection. 
Engines  have  been  made  to  perform  the  duty  of  raising  one  hundred  million 
pounds  of  water  one  foot  high  by  the  consumption  of  a  single  bushel  of  coals. 

The  essential  portions  of  the  steam  engine  are  better  studied  in  Watt’s 
“  Double-action  Engine.”  In  this,  as  in  t-he  single-acting  engine,  the 
“  cylinder”  holds  the  first  place. 

This  consists  of  a  cylinder  of  metal,  A  D,  provided  with  a  piston,  B,  the  end 
of  which  passes  through  a  stuffing-box,  c,  and  is  connected  with  the  beam  by  a 

beautiful  arrangement  called  the  parallel  mo¬ 
tion  (Fig.  177).  The  steam  is  passed  into  this 
cylinder  both  above  and  below  the  piston  with 
the  utmost  regularity,  by  means  of  a  sliding 
valve,  E.  This  valve  opens  a  communication 
between  the  interior  of  the  boiler  and  the 
cylinder,  and  the  condenser  and  the  cylinder, 
in  such  a  manner  that,  whilst  the  steam  is 
using  its  power  on  one  side  of  the  piston,  it  is 
at  the  same  time  creating  a  vacuum  on  the 
other  side,  by  passing  into  a  box  called  the 
condenser,  F — the  famous  '•'‘separate  con¬ 
denser”  of  Watt — to  which  an  air-pump  is 
attached  to  remove  any  air  that  may  collect, 
the  condensed  water,  and  also  that  used  for 
injection. 

The  sliding  of  the  valve  upward  and  down¬ 
ward  is  effected  by  means  of  another  admi¬ 
rable  mechanical  arrangement,  called  the 
“  eccentric.” 

In  nearly  every  kind  of  engine  there  is 
attached  to  the  beam  and  piston-rod  a  “  pa¬ 
rallel  motion,”  in  order  that  the  piston-rod 
may  always  move  in  a  straight  line.  This 
simple  mechanical  arrangement  is  one  of  the 
happiest  of  the  inventions  which  seem  to 
have  come,  as  it  were  intuitively  to  the  well' 
educated  mind  of  Watt. 

To  render  the  working  of  the  double-acting 
engine  as  perfect  as  possible,  and  to  prevent 
the  bad  effects  of  sudden  and  violent  work¬ 
ing  by  excess  of  steam.  Watt  caused  his  engine  to  regulate  its  own  motion  by 


Fig.  175. —  The  Cylinder , 
Valve,  and  Condenser 


THE  STEAM  ENGINE. 


Fig.  176. — The  Eccentric. 

what  is  called  the  “governor.”  This  was  not  wholly  the  invention  of  Watt, 
as  the  same  principle  had  been  previously  used  in  the  regulation  of  sluices  of 
Water-mills,  under  the  name  of  the  “lift-tenter;”  but  the  merit  due  to  Watt  is 


Fig.  177. —  The  Parallel  Motion . 

&  a,  the  beam ;  b,  the  piston-rod  ;  c,  the  air-pump  rod  ;  d  d  d,  the  links ;  t,  rod  fixed  to  the  Cylinder 

to  support  the  guiding  arm  or  radius  rod,/. 

that  of  accurately  adjusting  the  contrivance  to  the  opening  and  shutting  of  the 
steam-pipe  from  the  boiler  by  a  valve  called  the  “  throttle  valve,  ’  so  that  \\  hen 
the  engine  is  inclined  to  go  fast,  and  use  too  much  steam,  the  balls  of  t  ie 
governor  fly  out  by  centrifugal  force,  and,  acting  on  the  throttle  van  e,  the 
steam  is  cut  off,  and  the  velocity  of  the  engine  reduced. 


2l6 


HEAT 


Fig.  178. —  The  Governor  and  Throttle  Valve ,  as  used  in  a  2\  horse-power 
High-pressure  Steam  Engine ,  by  Beiliss  <3^  Seekings ,  Great  Exhibition ,  1 862. 


The  governor  in  the  above  engine  acts  upon  an  equilibrium  or  double¬ 
beat  throttle  valve,  through  the  intervention  of  only  a  single  lever ;  and  the 
comparative  absence  of  resistance  renders  its  action  peculiarly  sensitive. 

The  most  important  features  of  the  “  vacuum  ”  or  “  condensing  engine  ”  of 
Watt  having  been  discussed,  the  high-pressure  steam  engine,  such  as  that 
delineated  at  Fig.  178,  may  next  be  considered.  Their  form  is  legion  ;  they 
may  be  beam  engines  or  horizontal  or  vertical  engines.  The  machinery 
comprised  in  their  construction  can  be  fitted  up  in  a  much  smaller  space  ; 
and  they  differ  from  the  “vacuum  or  condensing  engine”  by  the  absence  of 
those  parts  which  give  the  name  to  Watt’s  engine.  The  air-pump  and  condenser 
are  removed,  and  the  steam,  after  performing  its  work,  is  allowed  to  escape 
directly  into  the  atmosphere.  An  illustration  of  a  small  engine  is  given, 
because  the  high-pressure  principle  is  well  adapted  for  nearly  all  small 


THE  STEAM  ENGINE. 


217 


engines,  and  it  is  especially  to  be  noted  in  the  locomotive.  Portable  engines, 
which  can  be  removed  from  place  to  place,  but  are  stationary  when  at  work, 
are  all  worked  on  the  high-pressure  principle.  At  the  great  French  Exhibi¬ 
tion  of  1867,  English  manufacturers  of  portable  steam  engines  for  agricul¬ 
tural  purposes,  such  as  for  working  thrashing-machines,  ploughing,  &c., 
received  many  more  gold  medals  than  those  of  other  nations  ;  and  the  excel¬ 
lence  of  the  machinery  used  by  advanced  and  intelligent  farmers  in  England 
has  created  a  trade  with  foreign  countries  which,  in  spite  of  the  low  wages  of 
the  engineers  of  the  Continent,  is  still  most  thriving  and  lucrative. 


FlG.  179. — Howard's  Patent  Steam  Ploughing  and  Cultivating  Apparatus. 


The  apparatus  delineated  in  the  above  engraving  includes  the  engine,  the 
windlass,  the  wire  rope,  the  cultivator,  the  anchors,  and  pulleys.  'I  he  young 
people  for  whom  this  book  is  intended  have  so  many  opportunities  of  studying 
the  locomotive  engine  at  the  various  railway  stations,  that  it  is  presumed  the 
general  outline  of  this  most  important  class  of  engines  must  be  sufficiently 
known  to  all. 

The  interior  of  a  locomotive  can  hardly  be  thoroughly  understood  without 
one  of  those  valuable  sectional  models  made  by  various  manufacturers  for  the 
use  of  schools.  The  models  have  sectional  working  gear,  and  accurately 
define  the  various  parts  .and  their  respective  uses;  and  all  good  schools  should 
possess  sectional  models  of  the  Watt  condensing  engine  and  of  the  locomo¬ 
tive  or  high-pressure  engine.  , 

At  the  Exhibition  of  1862  was  exhibited  a  locomotive  engine,  built  for  the 
London  and  North-Western  Railway  Company  by  Mr.  Ramsbottom,  their 
locomotive  superintendent,  at  Crewe,  being  a  good  specimen  of  a  first-class 
passenger  engine.  It  was  fitted  with  patent  pistons,  duplex  safety-valves,  and 
lubricators,  and  adapted  for  burning  coals  with  great  economy. 

An  engine  of  this  class  ran  the  American  express,  on  the  7th  January, 
'862.  a  distance  of  130^  miles  without  stopping ,  at  an  average  speed  ol  54 


2  I  8 


HEAT. 


—  — 

L/As 

0]  / 

A  ib=\i 

0  / 

Fig.  180. — Apparatus  for  Supplying  Water  to  Tenders  whilst  in  motion. 


miles  per  hour.  The  tender  attached  (Fig.  180)  was  fitted  with  Mr.  Rams- 
bottom’s  most  ingenious  apparatus  for  taking  up  water  whilst  running. 
The  plan  has  been  in  daily  operation  on  the  Chester  and  Holyhead  Railway 
since  it  was  first  adopted  in  the  winter  of  1859-60.  By  it  various  quantities 
of  water,  from  1,200  gallons  downwards,  can  be  picked  up,  at  speeds  ranging 
from  22  miles  to  50  miles  and  upwards  per  hour.  In  the  running  of  the  Irish 
mails,  the  arrangement  has  the  effect  of  reducing  the  dead  weight  of  the 
tender  about  six  tons,  equal  to  the  weight  of  a  loaded  carriage. 

These  engines  are  added  to  the  enormous  screw  engines  manufactured  by 
Messrs.  James  Watt  &  Co.  The  latter  consist  of  four  cylinders,  each  of  84 
inches  diameter. 

The  paddle-wheels  are  driven  by  four  engines,  each  of  72  inches  diameter 
of  cylinder  and  14  feet  stroke,  and  rated  collectively  at  1000  nominal  horse¬ 
power. 

In  the  Exhibition  of  1862  some  good  examples  of  high  and  low  pressure 
marine  condensing  engines,  with  surface  condensers,  were  shown  by  George 
Rennie  &  Son. 

The  advantage  of  two  cylinders  in  direct-acting  marine  screw  engines  is 
that  of  working  steam  expansively,  whereby  economy  of  steam  and  fuel  is 
obtained,  depending  on  the  pressuie  of  the  steam  and  the  relative  volumes  of 
the  high  and  low  pressure  cylinders.  These  engines  are  fitted  with  surface 
condensers,  with  copper  tubes  and  improved  centrifugal  pumps  for  circulating 
the  water  in  the  condensers,  these  pumps  being  made  on  a  double-curvature 
principle  of  least  resistance  to  the  flow  of  water  occasioned  by  the  centrifugal 
force  generated  by  the  angular  velocity  of  the  pump. 

Engines  on  this  principle  are  fitted  with  boilers  in  proportion.  Apparatus 
for  superheating  steam  and  feed-water  heaters  may  be  made  to  consume  not 
more  than  two  pounds  of  coal  per  actual  horse-power. 

The  important  principle  of  working  steam  expansively  has  been  applied 


Fig.  i  8  i. —  The  Paddle-Wheel  Engines  of  the  Great  Eastern. 


with  the  greatest  success  in  large  engines,  made  like  the  Cornish  ones,  for 
pumping  enormous  quantities  of  water  for  the  use  of  great  cities  like  London. 

Steam  of  high  pressure  is  used,  and  when  admitted  to  the  piston  it  is  cut 
off  at  one-eighth  or  one-tenth  of  the  stroke.  At  the  Kent  Waterworks  the 
Cornish  engines  used  are  two  with  cylinders  of  70  inches  and  10  feet  stroke, 
two  with  cylinders  of  60.  inches,  and  two  smaller  ones  ;  in  these  engines  the 
expansion  was  not  more  than  one-fifth.  The  high-pressure,  condensing, 
double-cylinder  engines  erected  at  Ditton  for  the  Lambeth  Waterworks,  and  at 
Kingston  for  the  Chelsea  Waterworks  Company,  can  accomplish,  according 
to  Mr.  Simpson,  in  ordinary  work,  90  million  pounds  raised  1  foot  high  per 
one  hundredweight  of  coals  consumed. 

The  returns  of  the  work  performed  by  the  Cornish  pumping  engines  have 
been  given  from  an  early  date,  and  are  very  interesting. 

1769,  John  Taylor  gave  the  return  at  only  5^  millions.  • 

In  1800  20  „ 

,,1815  .  .  5°  » 

„  1835  .  .125 

The  latter  125  millions  was  at  Fowey’s  Consols  Mine,  where  Austen  s  engine 
was  used.  It  might  almost  be  disputed  whether  such  an  amount  of  duty  was 
ever  done;  but  it  was  well  authenticated  by  the  report  of  the  committee  ap¬ 
pointed,  and  they  reported  that  the  work  was  done  with  a  bushel  of  coals, 
weighing  94  pounds. 


220 


HE  A  2: 


The  principle  of  expansion  was  used  by  Watt,  but  without  any  very  good 
result ;  but  Woolf  and  Trevithick  applied  the  system  with  high-pressure 
steam,  and  realised  the  economical  results  already  referred  to.  With  respect 
to  the  double-cylinder  engine,  this  was  invented  by  Jonathan  Hornblower, 
and  not  by  Watt.  It  was  patented  by  the  former  in  1781.  The  first  and 
second  patents  of  Hornblower  contain  the  following 

“  First,  1  use  two  vessels  in  which  the  steam  is  to  act,  and  which  in  other 
steam  engines  are  generally  called  cylinders. 

“  Secondly,  I  employ  the  steam,  after  it  has  acted  on  the  first  vessel,  to 
operate  a  second  time  on  the  other,  by  permitting  it  to  expand  itself,  which  I 
do  by  connecting  the  vessels  together,  and  forming  proper  channels  and 
apertures,  whereby  the  steam  shall  occasionally  go  in  and  out  of  the  same 
vessel.” 

I'he  third  invention  was  for  “  surface  condensation,”  a  term  already  used, 
and  meaning  the  application  of  cold  water  on  the  other  side  of  a  plate  forming 
the  side  of  the  box  containing  the  steam.  The  more  perfectly  the  circulation  of 
the  cold  water  can  be  maintained,  the  better  is  the  condensation.  A  surface- 
condenser  represents  the  worm  attached  to  a  common  still,  and  this  invention 
evades  the  “  separate  condenser”  in  the  patent  of  Watt. 


Fig.  182. — A  Cornish  Boiler. 


Professional  men  have  discussed  the  respective  merits  of  the  single  and 
double  cylinders,  and  Mr.  Hawksley  stated,  as  the  result  of  his  experience, 
“  that  when  raising  water  from  a  pit,  the  Cornish  engine  (single  cylinder) 
would  work  well ;  but  it  would  perform  best  when  pumping  out  of  a  deep  pit, 
and  when  it  had  a  large  amount  of  heavy  rods  to  continue  its  action  and 
diminish  its  initial  velocity.  In  the  case  of  dear  coal  he  would  employ  the 
double  cylinder  ;  in  the  case  of  cheap  coal  he  would  employ  the  sin  ;le 
cylinder  ;  and  either  not  cut  off  the  steam  at  ail,  or  not  much  before  it  gets  to 
the  end  of  the  stroke. 

With  the  double  cylinder  he  would  use  eight  expansions ;  beyond  that,  so 
little  was  gained  by  rhe  system  of  expanding  steam,  that  it  was  not  worth 
carrying  it  further. 

In  order  to  economise  coal,  and,  of  course,  to  increase  the  stowage  qualities 


EVAPORATION. 


221 


of  a  vessel,  the  “  Combined  Vapour  Engine”  was  invented  by  M.  du  Trembley. 
This  ingenious  arrangement  provided  that,  after  the  steam  had  done  its  work 
in  the  cylinder,  it  passed  to  the  surface-condenser,  which  was  surrounded 
with  ether,  and,  causing  this  fluid  to  boil,  the  vapour  passed  to  another 
cylinder,  where  it  exerted  its  elastic  force;  and  after  the  vapour  of  the  ether 
had  done  its  work,  it  was  finally  condensed  and  pumped  back  again  to  the 
box  surrounding  the  external  condenser  of  the  steam  engine,  the  condensa¬ 
tion  of  the  vapour  of  water  causing  another  fluid  (ether)  to  boil.  This*  clever 
arrangement  met  with  considerable  approval,  and  has  been  tried  on  an  exten¬ 
sive  scale  in  the  propulsion  of  vessels. 

Superheated  steam,  or  steam  passed  through  a  coil  of  iron  pipe  placed  in 
the  furnace,  has  been  proposed  and  used  successfully  in  the  working  of  marine 
engines  in  order  to  economise  fuel  Rankin  calls  this  superheated  steam 
“steam-gas  and  the  Hon.  John  Wethcrcd,  of  the  United  States,  modified 
this  superheated  steam  by  mixing  it  with  ordinary  steam  from  the  boiler, 
because  he  found  that  when  the  steam  was  heated  sufficiently  high  to  develop 
the  full  power,  it  destroyed  the  cylinder  and  slides.  He  considers  the  differ¬ 
ence  between  superheated  steam  and  combined  steam  consists  in  this— that 
the  former,  being  of  a  gaseous  nature,  was  a  bad  conductor  of  heat,  and  parted 
with  it  with  difficulty  ;  whereas  combined  steam,  being  pure  vapour  and  a 
better  conductor  of  heat,  parted  with  it  more  readily,  and  left  more  in  the 
cylinder  of  the  engine  to  be  converted  into  mechanical  power. 

Wethered  claimed  an  economy  of  combined  steam  over  ordinary  steam  of 
52*5  per  cent.,  and  over  superheated  steam  of  25  per  cent.  According  to 
more  recent  experiments  on  the  large  scale,  made  by  the  eminent  firm  of 
Messrs.  Penn,  of  Greenwich,  with  superheated  steam,  it  is  conclusively 
determined  that  an  economy  of  20  per  cent,  of  fuel  was  realized  in  the  working 
of  marine  engines,  when  the  steam  at  a  pressure  of  20  pounds  per  square  inch 
was  raised  by  the  superheating  apparatus  ioo°  Fahrenheit. 

The  Cornish  boiler,  to  which  allusion  in  connection  with  the  Cornish 
engine  has  already  been  made,  is  shown  at  Fig.  182.  It  consists  of  a  double 
cylinder,  the  fire  being  placed  on  bars  inside  it,  and  is  one  of  the  most 
useful  forms  that  can  be  employed,  and  is  the  kind  of  boiler  used  for  working 
the  steam  engine  at  the  Polytechnic. 


- - 

EVAPORATION. 

It  is  so  common  an  act  to  boil  water  and  convert  it  into  steam,  that  non- 
scientific  minds  are  sometimes  puzzled  when  the  more  learned  talk  of  steam,  or 
the  vapour  of  water,  being  always  present  in  the  air  we  breathe;  they  begin  to 
ask  themselves  mentally  for  the  visible  presence  of  great  cauldrons  of  boiling 
water  to  supply  the  vapour ;  and,  failing  these  proofs,  subside  into  a  sort  ot 
wondering  doubt. 

The  great  evaporating  surfaces  of  the  oceans,  rivers,  lakes,  &c.,  are  always 
silently  at  work  ;  and  Faraday,  in  one  of  his  popular  discourses,  said  that  sixty 
sacks  of  coal  must  be  burnt  to  produce  an  amount  of  steam  such  as  would 
pass  away  gradually  from  the  surface  of  an  acre  of  ground  during  an  ordinary 

summer’s  day.,  ....  , 

The  proof  that  the  atmospheric  air  does  contain  invisible  steam  is  shown 


222 


HEAT 


by  the  water  deposited  outside  a  tumbler  containing  iced  water,  or  water  drawn 
from  a  deep  well  a  few  degrees  below  the  temperature  of  the  air. 

Evaporation  is  confined  to  the  surface  of  the  liquid  exposed  to  the  air;  and 
that  may  be  stopped,  as  in  the  case  of  water  when  oil  is  poured  upon  it. 

If,  during  evaporation,  vapour  forms  under  the  ordinary  pressure  of  the 
air,  it  is  necessarily  increased  when  produced  in  a  vacuum,  because  there  is 
no  resistance  to  be  overcome ;  as  the  first  is  the  slow  production  of  vapour  at 
the  surface  of  a  liquid,  so  the  second  is  the  quick  production  of  vapour. 

If  a  number  of  barometer-tubes  are  filled  with  mercury,  and  placed  in  a 
proper  vessel  or  trough,  also  containing  mercury,  they  all  exhibit  a  height  cor¬ 
responding  to  the  existing  pressure  of  the  air;  when,  however,  a  few  drops  of 
water,  alcohol,  or  ether,  or  a  small  lump  of  ice,  are  introduced  respectively 
into  the  separate  tubes,  the  mercury  is  depressed  immediately,  showing  the 
evaporation  which  instantaneously  takes  place  in  the  Toricellian  vacuum,  or 
space  above  the  level  of  the  mercury  in  the  barometer. 


The  amount  of  depression,  showing  the  elastic  force  of  the  vapour,  varies 
with  each  liquid.  At  the  same  time,  the  above  experiment  shows  that  all  vola¬ 
tile  liquids  are  instantaneously  converted  into  vapour  in  a  void  space,  or 
vacuum. 

Faraday  found  that  there  was  a  limit  even  to  evaporation,  and,  experi¬ 
menting  with  mercury,  he  noticed  that  a  slip  of  gold  leaf,  suspended  in  the 
neck  of  a  bottle  containing  mercury,  was  whitened  by  the  evaporation  and 
condensation  of  the  quicksilver  upon  the  gold.  This  effect  did  not,  however, 
take  place  at  a  temperature  of  about  39‘2°  F.  With  sulphuric  acid,  which 
is  a  very  permanent  fluid,  the  temperature  of  the  limit  of  evaporation  was 
found  to  be  much  higher,  viz.,  about  86°  F. 

Various  instruments  have  been  devised,  from  the  earliest  times  of  scientific 
investigation,  to  determine  the  quantity  of  invisible  steam  or  moisture  in  the 
air.  All  cords,  and  especially  catgut  (a  string  made  from  the  peritoneal  linings 
of  the  intestines  of  the  sheep;,  lengthen  or  shorten  according  to  the  state  of 
the  moisture  in  the  air. 

If  a  piece  of  catgut,  made  fast  at  one  extremity,  be  conveyed,  as  in  Fig. 


HYGROMETRY. 


223 


183,  over  a  series  of  pulleys,  A,  B,  c,  D,  E,  F,  G,  so  as  to  make  several  turns 
backwards  and  forwards,  and  if  a  weight,  P,  be  suspended  from  the  other 
extremity,  the  latter  will  fall  as  the  string  lengthens  in  damp  weather,  and 
rise  as  the  air  becomes  drier.  This  is  shown  better  by  attaching  an  index 
or  pointer,  H  K,  turning  on  a  pivot  I,  in  such  a  manner  that  the  length  I  K 
shall  be  greater  than  1  H,  and  pointing  to  a  graduated  arc,  L  L. 

Saussure  employed  a  human  hair  for  the  same  purpose;  but  all  such  arrange¬ 
ments  infallibly  become  deteriorated  by  time. 

M.  Le  Roi  was  the  first  to  suggest  that  the  temperature  at  which  dew  begins 
to  be  deposited  should  be  employed  as  the  measure  of  the  moisture  of  the 
air.  De  Luc  also  proved  that  the  quantity  and  force  of  vapour  in  vacuo  are 


FlG.  184. — Regnault’s  Condensing  Hydrometer,  by  Negretti  and  Zambra. 

the  same  as  in  an  equal  volume  of  air  of  the  same  temperature,  or  that  these 
two  elements  of  vapour  depend  upon  the  temperature. 

The  determination  of  the  exact  temperature  at  which  dew  is  formed,  and  at 
which,  in  the  open  air,  the  dew  disappears  or  ceases  to  be  formed  on  the  sides 
of  the  vessel  producing  it,  is  of  the  utmost  importance,  and  was  carefully 
investigated  by  the  late  I)r.  Dalton.  The  observation  is  rendered  more  exact 
with  a  bright  metallic  vessel,  as  in  Regnault’s  elegant  apparatus. 

Regnault’s  Condenser  Hygrometer  consists  of  two  highly  polished  smer 
cylinders,  into  the  upper  part  of  which  are  cemented  thin  glass  tubes  ;  these 
have  brass  covers,  arranged  to  receive  and  support  two  delicate  standaid 
thermometers,  the  bulbs  of  which  descend  nearly  to  the  bottom  of  the  siheu 
portion  of  these  chambers.  Each  chamber  has  a  small  internal  tube  carritu 


224 


HEAT. 


down  from  the  brass  to  within  a  short  distance  of  the  bottom,  to  admit  the 
passage  of  the  air,  which  is  drawn  through  both  chambers  by  an  aspirator, 
connected  to  the  base  of  the  hollow  upright  and  arms  supporting  the  cylinders. 
To  use  this  hygrometer,  ether  is  poured  into  one  chamber  sufficient  to  cover 
the  bulb  of  the  thermometer,  and  then  the  thermometers  being  inserted  into 
both  cylinders,  the  instrument  is  now  connected  to  the  aspirator,  and  by  it  the 
air  is  drawn  through  both  cylinders  down  the  internal  tubes,  passing  in  one 
chamber  in  bubbles  through  the  ether,  and  in  the  other  chamber  simply  around 
the  thermometer.  The  tube  in  this  empty  cylinder  is  of  such  a  diameter  as  to 
ensure  similar  quantities  of  air  passing  through  each  chamber. 

After  a  short  time  the  passage  of  the  air  through  the  ether  will  cool  it  down 
to  the  dew-point  temperature,  and  the  external  portion  of  the  silver  chamber 
containing  the  ether  will  become  covered  with  moisture.  The  degree  shown 
by  the  thermometer  in  the  ether  at  that  instant  will  be  the  temperature  of  the 
dew-point ;  the  second  thermometer  showing  the  temperature  of  the  air  at  the 
time  of  observation. 

The  late  Professor  Daniell,  who  paid  much  attention  to  the  construction  of 
hygrometers,  and,  indeed,  constructed  one  of  the  best  and  most  simple,  says: 

“  The  more  accurate  mode  of  expressing  the  moisture  of  the  air  from  an 
observation  of  the  temperature  and  dew-point  is  by  the  quotient  of  the  divi¬ 
sion  of  the  elasticity  of  vapour  at  the  real  atmospheric  temperature  by  the 
elasticity  at  the  temperature  of  the  dew-point;  for,  calling  the  term  of  satura¬ 
tion  1000,  as  the  elasticity  of  vapour  al  the  temperature  of  the  air  is  to  the 
elasticity  of  vapour  at  the  temperature  of  the  dew-point,  so  is  the  term  of 
saturation  to  the  observed  degree  of  moisture.  Thus,  with  regard  to  the  obser¬ 
vation  in  the  Deccan,  where,  with  a  temperature  of  90°  F.,  the  dew-point  has 
been  seen  as  low  as  29°,  making  the  degree  of  dryness  61. 

Force  at  90°.  Force  at  290. 

1 ‘430  o  194  1000  :  135 

The  fourth  term  is  the  degree  of  moisture  on  the  hygrometric  scale.” 

- ♦ - 

RADIATION. 

It  is  not  at  all  surprising  that  the  philosophers  who  first  commenced  experi¬ 
ments  with  heat,  or  caloric,  should  have  regarded  it  as  an  imponderable  and 
highly  elastic  fluid,  which  clothed,  as  it  were,  the  material  particles  of  solids, 
fluids,  and  gases ;  the  latter  attracting  the  former,  and  sometimes  emitting 
or  throwing  out  their  caloric,  which  was  also  supposed  to  be  repulsive  of  its 
own  particles.  The  material  theory  of  heat  is',  however,  not  tenable :  when 
we  consider  it  as  radiant  matter,  we  are  reminded  at  once  of  its  analogy  to 
light,  and  we  understand  that  the  undulations  of  the  same  ethereal  medium 
may  propagate  heat  as  well  as  light :  it  is  not  necessary  to  suppose  that  the 
ether  which  gives  us  light  is  interpenetrated  by  another  kind  of  ether  that 
may  give  us  heat.  The  examination  of  the  invisible  heat  rays  in  the  solar 
spectrum  assist  us  greatly  in  taking  a  correct  view  of  the  phenomena. 

Whilst  enjoying  the  social  pleasures  of  the  fireside,  we  are  always  reminded 
that  heat  can  travel,  like  light,  through  space. 

At  night,  if  travelling  in  a  steamboat  across  the  Channel,  we  approach  the 
funnel,  from  which  invisible  heat  is  constantly  radiating,  we  see  no  fire,  and 


RADIATION. 


225 


yet  we  can  understand  by  the  pleasant  warmth  experienced  that  waves  of 
heat  may  be  impinging  upon  us,  just  as  the  waves  of  water  dart  against  the 
sides  of  the  vessel.  We  shall  find  presently  that  light-waves  may  be  sepa¬ 
rated  from  heat-undulations ;  and  even  when  they  travel  together,  and  the 
light  only  is  apparent,  the  heat  may  be  rendered  evident  in  various  ways,  as 
in  the  use  of  the  burning-glass,  or,  by  permitting  the  rays  of  the  sun  to  pass 
through  a  glass  containing  some  ether,  the  rays  are  freely  transmitted,  but  if 
a  piece  of  charcoal  is  placed  in  the  ether,  the  heat  rays  are  arrested,  and 
vibratory  power  is  soon  conferred  upon  the  charcoal,  which  in  its  turn  com¬ 
municates  motion  to  the  ether,  and  raises  it  to  the  boiling-point. 

The  intensity  of  the  heat  rays  decreases  or  increases  according  to  the  same 
law  which  affects  light,  viz.,  as  the  square  of  the  distance  inversely.  The  in¬ 
tensity  of  heat  is  less,  the  greater  the  obliquity  of  the  rays  vVith  respect  to 
the  radiating  surface.  Avoiding  a  source  of  heat  which  may  be  accompanied 
with  light,  and  using  a  canister  filled  with  boiling  water,  and  placing  it  in  the 
focus  of  a  polished  concave  metallic  reflector,  the  rays  are  collected,  and  can 
be  thrown  off  to  another  reflector,  when  they  are  again  brought  to  a  focus, 
discoverable  by  an  air-thermometer  (p.  147.) 

At  the  Polytechnic  a  small  bit  of  meat  can  be  cooked  when  placed  in  the 
focus  of  a  large  concave  reflector,  and  opposite  to  another  standing  100  ft.  away, 
and  containing  in  its  focus  a  large  wire  cage  full  of  burning  charcoal. 


Fig.  185. —  The  large  Polytechnic  Metallic  Reflectors. 
A  fire  in  the  focus  of  one,  and  the  meat  in  the  focus  of  the  other. 


The  power  of  reflecting  heat  ray's  is  influenced  by  the  condition  of  the  sur¬ 
face.  Polished  metals  possess  the  property  in  the  highest  degree;  and  if  the 
bit  of  meat  were  covered  with  gold  leaf  it  would  not  be  warmed  through, 
whilst  the  opposite  effect  of  first  blackening  the  meat,  by  dusting  finely 
powdered  charcoal  over  it,  assists  the  absorption  of  the  heat  rays  very  greatly. 
Melloni  discovered  that  out  of  too  rays 

Silver . reflects  90 

Bright  lead  ....  „  6° 

Glass  .....  „  10 

Hence,  if  a  glass  concave  mirror  is  used  to  reflect  the  rays  of  an  ordinary 
fire  towards  the  face,  little  or  no  warmth  is  experienced  ;  on  the  other  hand,  a 
concave  tin  plate  will  reflect  the  heat  very  sensibly. 

lb 


226 


HEAT. 


It  was  formerly  supposed  that  the  power  of  a  body  to  absorb  heat  was  in 
dre  inverse  proportion  of  its  power  to  throw  off  or  reflect  heat — that  the  two 
properties  exactly  accounted  for  the  heat  originally  falling  upon  any  given 
surface.  This,  however,  is  not  found  to  be  the  case.  The  heat  waves  which 
are  incident  upon  any  given  surface  are  disposed  of  in  three  ways: 

I.  Some  portion  is  absorbed. 

II.  Another  portion  is  reflected  according  to  the  ordinary  laws  which 
govern  the  reflection  of  light. 

/II.  A  third  portion  is  scattered,  and  is  then  called  diffused  heat. 

The  thinnest  film  of  gold  leaf  will  protect  the  parts  of  a  sheet  of  paper 
exposed  to  radiation  from  some  red-hot  surface,  whilst  the  blackening  of  any 
portion  of  the  same  sheet  of  paper  will  hasten  its  destruction. 

Radiation  and  absorption,  according  to  the  experiments  of  Leslie,  are 
directly  proportioned  to  each  other;  a  blackened  tin  vessel  full  of  hot  water, 
that  will  radiate  heat  freely,  and  soon  fall  to  the  temperature  of  the  air,  will, 
on  the  other  hand,  as  rapidly  increase  in  temperature  if  held  near  any  good 
source  of  heat. 

The  relation  between  radiation,  absorption,  and  reflection,  and  the  manner 
in  which  the  two  first  may  balance  each  other,  was  elegantly  shown  by  the 
late  Dr.  Ritchie.  He  used  for  his  experiments  a  metallic  vessel  filled  with  hot 
water,  and  a  differential  thermometer,  one  bulb  of  which  was  shielded  by  a 
bright  metallic  disc,  and  the  other  with  a  blackened  one;  one  surface  of 
the  metallic  box  containing  the  water  was  also  polished,  and  the  other 
blackened.  When  the  blackened  side  of  the  box  was  placed  opposite  to  the 
bright  metallic  screen,  no  effect  was  produced  on  the  thermometer,  because 
the  radiating  power  of  the  black  surface  was  neutralized  by  the  non-absorp- 
tive  and  good  reflecting  power  of  the  bright  metallic  disc.  If,  however,  the 
same  side  was  opposed  to  the  blackened  disc,  then  the  thermometer  was 
affected.  Similarly,  but  reversely,  when  the  polished  side  of  the  box  was 
opposed  to  the  blackened  disc,  little  or  no  effect  was  perceptible,  because  the 
highly  polished  surface  did  not  radiate  heat  easily. 

If  boiling  water  be  poured  into  two  tea-pots,  one  of  which  is  of  bright 
block  tin,  and  the  other  of  black  japanned  tin,  the  latter  cools  more  quickly 
than  the  former. 

The  air  exercises  a  retarding  power  on  the  waves  of  heat  which  are  absorbed, 
and,  as  proved  by  Sir  H.  Davy,  they  travel  much  easier  through  a  vacuum. 
Davy  ignited  charcoal  points  by  a  current  of  electricity,  and,  placing  them  in 
the  focus  of  a  concave  mirror,  discovered  that,  when  the  receiver  was  exhausted 
to  i-i2oth,  the  effect  upon  a  thermometer  placed  in  the  focus  of  another  reflector 
was  nearly  three  times  as  great  as  when  the  air  was  at  its  ordinary  pressure. 

The  absorptive  power  of  bodies  was  supposed  to  depend  greatly  upon  the 
particular  colour  used.  Franklin  placed  pieces  of  coloured  cloth  in  the 
sun’s  rays  on  the  snow,  and  found  they  sank  into  the  snow  or  melted  it  in  the 
following  order: — black,  blue,  green,  purple,  red,  yellow,  white.  Tyndall,  how¬ 
ever,  has  explained  the  cause  more  correctly,  and  has  discovered  that  the 
colour  has  not  so  much  to  do  with  the  effect  produced  as  the  nature  of  the 
material  used  for  the  colouring  agent.  Although  it  has  been  stated  by  Leslie 
that  white  surfaces  generally  reflect  heat  well,  and  absorb  it  indifferently, 
there  is  the  curious  fact,  ascertained  by  Melloni,  that  white  lead  has  quite  as 
great  an  absorbent  power  as  lampblack;  and  if  the  heat  comes  from  boiling 
water  (column  i),  it  will  absorb  twice  as  much  as  it  would  do  if  it  came  from  an 


RADIATION. 


227 


incandescent  platinum  wire.  Melloni  (p.  201)  filled  a  copper  canister  with  water, 
and  kept  it  at  the  boiling-point,  and  by  means  of  a  very  delicate  instru¬ 
ment,  called  the  thermo-multiplier,  obtained  the  following  relative  absorptive 
powers,  as  shown  in  column  1.  If,  however,  the  heat  is  derived  from  an  incan¬ 
descent  platinum  w'ire,  as  in  column  2,  the  figures  are  different ;  and  white  lead 
is  found  to  absorb  a  less  quantity  of  the  rays  of  heat  when  they  are  luminous, 


and  Indian  ink  more. 

No  1.  No.  i. 

Lampblack  .  .  .  .  ico  .  .  .100 

White  lead  .  .  .  .100  .  .  -56 

Isinglass  .  .  .  .  91  .  .  -54 

Indian  ink  ....  85  ...  95 

Shellac  ....  72  .  .  47 

Metals . 13  .  13*5 


Leslie's  principle  does  apply  to  clothing,  and  it  appears  that  if  we  imitate 
nature,  and,  like  the  Polar  bear,  wear  white,  we  shall  be  warmer  in  winter  and 
cooler  in  summer. 

In  running  streams,  and  even  in  the  Rhine,  what  is  called  “ground  ice”  is 
frequently  found.  This  is  no  contradiction  of  the  laws  already  explained 
with  reference  to  the  cooling  of  water.  The  ice  is  formed  at  the  bottom  of  the 
stream,  because  the  stones  and  other  earthy  matters  forming  the  bed  of  the 
river  emit  or  radiate  heat  when  the  sky  is  very  clear ;  and  as  the  water  of  the 
stream  is  mixed  by  the  current,  and  the  temperature  of  the  bed  of  the  river  is 
lowered  by  radiation,  the  ice  forms  in  spongy  masses,  which  may  rise  to  the 
surface,  carrying  stones  and  even  the  anchors  of  ships  with  them.  The  rays 
of  heat  are  more  readily  absorbed  when  they  fall  upon  bodies  at  angles  near 
the  perpendicular  ;  hence  the  rays  of  the  sun  are  hotter  in  summer  than  in 
winter,  when  they  are  more  oblique. 

If  the  bulb  of  an  air-thermometer  be  brought  near  a  burning  hydrogen 
flame,  its  radiating  power  is  found  to  be  very  low,  although,  as  is  well  known, 
the  heat  of  the  flame  is  so  great  that  it  will  quickly  ignite  a  spiral  of  platinum 
wire  ;  when  the  heat  waves  are  set  in  motion,  emission  or  radiation  takes 
place,  which  will  promptly  affect  the  thermometer.  Tyndall  has  investigated 
the  radiating  and  absorbing  powers  of  gases  and  vapours,  and,  although  they 
are  feeble,  he  has  been  able  to  discover  that  vapours  and  compound  gases 
have  a  much  greater  absorbing  and  emitting  power  than  any  simple  or 
elementary  gas,  such  as  oxygen  or  nitrogen,  or  when  they  are  mechanically 
mixed,  as  in  atmospheric  air.  Had  our  globe  been  surrounded  with  a  gas 
like  olefiant  gas,  the  absorbent  powder  would  have  been  240  times  greater  than 
that  of  oxygen.  Amongst  gases,  those  which  absorb  heat  the  most  also 
radiate  it  freely. 

As  might  be  expected  from  the  analogy  between  light  and  heat-waves,  the 
latter  may  be  reflected,  refracted,  may  undergo  double  refraction,  interference, 
diffraction,  be  absorbed,  and  even  polarized  ;  the  latter  fact  being  proved  by 
the  use  of  tourmaline  plates  or  bundles  of  plates  of  mica. 


16—2 


228 


HEAT. 


TRANSMISSION  OF  HEAT. 


Melloni’s  name  will  ever  be  associated  with  all  the  more  important  experi¬ 
ments  in  which  the  course  of  heat-waves  is  traced  through  various  media. 
As  with  light  there  are  bodies  called  transparent,  diaphanous,  translucent  or 
transparent,  opalescent,  and  opaque,  so  with  reference  to  the  power  of  trans¬ 
mitting  heat,  bodies  generally  are  divided  into  two  classes: 

I. — Diathermanous  or  diathermic  bodies  (81  a,  through,  and  deppo s,  heat), 
permitting  heat-waves  to  travel  through  their  substance.  Examples — 
rock  salt  and  certain  elementary  gases. 

II.— Athermanous  or  adiathermic  bodies,  which  arrest  or  stop  the  progress  of 
the  heat-undulations.  Examples — all  liquids  in  variable  proportions  ; 
alum  in  crystal  and  solution. 

Mr.  B.  Stewart  has  shown  that  bodies  of  the  first  class  are  bad  radiators  of 
heat,  but  that  those  of  the  second  or  adiathermic  class  are  food  radiators. 

It  does  not  follow,  because  substances  like  the  diamond,  glass,  ice,  &c., 
ermit  light-rays  to  pass  through  them,  that  they  will  also  allow  the  heat- 
rays  to  travel  through  in  the  same  proportion.  Glass  perm  ts  the  light  to 
pass  freely  through  its  substance,  but  stops  a  considerable  number  of  the 
heat-undulations  ;  and  alum,  nearly  all.  Rock  salt  is  the  only  substance  which 
is  entitled  to  be  placed  in  the  first  or  true  diathermanous  class,  and  although 
it  does,  according  to  Krupland  and  Stewart,  absorb  certain  of  the  heat-rays 
more  than  others,  still  at  present  it  stands  first,  and  is  therefore  used  in  the 
form  of  plates,  prisms,  and  lenses  for  these  delicate  experiments.  Melloni 
found  that  certain  solids,  cut  into  plates  one-tenth  of  an  inch  in  thickness, 
allowed  the  following  percentage  of  heat  waves  from  an  Argand  lamp  to 
pass  : 


Rock  salt  .... 
Plate  glass  and  Iceland  spar. 
Smoky  quartz  .... 
Transparent  carbonate  of  lead 
Selenite  ..... 
Alum  ..... 
Sulphate  of  copper. 


92,  transparent 

62,  ,, 

57,  nearly  opaque 
52,  transparent 
20,  „ 

12, 

o,  deep  blue 


With  liquids,  when  the  source  of  heat  was  an  Argand  oil  lamp,  and  the 
fluids  enclosed  in  a  glass  cell,  the  results  given  in  Table  I.  were  obtained. 
Table  II.  shows  the  results  obtained  by  Tyndall  from  liquids  enclosed  in  a 
rock-salt  box,  the  source  of  heat  being  an  ignited  platinum  wire  : 


Bisulphide  of  carbon 

Table  1. 
63 

Table  11. 

83 

transparent 

Olive  oil 

3° 

Chloride  of  sulphur  . 

63 

— 

red 

Ether  .... 

.  21 

41 

5) 

Sulphuric  acid  . 

1 7 

41 

V 

Alcohol  .... 

15 

3° 

59 

Solution  of  alum  or  sugar  . 

12 

30 

99 

Water  (distilled) 

.  1 1 

30 

Water  saturated  with  salt  . 

.  — 

26 

Rock  salt  stands  in  the  same  relation  to  heat,  so  far  as  transparency  to 


TRANSMISSION  OF  HEAT. 


229 


FlG.  186. — Mellon! s  Apparatus. 

Argand  oil  l  imp  without  a  glass ;  spirit-l  imp  and  platinum  wire  ;  the  topper  box,  blackened,  to  con¬ 
tain  water  at  212°  F. ;  stand,  to  place  the  oh)ec's  upon,  screen,  with  aptrtures  of  \anous  sizes;  the 
thermo-multiplier  current,  with  the  galvanometer  needle. 

heat-rays  is  concerned,  as  colourless  glass  does  to  the  light-rays.  When  a 
hot  metallic  ball  is  placed  between  the  bulbs  of  a  differential  thermometer, 
the  liquid  remains  stationary,  because  both  are  equally  heated  ;  if,  however, 
a  plate  of  rock  salt  is  interposed  as  a  screen  on  one  side  of  the  ball,  and  a 
plate  of  glass  on  the  other,  the  thermometer  is  immediately  affected,  as  more 
rays  pass  through  the  rock  salt  than  through  the  glass. 

Melloni’s  apparatus  for  these  investigations  may  be  regarded  as  the  model  of 
perfection.  It  includes  the  various  sources  of  heat,  such  as  a  naked  flame,  an 
ignited  platinum  wire,  a  blackened  copper  vessel  containing  water  at  ioov  C. 
(212°  F.),  or  a  copper  plate  heated  to  400°  C.  (752°  F.),  and  is  plainly  shown 
in  Fig.  186. 

The  delicacy  of  the  thermo-multiplier  as  an  indicator  or  measurer  of 
heat  is  most  remarkable,  and  it  will  be  fully  explained  in  another  part  of  this 
work.  The  minute  electrical  currents  set  up  in  the  thermo-multiplier  are 
recorded  by  the  galvanometer  needle. 

It  has  already  been  shown  that  in  bodies  which  arrest  partially  or  wholly 
the  heat-waves,  the  nature  of  the  heat,  or  rather  the  particular  source  from 
which  it  is  obtained,  has  a  great  influence  upon  the  result.  1  hus  fluor-spar 
permits  33  per  cent,  of  the  heat-waves  derived  from  boiling  water  to  pass 
through  its  substance,  whilst  the  power  rises  to  78  per  cent,  when  the  source 
of  heat  is  a  burning  lamp.  Heat-waves  which  have  passed  through  one  plate 
of  glass  will  also  pierce  another,  with  a  small  amount  of  loss  ;  the  same  waves 
are  nearly  all  stopped  by  alum. 

Tyndall’s  discovery,  that  the  vapour  of  water  absorbs  thiiteen  times  more 


230 


HEAT. 


obscure  heat  than  air,  is  a  most  important  fact,  and  shows  why  the  air  con¬ 
taining  vapour  nearer  the  earth  is  warmer  than  that  which  is  dry  and  found 
on  the  summit  of  lofty  mountains.  The  dry  air  allows  the  obscure  heat¬ 
waves  to  travel  through,  and  is  too  diathermanous,  whilst  air  charged  with 
moisture  has  considerable  athermaneity  for  obscure  rays,  which  are  produced 
when  the  rays  of  the  sun  have  passed  through  our  atmosphere  and  fallen  upon 
the  earth  When  the  rays  of  the  sun  fall  upon  the  earth  to  warm  it,  they  are 
radiated  and  then  diffused  ;  a  change  in  their  quality  takes  place,  and  they 
become  obscure  rays  of  heat.  It  is  these  obscure  rays  which  melt  snow,  and 
'  perform  oilier  useful  offices.  It  is  one  of  Kirchoff’s  fundamental  propositions 
i“  that  the  hotter  a  body  is,  the  more  it  gives  of  the  lower  radiations  in  addition 
to  new  and  higher  radiations.” 

The  Conversion  of  Light  Rays  into  Heat  Rays,  and  vice  versa, 
p.y  Change  of  Refrangibility. 

At  the  meeting  of  the  British  Association,  held  at  Newcastle,  in  1863,  Dr. 
Akin  proposed  three  experiments  for  the  conversion  of  rays  of  light  into  heat- 
rays  ;  of  these  one  is  deserving  of  notice,  viz.,  the  proposal  to  collect  the  rays 
of  the  sun  in  a  concave  mirror,  and  then  to  cut  off  the  light  with  “  proper 
absorbents,”  and  to  bring  platinum  foil  into  the  focus  of  invisible  rays. 

Although  Dr.  Akin  was  the  first  to  propose  definitively  to  change  the  refran¬ 
gibility  of  the  ultra-red  rays  of  the  spectrum  by  causing  them  to  raise  platinum 
foil  to  incandescence,  yet  the  chief  merit,  in  connection  with  this  branch  of 
heat,  is  due  to  Dr.  Tyndall,  because,  in  the  spirit  of  Lord  Bacon,  he  was  not 
content  with  a  theory  which  merely  suggested  that  a  certain  result  might  be 
obtained,  but  industriously  worked  out  the  crude  idea,  and  proved  that  it  was 
substantially  true,  by  devising  a  number  of  clever  and  original  experiments, 
which  had  never  been  shown  before. 

In  the  article  on  Light  (p.  92),  the  change  of  refrangibility  of  certain  rays  at 
the  violet  end  of  the  spectrum,  and  the  beautiful  experiments  with  “fluorescence,” 
by  Professor  Stokes,  have  already  been  specially  considered.  And  just  as  he 
obtained  a  large  proportion  of  these  rrys,  existing  in  and  beyond  the  violet, 
by  using  prisms  of  quartz,  so  Melloni,  by  using  a  prism  of  rock-salt,  was  en¬ 
abled  to  prove  that  the  ultra-red  rays  discovered  by  Sir  W.  Herschel  formed 
an  invisible  heat  spectrum  as  long  as  the  visible  one.  Other  experimentalists 
continued  the  investigation,  especially  Professor  Muller,  of  Freiberg,  who 
worked  out  a  curve  expressing  the  heating  power  of  the  whole  spectrum  ;  but 
it  was  left  for  Tyndall  to  complete  the  investigation,  and  directly  isolate  the 
invisible  or  obscure  rays  of  heat ;  and  as  Stokes,  by  lowering  the  refrangibility 
of  the  invisible  ultra-violet  rays,  rendered  them  visible,  so  Tyndall,  by  raising 
the  refrangibility  of  the  ultra-red  rays,  rendered  them  also  visible.  The  instru¬ 
ments  he  used,  to  quote  his  own  words,*  “  consisted  of  the  electric  lamp  of 
Duboscq  and  the  linear  thermo-electric  pile  of  Melloni. 

“  The  spectrum  was  formed  by  means  of  lenses  and  prisms  of  rock-salt;  it 
was  equal  in  width  to  the  length  of  the  row  of  elements  forming  the  pile;  and 
the  latter  being  caused  to  pass  through  its  various  colours  in  succession,  and 
also  to  search  the  space  right  and  left  of  the  visible  spectrum,  the  heat  falling 
upon  it  at  every  portion  of  its  march  was  determined  by  the  deflection  of  an 
extremely  sensitive  galvanometer. 


*  “Proceedings  of  the  Rnval  Institution  of  Great  Britain,  ’  vol.  iv.,  part J.  Trofessor  Tyndall,  “On 
Combustion  by  Invisible  Bays.” 


INVISIBLE  HEAT  RAYS. 


231 


Fig.  187. —  Dr.  Tyndalls  Diagram. 


“  As  in  the  case  of  the  solar  spectrum,  the  heat  was  found  to  augment  from 
the  violet  to  the  red,  while  in  the  dark  space  beyond  the  red  it  rose  to  a  maxi¬ 
mum.  The  position  of  the  maximum  was  about  as  distant  from  the  extreme 
red  in  the  one  direction  as  the  green  of  the  spectrum  in  the  opposite  one. 

“The  augmentation  of  temperature  beyond  the  red  in  the  spectrum  of  the 
electric  light  is  sudden  and  enormous.  Representing  the  thermal  intensities 
by  lines  of  proportional  lengths,  and  erecting  these  lines  as  perpendiculars 
at  the  places  to  which  they  correspond,  when  we  pass  beyond  the  red  these 
perpendiculars  suddenly  and  greatly  increase  in  length,  reacli  a  maximum, 
and  then  fall  somewhat  more  suddenly  on  the  opposite  side  of  the  maximum. 
When  the  ends  of  the  perpendiculars  are  united,  the  curve  beyond  the  red, 
representing  the  obscure  radiation,  rises  in  a  steep  and  massive  peak,  which 
quite  dwarfs  by  its  magnitude  the  radiation  of  the  luminous  portion  of  the 
spectrum.  * 

“Interposing  suitable  substances  in  the  path  of  the  beam,  this  peak  may 
be  in  part  cut  away.  Water,  in  certain  thicknesses,  does  this  very  effectually. 

“  The  vapour  of  water  would  do  the  same;  and  this  fact  enables  us  to  account 
for  the  difference  between  the  distribution  of  heat  in  the  solar  and  in  the 
electric  spectrum.  The  comparative  height  and  steepness  of  the  ultra-red 
peak  in  the  case  of  the  electric  light  are  much  greater  than  in  the  case  of  the 
sun,  as  shown  by  the  diagram  of  Professor  Muller.  No  doubt  the  reason  is, 
that  the  eminence  corresponding  to  the  position  of  maximum  heat  in  the  solar 
spectrum  has  been  cut  down  by  the  aqueous  vapour  of  our  atmosphere. 
Could  a  solar  spectrum  be  produced  beyond  the  limits  of  the  atmosphere,  it 
would  probably  show  as  steep  a  mountain  of  invisible  rays  as  that  exhibited 
by  the  electric  light,  which  is  practically  uninfluenced  by  atmospheric  absorp¬ 
tion. 

“  Having  thus  demonstrated  that  a  powerful  flux  of  dark  rays  accompanies 
the  bright  ones  of  the  electric  light,  the  question  arises,  ‘  Can  we  not  detach 
the  former,  and  experiment  on  them  alone?' 

“  In  the  author’s  first  experiments  on  the  invisible  radiation  of  the  electric 
light,  black  glass  w  as  the  substance  made  use  of.  I  he  specimens,  howe\er, 


23  2 


HEAT. 


which  he  was  able  to  obtain  destroyed,  along  with  the  visible,  a  considerable 
portion  of  the  invisible  radiation.*  But  the  discovery  of  the  deportment  of 
elementary  gases  directed  his  attention  to  other  simple  substances.  He  exa¬ 
mined  sulphur  dissolved  in  bisulphide  of  carbon,  and  found  it  almost  perfectly 
transparent  to  the  invisible  rays.  He  also  examined  the  element  bromine,  and 
found  that,  notwithstanding  its  dark  colour,  it  was  eminently  transparent  to 
the  ultra-red  rays.  Layers  of  this  substance,  for  example,  which  entirely  cut 
off  all  the  light  of  a  brilliant  gas-flame,  transmitted  its  invisible  radiant  heat 
with  freedom.  Finally,  he  tried  a  solution  of  iodine  in  bisulphide  of  carbon, 
and  arrived  at  the  extraordinary  result,  that  a  quantity  of  dissolved  iodine 
sufficiently  opaque  to  cut  off  the  light  of  the  mid-day  sun  was,  wfithin  the 
limits  of  experiment,  absolutely  transparent  to  invisible  radiant  heat. 

“  This,  then,  is  the  substance  by  which  the  invisible  rays  of  the  electric 
light  may  be  almost  perfectly  detached  from  the  visible  ones.  Concentrating 
by  a  small  glass  mirror,  silvered  in  front,  the  rays  emitted  by  the  carbon  points 
of  the  electric  lamp,  we  obtain  a  convergent  cone  of  light.  Interposing  in  the 
path  of  this  concentrated  beam  a  cell  containing  the  opaque  solution  of  iodine, 
the  light  of  the  cone  is  utterly  destroyed,  while  its  invisible  rays  are  scarcely, 
if  at  all,  meddled  with.  These  converge  to  a  focus,  at  which,  though  nothing 
can  be  seen  even  in  the  darkest  room,  the  following  series  of  effects  may  be 
produced : 

“  When  a  piece  of  black  paper  is  placed  in  the  focus,  it  is  pierced  by  the 
invisible  rays,  as  if  a  white-hot  spear  had  been  suddenly  driven  through  it. 
The  paper  instantly  blazes,  without  apparent  contact  with  anything  hot. 

“  A  piece  of  brown  paper  placed  at  the  focus  soon  shows  a  red-hot  burning 
surface,  extending  over  a  considerable  space  of  the  paper,  which  finally  bursts 
into  flame. 

“  The  wood  of  a  hat-box  similarly  placed  is  rapidly  burnt  through.  A  pile 
of  wood  and  shavings,  on  which  the  focus  falls,  is  quickly  ignited,  and  thus  a 
fire  may  be  set  burning  by  the  invisible  rays. 

“  A  cigar  or  a  pipe  is  immediately  lighted  when  placed  at  the  focus  of  invi¬ 
sible  rays. 

“  Discs  of  charred  paper  placed  at  the  focus  are  raised  to  brilliant  incan¬ 
descence  ;  charcoal  is  also  ignited  there. 

“  A  piece  of  charcoal,  suspended  in  a  glass  receiver  full  of  oxygen,  is  set  on 
fire  at  the  focus,  burning  with  the  splendour  exhibited  by  this  substance  in  an 
atmosphere  of  oxygen.  The  invisible  rays,  though  they  have  passed  through 
the  receiver,  still  retain  sufficient  power  to  render  the  charcoal  within  it  red  hot 

“  A  mixture  of  oxygen  and  hydrogen  is  exploded  in  the  dark  focus,  through 
the  ignition  of  its  envelope. 

“A  strip  of  blackened  zinc-foil  placed  at  the  focus  is  pierced  and  inflamed 
by  the  invisible  rays.  By  gradually  drawing  the  strip  through  the  focus,  it 
may  be  kept  blazing  with  its  characteristic  purple  light  for  a  considerable  time. 
This  experiment  is  particularly  beautiful. 

“  Magnesium  wire,  presented  suitably  to  the  focus,  burns  with  almost  into¬ 
lerable  brilliancy. 

“  The  effects  thus  far  described  are,  in  part,  due  to  chemical  action.  The 
substances  placed  at  the  dark  focus  are  oxidizable  ones,  which,  when  heated 
sufficiently,  are  attacked  by  the  atmospheric  oxygen,  ordinary  combustion 


*  “Th"  glass  in  thin  layers  had  a  greenish  hue:  I  ha\e  since  found  black  glass  far  mere  diathermic.*’ 


INVISIBLE  HEAT  RAYS. 


233 


being  the  results.  But  the  experiments  maybe  freed  from  this  impurity.  A  thin 
plate  of  charcoal,  placed  in  vacuo ,  is  raised  to  incandescence  at  the  focus  of 
invisible  rays.  Chemical  action  is  here  entirely  excluded.  A  thin  plate  of 
silver  or  copper,  with  its  surface  slightly  tarnished  by  the  sulphide  of  the  metal, 
so  as  to  diminish  its  reflective  power,  is  raised  to  incandescence  either  in  vacuo 
or  in  air.  With  sufficient  battery-power  and  proper  concentration,  a  plate  of 
platinized  platinum  is  rendered  white  hot  at  the  focus  of  invisible  rays;  and 
when  the  incandescent  platinum  is  looked  at  through  a  prism,  its  light  yields 
a  complete  and  brilliant  spectrum.  In  all  these  cases  we  have,  in  the  first 


Fig.  188. —  Tyndalls  Apparatus  for  showing  the  heating-power  of  the 

Invisible  Rays. 

A,  the  lantern  containing  the  electric  lamp  and  silvered  mirror ;  b,  the  plate-g.ass  trough,  having  an 
outer  jacket,  through  which  cold  water  circulates,  to  prevent  the  solution  of  iodine  in  bisulphide  ot 
carbon  boiling ;  c,  the  cistern  of  water  and  pipe  passing  to  jacket,  r>,  and  (lowing  away  to  d,  e,  s  an 

to  cairy  zmcfoil. 


place,  a  perfectly  invisible  image  of  the  coal-points  formed  by  the  mirror;  and 
no  experiment  hitherto  made  illustrates  the  identity  of  light  and  heat  more 
forcibly  than  this  one.  When  the  plate  of  metal  or  of  charcoal  is  placed  at 
the  focus,  the  invisible  image  raises  it  to  incandescence,  and  thus  prints  itself 
visibly  upon  the  plate.  On  drawing  the  coal-points  apart,  or  on  causing  them 
to  approach  each  other,  the  thermograph  of  the  points  follows  theii  motion. 
By  cutting  the  plate  of  carbon  along  the  boundary  of  the  thermograph,  ve 
might  obtain  a  second  pair  of  coal-points,  of  the  same  shape  as  the  original 
ones,  but  turned  upside  down  ;  and  thus  by  the  rays  of  one  pair  ot  coal-points, 


234 


HEAT. 


which  are  incompetent  to  excite  vision,  we  may  cause  a  second  pair  to  emit 
all  the  rays  of  the  spectrum. 

“  The  ultra-red  radiation  of  the  electric  light  is  known  to  consist  of  ethereal 
undulations  of  greater  length,  and  slower  periods  of  recurrence,  than  those 
which  excite  vision.  When,  therefore,  those  long  waves  impinge  upon  a  plate 
of  platinum,  and  raise  it  to  incandescence,  their  period  of  vibration  is  changed. 
The  waves  emitted  by  the  platinum  are  shorter  and  of  more  rapid  recurrence 
than  those  falling  upon  it;  the  refrangibility  being  thereby  raised,  and  the 
invisible  rays  rendered  visible.” 


ELECTRICITY, 

FRICTIONAL  OR  STATICAL. 

'T'HERE  is  no  branch  of  science  more  fascinating  to  the  youthful  mind  than 
this  most  curious  form  or  mode  of  motion. 

By  motion  it  is  evoked.  There  is  nothing  more  to  do  than  to  rub  some 
body,  such  as  glass  or  sealing-wax,  with  silk  or  flannel,  or  to  lay  a  warm 
sheet  of  brown  paper  on  a  tea-tray,  and  rub  it  well  with  india  rubber ;  and  the 
electric  force  becomes  apparent,  either  by  cieating  motion  again,  causing 
light  substances,  such  as  feathers  or  the  down  of  feathers,  to  move  towards 
the  surface  on  which  the  force  has  been  set  free,  or  if  observed  in  a  darkened 
room,  the  sheet  of  brown  paper  is  found  to  give  light,  a  crackling  sound  is 
heard,  and  small  sparks  are  visible  as  the  sheet  of  paper  is  drawn  up  from 
the  tea-tray. 

This  can  be  done  over  and  over  again.  It  is  only  necessary  to  dry  the 
paper  by  holding  it  before  the  fire,  and  the  same  attractive  power,  the  same 
curious  fire,  is  apparent.  The  sheet  of  paper  itself,  after  being  well  rubbed, 
will  move  towards  the  body  of  the  person  who  holds  it  up  by  one  corner,  and 
is  said  to  be  attracted  because  it  is  electrified  or  electrized. 

One  of  the  “seven  wise  men  of  Greece,”  named  1  hales,  from  whose  school 
at  Miletus,  in  Ionia,  came  Socrates  and  his  disciples,  has  always  been  con¬ 
sidered  as  the  first  who  introduced  a  scientific  method  of  philosophising 
among  the  Greeks,  600  years  before  the  Christian  era. 

To  this  philosopher  is  ascribed  the  following  : 

“  That  God  is  the  most  ancient  being,  who  has  neither  beginning  nor  end  ; 
that  all  things  are  full  of  God  ;  and  that  the  world  is  the  beautiful  work  ot 
God.” 

A  principle  of  motion,  wherever  it  exists,  is,  according  to  Thales,  mtna. 


ELECTRICITY. 


236 


Hence  be  taught  that  the  magnet  and  amber  ( rjXtKTpov )  are  endued  with  a 
soul,  which  is  the  cause  of  their  attracting  powers.*  It  is  from  the  Greek 
name  of  amber,  a  fossil  resin,  that  the  science  derives  its  name— “  Elec¬ 
tricity.” 

There  are  many  substances  which  are  electrized  by  friction — gutta-percha, 
the  skin  of  a  cat,  sulphur,  the  different  resins,  and  especially  shellac,  the 
chief  constituent  of  good  sealing-wax,  glass,  and  the  greater  number  of 
crystals,  &c.  On  the  other  hand,  there  are  many  bodies,  such  as  the  metals, 
in  which,  apparently,  the  power  cannot  be  developed. 

The  earlier  experimentalists  divided  all  bodies  into  electrics  and  non-electrics: 
the  former  they  considered  could  be  electrized  by  friction;  the  latter,  apparently, 
not  so.  It  was  then  discovered  that  this  classification  was  not  a  correct  one, 
and  that  the  reason  the  so-called  non-electrics  did  not  show  any  electrical 
energy  when  rubbed  was  because  of  their  “  conductivity ;  ”  as  fast  as  the 
electricity  was  produced,  it  was  conducted  away  to  the  earth  and  lost.  Finally, 
they  discovered,  by  cutting  off  the  conducting  communication  with  the  earth 
by  attaching  the  so-called  non-electrics,  such  as  a  rod  of  metal  to  one  of 
glass  and  then  rubbing  it,  that  now  the  metal  could  attract  light  particles 
— down,  pith  of  the  elder,  gold  leaf,  &c.— and  was  then  said  to  be  “  insulated.” 
An  instrument  had  now  to  be  invented  to  indicate  the  disturbance  of  electrical 
equilibrium  -  this  instrument  was  appropriately  called  an  “  electroscope,”  or 
instrument  for  showing  electrical  excitation.  Commencing  with  the  more 
simple  forms,  we  may  trace  them  up  to  the  most  refined  and  delicate  instru¬ 
ments. 


Fig.  189. — A  simple  form  of  Electroscope. 

a,  the  needle  and  coik;  b,  the  cup  attached  to  the  featner. 


I.  The  mouth  of  a  clean,  dry,  empty  wine-bottle  is  closed  with  a  cork, 
through  which  a  short  needle  has  been  passed,  the  point  being  up- 


*  “  Enfield’s  History  of  Philosophy,”  p.  82. 


ELECTRICITY. 


237 


wards.  On  this  point  is  balanced  an  eagle’s  feather,  to  whicn  a  little 
cup  made  of  glass,  or  any  other  convenient  hard  substance,  has  been 
fixed.  The  glass  cup,  or  cap,  with  the  feather  attached,  resting  on  the 
point  of  the  needle,  offers  little  or  no  resistance  or  friction,  and  hence 
the  feather  moves  freely  like  a  suspended  magnet  in  any  direction. 

When  a  stick  of  sealing-wax  is  rubbed  and  advanced  towards  the 
feather,  the  latter  is  immediately  attracted,  and  will  follow  the  sealing* 
wax  round  with  great  rapidity. 

After  the  feather  has  been  touched  several  times  by  the  electrized 
wax,  it  is  now  found,  on  approaching  the  electrified  sealing-wax,  that  the 
feather  is  repelled — not  so  energetically  as  it  was  attracted,  but  quite 
sufficiently  so  as  to  be  distinctly  apparent. 

“  Attraction  ”  and  “  repulsion  ”  are  thus  illustrated  : 

II.  A  glass  tube  or  rod  is  bent 'at  right  angles,  and  the  end  fixed  to  some 
convenient  support,  viz.,  a  round  or  square  piece  of  wood.  A  pith- 
ball  suspended  from  it  by  a  silk  filament  becomes  a  sensitive  and 
simple  electroscope  or  electric  pendulum. 


Fig.  190. — An  Electroscope. 

A  A,  the  plass  support;  b,  the  pith-ball  suspended;  c,  the  e  ectrized  glass. 

If  two  balls  are  suspended  side  by  side,  and  the  electrified  wax  or 
glass  brought  towards  them,  they  are  found,  after  being  attracted  to 
and  touching  the  electrized  glass,  to  repel  each  other. 

“Attraction”  and  “repulsion”  are  again  demonstrated: 

Another  modification  of  the  above  may  be  arranged  bv  making  two 
similar  supports,  like  that  in  Fig.  190,  and  suspending  a  pith-ball  from 
each.  If  the  two  balls  placed  close  together  are  electrized,  they  repel 
each  other;  but  if  the  two  stands  are  moved  a  little  way  from  each  other. 


238 


ELECTRICITY. 


and  one  electrized  with  the  rubbed  glass  and  the  other  with  the  rubbed 
wax.  the  two  balls  attract  each  other. 


Fig.  191. — The  two  Stands  and  Titli-balls. 

g  is  electrified  with  the  rubbed  glass;  w,  with  the  rubbed  wax. 


N.B. — A  little  tinfoil  neatly  pasted  round  the  joints  where  the  threads 
are  suspended  assists  the  accumulation  of  electricity ;  and  if  the  pith- 
balls  are  gilt  and  suspended  by  very  fine  hair-like  wires  of  silver  or 
gold,  the  effects  are  more  decided — the  pith-balls  do  not  cling  together. 

In  this  experiment  it  would  appear  that  the  electricity  from  glass 
attracts  that  from  the  wax;  whilst  separately  (Fig.  190)  they  are  mutu¬ 
ally  repulsive  of  their  own  particles,  and  hence  one  electricity  was 
called  vitreous  and  the  other  resinous. 

III.  A  very  delicate  electroscope  is  that  in  whicn  the  material  to  be  moved 
by  the  electrical  force  is  itself  remarkably  light,  and  must  be  screened 
from  the  air  to  prevent  it  being  agitated  or  blown  off  by  any  current 
of  wind  suddenly  impinging  upon  it.  The  material  is  gold  leaf,  which 
can  now  be  purchased  in  books  cut  ready  for  use.  It  is  usual  to  attach 
two  gold  leaves  to  the  opposite  sides  of  a  thin  plate  of  brass,  or  card 
covered  with  gold  paper;  this  is  held  by  a  pair  of  pincers,  at  the  end  of 
a  brass  rod  passing  through  a  glass  tube  cemented  in  a  brass  cap.  at¬ 
tached  to  a  bell-glass.  By  this  mode  of  suspension  the  brass  wire, 
which  terminates  with  a  circular  brass  plate  or  table,  is  supported 
on  the  glass  tube  (a  bad  conductor  of  electricity),  and  the  tube  and 
cup  are  again  supported  by  the  bell-glass,  so  that  good  insulation  is 
secured.  When  great  refinement  is  required,  it  is  usual  to  place  a 
glass  shade  over  the  whole ;  the  latter  is  perforated  at  the  top  with  a 
hole,  about  one  inch  in  diameter,  through  which  the  brass  rod  and 
table  are  passed,  and  lumps  of  lime  being  placed  in  both  glasses,  the 
air  is  kept  dry,  and,  the  aqueous  vapour  being  absorbed,  there  is  no 
deposit  of  dew-like  moisture  under  either  of  the  glasses.  (Fig.  192.) 

A,  brass  table  or  disc,  with  wire  attached,  and  pincers  P,  to  hold  the 
gilt  card  to  which  the  gold  leaves  are  attached  ;  C,  the  inner  bell-glass, 


ELECTRICITY 


239 


upon  which  the  cap  carrying  the  glass  tube  D,  through  which  the  brass 
rod  passes,  is  cemented;  E  E,  the  outer  glass  shade,  perforated  with  a 
hole  in  the  top,  about  I  in.  in  diameter,  to  allow  the  brass  rod  to  pass 
through.  N.B. — The  table  or  round  plate  unscrews  from  the  wire,  in 
order  to  allow  this  to  be  done:  both  the  inner  bell-glass  and  the  outer 
glass  shade  fit  nicely  into  grooves  made  in  a  square  mahogany  stand, 
G  G,  neatly  fitted  with  a  drawer  to  hold  quicklime.  The  part  of  the 
stand  covered  with  the  two  glasses  is  perforated  with  holes,  in  order 
that  the  desiccating  power  of  the  lime  may  take  full  effect  on  the  air 
enclosed  by  the  two  glasses.  It  is  sometimes  usual  in  this  electroscope, 
called  Bennet’s,  to  place  two  rods  and  balls  in  the  stand;  so  that,  if  the 
gold  leaves  are  too  highly  charged,  they  may  not  be  torn  off,  but,  by 
touching  the  brass  rods,  the  excess  of  electricity,  which  might  damage 


A 


Fig.  192. — A  more  delicate  Electroscope. 


the  instrument,  is  carried  off  to  the  earth.  For  other  reasons,  the  brass 
rods  connected  with  the  earth  exalt  the  power  of  the  electricity  applied, 
however  feeble  it  may  be. 

An  electrized  glass  rod,  brought  towards  the  cap  of  the  instrument, 
causes  the  gold  leaves  to  diverge  or  repel  each  other;  when  left  dnci- 
gent  with  the  electricity  from  glass,  they  instantly  fall  on  the  approach 
of  an  electrized  piece  of  wax.  The  little  table  is  convenient  for  stand¬ 
ing  any  object  on,  or  else  a  plain  ball  would  perhaps  be  a  better  ter¬ 
minal,  as  the  edges  of  the  table,  unless  nicely  rounded,  are  apt  to  dis¬ 
sipate  the  electricity.  .  , 

It  is  not  necessary  to  touch  the  cap  of  the  electroscope  with  the 


240 


ELECTRICITY. 


electrized  bodies,  in  order  to  pass  into  or  on  the  rod  connected  with  the 
gold  leaves  the  electricity  we  wish  to  examine.  By  an  influence  called 
“  induction,”  to  be  more  fully  explained  hereafter,  the  gold  leaves  are 
found  to  possess  the  same  kind  of  electricity  as  that  enjoyed  by  the 
electrized  body. 

Another  electroscope  invented  by  Dr.  Robert  Hare,  of  the  University 
of  Pennsylvania,  in  which  one  gold  leaf  only  is  used,  is  worthy  of  par¬ 
ticular  notice  here,  and  is  described  in  Noad’s  “  Manual  of  Electricity:” 

“  The  leaf,  about  3  in.  long  and  3-ioths  of  an  inch  wide,  is  suspended, 
according  to  Singer’s  method,  in  the  centre  of  a  globular  or  other 
shaped  glass  vessel  from  a  brass  wire  surmounted  with  a  brass  cap.  A 
similar  rod  of  brass,  carrying  at  each  end  a  small  disc  of  brass  or  gilt 
wood,  about  half  an  inch  in  diameter,  passes  through  the  side  of  the 
vessel,  so  that  the  internal  disc  shall  be  immediately  opposite  the  lower 
end  of  the  suspended  leaf.  This  wire  slides  freely  through  a  socket,  so 
that  the  internal  disc  may  be  adjusted  at  any  required  distance  from 
the  leaf. 

“  When  it  is  employed  to  detect  electricity,  the 
lateral  wire  is  uninsulated  by  hanging  a  wire  from 
it  to  the  earth,  and  the  body  to  be  tested  is  brought 
into  contact  with  the  cap.  If  the  distance  between 
the  gold  leaf  and  the  disc  B  is  very  small,  the  most 
minute  force  of  attraction  is  rendered  apparent. 
When  it  is  required  to  determine  the  kind  of  elec¬ 
tricity  with  which  a  body  is  charged,  the  insulated 
disc  B  is  brought  as-  near  as  possible  to  the  leaf, 
and  electrified  either  positively  (with  excited  glass) 
or  negatively  (with  excited  wax) ;  the  gold  leaf  is 
first  attracted,  and  then  repelled.  Under  these 
circumstances  the  body  to  be  tested  is  brought 
into  contact  with  the  cap  or  with  D :  if  its  elec¬ 
tricity  be  of  the  same  nature  as  that  with  which 
the  leaf  is  charged,  the  latter  will  diverge  more 
freely;  if  of  the  contrary  nature,  it  will  collapse 
towards  B. 

“  By  placing  a  gilt  disc  on  each  side  of  the  gold 
leaf,  Mr.  Gassiot  obtained  signs  of  electrical  exci¬ 
tation  from  a  single  cell  of  the  voltaic  battery.” 

From  the  preceding  experiments  the  following  conclusions  may  be  arrived  at: 

I.  That  an  electrified  body  has  the  power  to  attract  another  which  is  not 
electrical. 

II.  That  two  bodies  similarly  electrified  repel  each  other. 

III.  That  the  electricity  derived  from  glass  is  different  from  that  obtained 

from  wax;  and  that,  being  dissimilar,  they  attract  each  other. 

IV.  The  two  electricities  have  names  to  distinguish  them  from  each  other: 

one  is  called  vitreous,  because  obtained  from  glass  ;  and  the  other 
resinous,  because  usually  obtained  from  sealing-wax.  The  whole  is 
summed  up  in  the  two  simple  statements: — Similar  electricities  repel 
each  other;  dissimilar  electricities  attract  each  other. 

V-  The  electricity  a  substance  gives  out  by  friction  is  not  always  the  same, 
but  depends  on  the  nature  of  the  rubber  used,  and  other  circumstances. 


Fig.  193. 

Dr.  Robert  Hare’s  single¬ 
leaf  Electroscope. 


THEORIES  OE  ELECTRICITY. 


241 


Glass,  when  rubbed  with  a  cat’s  skin,  gives  resinous  electricity,  and 
vitreous  if  rubbed  with  silk.  Polish  and  temperature,  as  shown  by  De 
la  Rive,  exercise  a  remarkable  influence.  When  bodies  are  highly 
polished,  they  have  a  greater  tendency  to  give  by  friction  vitreous  elec¬ 
tricity,  or  to  acquire  it;  by  elevating  the  temperature  of  bodies,  they 
have  a  greater  tendency  to  acquire  resinous  electricity. 

A  piece  of  roughened  or  ground  glass,  rubbed  against  a  smooth  and 
highly  polished  piece  of  glass,  becomes  resinous,  whilst  the  smooth 
glass  is  negative. 

VI.  No  single  electricity  can  be  evolved  without  an  equal  excitation  of  the 
other  or  opposite  electrical  force ;  the  rubber  and  the  substance  rubbed 
are  always  in  opposite  states — the  silk  handkerchief  being  resinous,  the 
glass  vitreous. 

Electricity  being,  as  it  were,  a  resident  in  all  substances,  it  is  said  to  be 
quiescent  when  the  two  opposite  forces  have  neutralized  each  other.  It  is  then 
called  the  static  state  of  electricity ;  and  this  state  is  supposed  to  be  the  normal 
condition  of  all  bodies  before  they  become  electrical. 

When  the  two  electricities  travel  towards  each  other,  or  pass  in  sparks 
through  intervals  of  air,  or  move  insensibly  along  a  wire  or  other  conductor, 
it  is  said  to  be  in  a  dynamic  state,  or  condition  of  motion  or  circulation,  which 
becomes  very  evident  in  watching  the  motion  of  an  electrical  machine,  or  the 
single  voltaic  circle  of  zinc  and  copper  placed  in  acid  and  water.  The  dynamic 
state  is  sometimes  spoken  of  as  electric  tension,  and  an  electric  current  as  a 
continuous  dynamic  state. 


THEORIES  OF  ELECTRICITY. 

By  the  theory  of  Du  Fay,  as  altered  by  Symmcr,  it  is  supposed  that  two 
forces,  called  fluids,  exist  in  every  substance,  whatever  may  be  its  nature — 
solid,  liquid,  or  gaseous. 

Each  of  the  two  fluids  is  supposed  to  be  very  subtile  and  rare,  quite  impon¬ 
derable,  and  consisting  of  particles  that  repel  eacli  other. 

When  the  twro  fluids  are  sepaiated,  electrical  effects  are  obtained ;  and  when 
they  unite,  the  electrical  power  ceases,  for  they  have  now  combined  to  form 
neutral  fluid,  or  natural  electricity.  As  before  stated,  one  electricity  is  called 
vitreous,  and  the  other  negative. 

The  repellent  nature  of  the  electrical  particles  is  supposed  to  cause  them 
to  arrange  themselves  on  the  surface  of  conducting  bodies,  where  they  remain, 
because  they  are  checked  in  their  movement  by  the  non  or  badly  conducting 
air  with  which  they  are  surrounded. 

Non  or  bad  conductors  are  supposed  to  retain  the  fluids,  and  to  interfere 
with  their  movements. 

This  theory  of  Symmer  is  a  most  convenient  and  simple  one  for  the  young 
student,  and  will  help  him  to  fix  the  main  experimental  truths  of  electricity  in 

his  mind.  _  . , 

The  second  theory,  devised  by  Benjamin  franklin,  supposes  that  one  fluid 
only  exists,  the  particles  of  which  mutually  repel  each  other.  I  he  electrical 
fluid  is  supposed  to  be  combined  with  all  matter:  matter  without  electricity  is 
supposed  to  be  repulsive  of  its  own  particles.  When  a  body  is  in  a  quiescent 


242 


ELECTRICITY. 


electrical  state,  then  the  matter  is  exactly  saturated  with  electricity,  and  it  is 
in  a  natural  condition. 

If  the  substance  is  rubbed,  it  either  gains  or  loses  the  electrical  fluid.  The 
acquisition  of  more  electricity  is  said  to  confer  a  plus  or  positive  state  of  elec¬ 
tricity  :  the  loss  of  the  electricity  places  the  substance  in  a  minority  with 
regard  to  electricity;  it  is  now  said  to  be  indued  with  minus  or  negative 
electricity. 

What  Symmer  terms  vitreous  electricity  Franklin  calls  positive  electricity; 
what  Symmer  styles  resinous  electricity  is  called  by  Franklin  negative  electri¬ 
city. 

it  is  of  little  consequence  which  theory  we  adopt,  for  one  or  the  other  must 
be  wrong;  most  likely,  both  are  untrue.  We  have  seen  that  a  certain  vibra¬ 
tion  of  particles  will  produce  invisible  heat  rays,  and,  when  they  are  quickened 
in  their  pulsation,  light  rays  ;  as  in  Tyndall’s  experiments,  the  concentrated 
invisible  rays  of  heat,  falling  on  a  piece  of  platinum-foil,  are  converted  into 
visible  or  light  rays.  The  same  wave  theory  will  doubtless  be  ultimately  applied 
to  electricity,  which  may  only  be  some  remarkable  vibratory  state  of  the  ether 
pervading  all  matter  and  space.  And  this  opinion  was  held,  forty  years  before 
Galvani,  by  Sultzer,  who  first  experimented  with  pieces  of  silver  and  lead.  By 
placing  them  jon  opposite  sides  of  the  tongue,  and  then  bringing  the  two  in 
contact,  he  noticed  a  peculiar  metallic  taste,  like  vitriol. 

Here  again  it  will  be  understood  why  so  much  space  was  devoted  to  the 
consideration  of  the  “universal  ether,”  at  the  commencement  of  the  article 
on  Light. 


EXPERIMENTS  WITH  THE  ELECTROSCOPE. 

An  electroscope  is  easily  made  with  a  wide,  clean  lamp-glass.  A  cork  is 
fitted  into  it,  and  through  the  cork  is  passed  a  wire,  one  end  of  which  is  beaten 
out,  so  as  to  give  a  sufficiently  large  and  flat  surface;  a  pair  of  small  gold 
leaves  are  attached  to  this  end  of  the  wire,  and  to  the  other  is  fixed  a  round 
piece  of  cardboard,  covered  with  tinfoil  or  gold  paper.  When  the  wire  is 
passed  through  the  cork,  the  gold  leaves  may  be  attached  by  moistening  the 
flattened  end  of  the  wire  with  a  little  gum,  and  bringing  it  carefully  down 
upon  the  cut  gold  leaves  in  the  book.  The  second  gold  leaf  is  the  most  diffi¬ 
cult  to  get  on.  When  both  leaves  are  in  their  places,  the  cork,  wire,  and  leaves 
may  be  placed  in  the  lamp-glass,  and  the  cardboard  table  fixed  on  the  wire. 

I.  A  little  coffee,  quickly  ground  in  a  mill,  received  in  a  warm  dry  beaker 
glass,  and  then  sprinkled  upon  the  table  or  plate  of  the  electroscope, 
causes  the  leaves  to  diverge. 

IT.  Some  whiting  or  cha'k,  dried  and  put  into  the  valve  of  a  pair  of  bellows, 
and  then  forced  o.  t  upon  the  electroscope  with  the  wind,  very  soon 
causes  the  leaves  to  be  deflected. 

III.  A  large  lump  of  sugar  held  over  the  electroscope,  and  sawed  in  various 

places  with  a  saw,  affects  the  instrument  as  the  sugar-dust  falls  upon  it. 

IV.  After  playing  a  tune  on  a  violin  with  a  dry  and  well  rosined  bow,  if 

the  latter  is  passed  lightly  over  the  electroscope,  electrical  excitation 
is  apparent. 

V.  A  roll  of  dry  warm  flannel  rubbed  against  a  stick  of  sealing-wax 


EXPERIMENTS  WITH  THE  ELECTROSCOPE.  243 


causes  the  leaves  of  the  electroscope  to  stand  out,  and  repel  each 
other;  but  they  hill  directly  the  sealing-wax  is  applied,  because  the 
two  electrical  and  opposite  forces — vitreous  from  the  flannel  and 
resinous  from  the  wax — neutralize  each  other,  the  rubber  and  the 
substance  rubbed  giving  always  the  opposite  states. 

VI.  While  the  leaves  are  divergent  with  the  rubbed  wax,  bring  an  excited 
glass  rod  or  tube  towards  the  electroscope,  as  before ;  the  leaves 
fall  immediately. 

VII.  Mr.  Symmer,  whose  name  has  already  been  mentioned  in  connection 
with  one  of  the  theories  of  electricity,  tried  some  very  amusing  ex¬ 
periments  with  silk  stockings.  lie  put  upon  the  same  leg  a  worsted 
stocking,  and  over  that  a  silk  one,  and  rubbing  the  outer  stocking 
before  a  fire,  he  slipped  the  silk  one  suddenly  off,  and,  the  sides  re¬ 
pelling  each  other,  the  stocking  appeared  to  be  inflated,  and  to  retain 
the  same  shape  as  if  the  leg  were  in  it ;  and  of  course,  if  the  silk 
stocking  had  been  carefully  approached  towards  the  electroscope, 
the  leaves  would  have  been  rendered  powerfully  divergent. 

VIII.  A  crystal  of  Iceland  spar  cemented  to  an  insulating  glass  rod,  then 
pressed  in  the  hand,  and  placed  immediately  on  a  very  delicate  elec¬ 
troscope,  will  cause  a  slight  divergence. 

IX.  A  disc  of  insulated  cork,  gently  warmed  and  simply  pressed  against 
another  one  of  the  same  material,  will  show  a  certain  minute  amount 
of  electrical  energy  when  applied  to  the  electroscope,  the  warm  disc 
being  usually  resinous,  and  the  cold  one  vitreous. 

X.  A  stick  of  sealing-wax  broken,  and  the  fractured  portion  applied  to  the 
electroscope,  gives  abundant  evidence  of  electrical  excitation. 

XI.  On  a  sheet  of  mica  place  the  end  of  a  stick  of  sealing-wax  whilst  in 
the  melted  state,  and  as  hot  as  possible;  allow  the  stick  of  wax  to 
cool  and  to  adhere  to  the  mica.  If  now  the  wax  is  suddenly  pulled 
so  as  to  tear  away  a  film,  the  fracture  will  disturb  the  electrical 
quiescence  of  the  mica,  and  it  affects  the  leaves  of  the  electroscope. 

XII.  A  roll  of  sulphur  broken  across,  and  the  bits  powdered  up  in  a  mortar, 

produce  a  very  lively  effect  upon  the  gold  leaves  when  brought  in 
contact  with  the  cap  or  table  of  the  electroscope. 

XIII.  The  crystals  of  tartaric  acid,  boracite,  and  the  tourmaline  all  become 

electrically  excited  when  heated,  and  affect  the  electroscope.  Choco¬ 
late  fresh  from  the  mill,  as  it  curls  in  the  tin  pans  in  which  it  is 
received,  becomes  strongly  electrical.  When  turned  out  of  the  pans, 
it  retains  this  property  for  some  time,  but  soon  loses  it  by  handling. 
Melting  it  again  in  an  iron  ladle,  and  pouring  it  into  the  tin  pans  as 
at  first,  will,  for  once  or  twice,  renew'  the  pow'er ;  but  when  the  mass 
becomes  very  dry,  and  powdery  in  the  ladle,  the  electricity  is  rev  ived 
no  more  by  simple  melting;  but  if  then  a  little  olive  oil  be  added, 
and  mixed  well  with  the  chocolate  in  the  ladle,  on  pouring  it  into 
the  tin  pans,  as  at  first,  it  will  be  found  to  have  completely  recovered 

its  electric  power.  . 

M.  Becquerel’s  experiment  with  heating  the  tourmaline  is  performed 
as  follows  : — The  crystal  of  tourmaline  is  supported  in  a  stirrup  of 
paper,  attached  to  a  few  filaments  of  silk,  hung  on  to  an  insulating 
rod  of  glass,  attached  to  an  upright  pillar,  so  that  it  can  be  moved  up 
or  down.  The  crystal  is  lowered  so  as  nearly  to  touch  a  plate  of  copper, 

10— 2 


244 


ELECTRICITY. 


heated  below  with  a  spirit-lamp ;  and  resting  on  the  plate  is  a  cylin¬ 
drical  glass,  open  top  and  bottom,  like  a  wide  but  short  lamp-glass. 
Two  pieces  of  covered  bent  wire,  each  carrying  a  little  disc  of  gilt 
paper,  are  placed  over  the  top  edge  of  the  cylinder,  and  so  arranged 
that  each  disc  shall  nearly  touch  the  end  of  the  crystal;  or,  better 
still,  the  cylinder  is  perforated  with  two  holes,  opposite  each  other, 
and  the  wires  cemented  in  with  their  discs,  and  made  to  face  the 
poles  or  ends  of  the  tourmaline.  If  each  wire  is  separately  con- 


Fig.  194. — Becquerels  experiment  with  the  heated  Tour?tialine. 

A.  the  suspended  and  heated  tourmaline;  b+,  the  wire  conveying  the  +  or  vitreous  electricity  to 
the  electroscope  c  + ;  b  — ,  convey  mg  the  —  or  negative  electricity  to  the  electroscope  c  — ;  d,  the 
spirit-lamp  heating  the  copper  plate  e. 


nected  with  a  delicate  electroscope  having  very  small  gold  leaves, 
and  the  crystal  warmed  and  then  raised  so  as  to  be  opposite  to  and 
just  touching  the  little  gilt  discs,  one  end  of  the  crystal  will  give 
vitreous  or  -f-  electricity,  the  other  resinous  or  —  electricity.  The 
effect  is  most  powerful  whilst  the  temperature  is  rising;  when  the 
temperature  becomes  fixed,  the  electrical  effect  ceases.  On  reversing 
the  experiment  and  allowing  the  tourmaline  to  cool,  the  electricity 
again  becomes  apparent ;  but  the  electrical  poles  of  the  crystal  are 
reversed,  the  end  that  was  +  whilst  being  heated  becoming  —  in 


EXPERIMENTS  WITH  THE  ELECTROSCOPE. 


245 


the  act  of  cooling.  If  the  crystal  is  broken,  the  fragments,  like  the 
parts  of  a  broken  magnet,  each  exhibits  the  opposite  electricities  at 
their  extremities.  M.  Gaugain  states  that  the  crystal  should  not  be 
heated  beyond  about  302°  F.  If  raised  to  7520  F.,  the  tourmaline 
becomes  a  conductor  of  electricity ;  it  recovers  its  insulating  powet 
on  cooling,  but  is  then  rendered  hygroscopic ;  this  property  it  again 
loses  on  being  washed  and  dried  at  302°  F. 

XIV.  In  the  article  on  Electrical  Induction,  a  still  more  delicate  electroscope 
called  Volta's  condenser  electroscope,  and  another  termed  Pcclet's 
Multiplying  Condenser,  will  be  described.  With  the  first  of  these 
instruments  the  electricity  derived  from  “ chemical  action  ”  is  dis¬ 
tinctly  shown.  A  clean  platinum  capsule,  containing  some  distilled 
water,  is  placed  upon  the  Volta  electroscope;  into  this  is  immersed 
a  plate  of  zinc  connected  by  a  wire  with  the  earth.  The  liquid 
acquires  a  very  feeble  charge  of  -f-  or  positive  electricity,  and  the 
metal  is  found  to  be  —  or  negative  :  the  very  slight  oxidizing  power 
of  the  water  upon  the  zinc  is  supposed  to  produce  this  result.  There 
is  no  advantage  gained  by  the  addition  of  a  little  sulphuric  acid, 
because  the  conducting  power  of  the  water  is  increased,  and  the 
two  electricities  have  a  tendency  to  re-unite  directly  they  are 
liberated:  hence  pure  water  is  the  best  for  this  experiment. 

XV.  With  the  same  electroscope  (Volta’s)  the  electricity  eliminated  by 
combustion  may  be  rendered  apparent.  The  carbonic  acid  is  allowed 
to  impinge  upon  a  metallic  plate  placed  in  conducting  communica¬ 
tion  with  the  instrument,  the  charcoal  being  burnt  in  connection  with 
the  earth.  The  electricity  is  extremely  feeble,  but  is  found  to  be 
definite,  the  carbon  being  —  or  negative,  whilst  the  carbonic  acid  is 
+  or  positive.  The  combustion  of  hydrogen  gas  produces  water; 
and  in  this  combination  of  the  former  with  oxygen,  the  hydrogen  is 
found  to  be  —  or  negative,  and  the  steam  +  or  positive. 

XVI.  It  was  contended  by  Pouillet — to  whom  we  are  indebted  for  a  large 
number  of  these  delicate  experiments— that  when  water  is  evaporated 
electricity  is  always  liberated ;  if  the  water  was  alkaline,  it  charged 
the  electroscope  with  positive,  if  acid,  with  negative  electricity; 
hence  it  was  easy,  and  seemed  feasible,  to  propose  a  theory  which 
should  account  for  the  accumulation  of  electricity  in  the  clouds, 
the  enormous  amount  of  evaporation  going  on  from  the  surface  of 
rivers,  lakes,  seas,  being  supposed  to  be  a  constant  source  of  electric 
power.  Peltier  has  shown  that  the  electrical  effects  are  most  likely 
due  to  friction  of  the  evaporating  fluid  against  the  sides  of  the  vessel, 
as  the  electricity  is  only  liberated  at  the  last  moment,  when  the  alka¬ 
line  matter  is  crackling  against  -the  vessel  in  the  act  of  becoming 
solid.  Moreover  Faraday  demonstrated  that  the  steady  evaporation 
of  water  from  a  platinum  dish  did  not  produce  electricity ;  if,  however, 
the  dish  was  made  very  hot,  and  a  large  drop  of  water  allowed  to 
fall  into  it,  the  latter  assumed  the  spheroidal  state,  and  no  electricity 
was  apparent  until  the  temperature  of  the  platinum  dish  was  allowed 
to  fall,  and  the  drop  of  water  to  boil  violently  and  to  rub  against  the 
sides  of  the  vessel.  It  will  be  seen  presently  that  the  further  dev'clop- 
ment  of  this  idea  led  to  the  construction  of  the  powerful  steam  hydro¬ 
electric  machine  at  the  Polytechnic  Institution. 


246 


ELECTRICITY. 


XVII.  The  slow  oxidation  of  zinc  by  the  air  has  been  used  by  De  Luc,  who 
contrived  the  dry  pile.  The  dry  pile  is,  however,  useless  if  allowed 
really  to  become  dry ;  it  has  been  found  that,  when  the  moisture 
naturally  present  in  all  paper  is  thoroughly  removed,  the  action  of 
the  dry  pile  diminishes  and  almost  ceases,  but  is  easily  restored 
by  the  admission  of  damp  air,  which  gives  back  to  the  paper  its 
natural  amount  of  moisture.  The  dry  pile  is  usually  made  by 
arranging,  in  a  tube  capped  at  both  ends  with  brass,  discs  of  thin 
sheet-zinc  paper  or  silver-foil,  and  the  following  are  Mr.  Singer’s 
directions  for  the  construction  of  a  dry  pile : 

The  materials  I  prefer  for  these  piles  are  thin  plates  of  flatted 
zinc,  alternating  with  writing  or  smooth  cartridge  paper  and  silver 
leaf. 

u  The  silver  leaf  is  first  laid  on  paper,  so  as  to  form  silvered  paper, 
which  is  afterwards  cut  into  small  round  plates  by  means  of  a  hollow 
punch. 

“  In  the  same  way  an  equal  number  of  plates  are  cut  from  thin 
flatted  zinc  and  from  common  writing-paper. 

“  These  plates  are  then  arranged  in  the  order  of  zinc  paper,  silvered 
paper  with  the  silver  side  upwards,  zinc  upon  the  silver,  the  paper, 
and  again  silvered  paper  with  the  silvered  side  upwards,  and  so  on ; 
the  silver  being  in  contact  with  zinc  throughout,  and  each  pair  of  zinc 
and  silvered  plates  separated  from  the  next  pair  by  two  discs  of  paper. 

“  An  extensive  arrangement  of  this  kind  may  be  placed  between 
three  thin  glass  rods,  covered  with  sealing-wax,  and  secured  in  a  tri¬ 
angle  by  being  cemented  at  each  end  into  three  equidistant  holes  in 
a  round  piece  of  wood ;  or  the  plates  may  be  introduced  into  a  glass 
tube,  previously  well  dried,  and  having  its  end  covered  with  sealing- 
wax  and  capped  with  brass ;  one  of  the  brass  caps  may  be  cemented 
on  before  the  plates  are  introduced  into  the  tube,  and  the  other  after¬ 
wards.  Each  cap  should  have  a  screw  pass  through  its  centre,  which 
terminates  in  a  hook  outside.  This  screw'  serves  to  press  the  plates 
closer  together,  and  to  secure  a  perfect  metallic  contact  with  the 
extremities  of  the  column.” 


Fig.  195. — De  Luc’s  “ Dry  Pile’’ connected  with  two  Electroscopes. 

If  a  tube  containing  one  thousand  alternations  is  laid  upon  two 
electroscopes,  as  in  Fig.  195,  the  zinc  end  is  found  to  be  positive, 
and  the  silver  negative.  Mr.  Singer  continues  : 

*  I  found  a  series  of  from  tw'elve  to  sixteen  hundred  groups,  which 


EXPERIMENTS  WITH  THE  ELECTROSCOPE. 


247 


are  arranged  in  two  columns  of  equal  length,  which  are  separately 
insulated  in  a  vertical  position :  the  positive  end  of  one  column  is 
placed  lowest,  and  the  negative  end  of  the  other,  their  upper  extremi¬ 
ties  being  connected  by  a  wire,  they  may  be  considered  as  one 
continuous  column.  A  small  ball  is  situated  between  each  extremity 
of  the  column  and  its  insulating  support  ;  a  brass  ball  is  suspended 
by  a  thin  thread  of  raw  silk,  so  as  to  hang  midway  between  the  balls, 
and  at  a  very  small  distance  from  them. 

“  For  this  purpose  the  balls  are  connected  during  the  adjustment 
of  the  pendulum  by  a  wire,  that  their  attraction  may  not  interfere 
with  it ;  and  when  this  wire  is  removed,  the  motion  of  the  pendulum 
commences.  The  whole  appararus  is  placed 
upon  a  circular  mahogany  base,  in  which  a 
groove  is  turned  to  receive  the  lower  edge 
of  a  glass  shade,  with  which  the  whole  is 
covered.” 

Mr.  Singer  directs  that,  in  order  to  preserve 
the  power  of  the  columns,  the  two  ends  should 
never  be  connected  by  a  conducting  sub¬ 
stance  for  any  length  of  time.  It  is  there¬ 
fore  necessary,  when  laid  by,  that  it  should 
be  placed  upon  two  sticks  of  sealing-wax,  and 
that  the  terminal  balls  be  half  an  inch  or  so 
from  the  table. 

If  a  column  which  appears  to  have  lost  its 
power  be  thus  insulated  for  a  few  days,  it  will 
recover.  There  is  another  cause  of  deteriora¬ 
tion,  which  is  more  fatal:  this  is  too  much 
moisture.  The  paper  discs  therefore  should 
be  made  as  hot  as  possible  before  they  are 
put  together  ;  or  even  subjected  to  a  con¬ 
tinued  but  gentle  heat  for  some  time  before 
they  are  inclosed  in  the  glass  tube,  and,  that 
being  heated  also,  the  plates  may  be  inclosed 
without  the  presence  of  any  appreciable  moisture. 

The  size  of  the  plates  may  be  fths  of  an  inch  in  diameter,  or  less. 

With  a  column  of  20,000  alternations  a  Leyden  jar  may  be  charged, 
and  minute  sparks  are  visible  when  contact  is  made  with  the  fine 
points  of  wire  connecting  the  two  extremities. 

When  the  dry  pile  is  attached  to  the  electroscope  of  Hare  by  sub¬ 
stituting  the  poles  of  two  of  De  Luc’s  columns  for  the  gilt  disc  (fig. 
193,  p.  212),  the  instrument  is  made  wonderfully  delicate,  so  much  so 
that  Mr.  Sturgeon  describes  an  arrangement  of  this  kind,  the  delicacy 
of  which  he  states  to  be  such  that,  the  cap  being  of  zinc,  and  ot  the 
size  of  a  sixpence,  the  pendent  leaf  is  caused  to  lean  towards  the 
negative  pole  by  merely  pressing  a  plate  of  copper,  also  the  size  of  a 
sixpence,  upon  it,  and  when  the  copper  is  suddenly  lifted  up  the 
leaf  strikes.  The  different  electrical  states  of  the  inside  and  outside 
of  various  articles  of  clothing  were  readily  ascertained  by  this  deli¬ 
cate  electroscope.  Bohnenberger  has  the  credit  ol  making  the  first 
of  these  instruments. 


Fig.  196. 

The  Perpetual  Chime , 
constructed  with  De 
Luc’s  columns. 


248 


ELECTRICITY. 


Fig.  197. — Bohnenberger1  s 
Electroscope. 


The  gold  leaf,  being  in  equilibrium,  and  neither 
attracted  or  repelled,  is  instantly  moved  to  one 
side  or  the  other  when  the  very  smallest  amount 
of  electricity  is  evolved  on  the  cap  of  the  instru¬ 
ment. 

From  these  various  experiments  with  electro¬ 
scopes  it  may  be  learned  that  friction  under  every 
circumstance,  and  even  when  disguised,  as  in  the 
rapid  evaporation  of  water  from  a  hot  surface,  is 
an  important  source  of  electricity; 

That  there  are  two  kinds  or  conditions  of  elec¬ 
tricity  which  exactly  neutralize  each  other,  and 
they  are  always  evolved  together; 

That  pressure,  or  any  modification  of  mecha¬ 
nical  motion,  such  as  fracture,  rending,  or  tear¬ 
ing,  all  cause  electrical  quiescence  to  be  dis¬ 
turbed  ; 

That  heat,  as  applied  to  various  crystals,  sets 
their  particles  in  motion,  and  causes  the  evolu¬ 
tion  of  electric  force ; 

That  chemical  action  is  a  source  of  electricity, 
of  a  tension  similar,  though  not  equal,  to  that  of 
ordinary  friction,  as  shown  in  De  Luc’s  column. 


A,  the  gold-leaf  suspended  between  the  two  poles,  b  b,  of  the  dry  pile. 


ELECTRICAL  MACHINES. 

In  the  year  1777,  Tiberius  Cavallo,  a  thoroughly  practical  and  learned  elec¬ 
trician,  describes,  in  his  “  Complete  Treatise  on  Electricity,”  the  construction 
of  the  cylinder  electrical  machine  of  his  day.  It  will  not  be  found  to  differ 
materially  from  that  made  in  1868.  He  remarks — 

“ }  he  principal  parts  of  the  electric  machine  are  the  electric,  the  moving 
engine,  the  rubber,  and  the  prime  conductor,  i.e.,  an  insulated  conductor  which 
immediately  receives  the  electricity  from  the  excited  electric.” 

d  he  electric  formerly  used  was  made  of  different  substances,  as  glass,  resin, 
sulphur,  sealing-wax,  &c.;  and  in  different  forms,  as  cylinders,  globes,  sphe¬ 
roids,  &c.  (Fig.  198.) 

1  he  three  glass  globes  are  made  to  rotate  and  rub  against  three  cushions. 
The  conductor,  a  piece  of  metallic  pipe  or  a  gun-barrel,  was  suspended  from 
the  ceiling  by  silken  cords,  and  connected  with  the  globes  by  unravelled  gold 
lace  hanging  down,  the  latter  being  used  for  the  same  purpose  as  the  points 
now  attached  to  all  conductors  of  electrical  machines. 

This  diversity,  ’  continues  Cavallo,  speaking  of  the  various  shapes  and 
nature  of  the  electric  used,  “then  obtained  on  two  accounts:  first,  because  it 
'vas  n°f  ascertained  which  substance  or  form  would  answer  best;  and,  secondly, 
on  account  of  producing  a  negative  or  positive  electricity  at  the  pleasure  of 
the  operator ;  for,  before  the  electricity  of  the  insulated  rubber  was  discovered, 
su  p  tur,  rough  glass,  or  sealing-wax  was  generally  used  for  the  negative  e'.ec- 


ELECTRICAL  MACHINES. 


>49 


Fig.  198. — Dr.  Watson's  Electrical  Machine, 

showing  the  first  application  of  the  cushion  as  a  rubber,  instead  of  the  hand. 


tricity.”  The  reader  will  perceive  that  Cavallo  adopts  the  Franklinian  theory. 
“  At  present  smooth  glass  only  is  used ;  for,  when  the  machine  has  an  insu¬ 
lated  rubber,  the  operator  may  produce  positive  or  negative  electricity  at  his 
pleasure,  without  changing  the  electric. 

“  In  regard  to  the  form  of  the  glass,  those  commonly  used  at  present  are 
globes  and  cylinders. 

“The  cylinders  are  made  with  two  necks;  they  are  used  to  the  greatest 
advantage  without  any  axis  (or  rod  passed  through  from  neck  to  neck);  and 
their  common  size  is  from  4  in.  diameter  and  8  in.  long  to  12  in.  diameter  and 
2  ft.  long,  which  arc  perhaps  as  large  as  the  workmen  can  conveniently  make 

them. 

“  The  glass  generally  used  is  the  best  flint,  though  it  is  not  yet  absolutely 
determined  which  kind  of  metal  is  the  best  for  electrical  globes  and  cylinders. 
The  thickness  of  the  glass  seems  immaterial,  but  perhaps  the  thinnest  is 
preferable. 

“  It  has  often  happened  that  glass  globes  and  cylinders  in  the  act  of  whirling 
have  burst  in  innumerable  pieces  with  great  violence,  and  with  some  danger 
to  the  bystanders.  Those  accidents  are  supposed  to  happen  when  the  globes 
and  cylinders,  after  being  blown,  arc  suddenly  cooled. 

“  It  will,  therefore,”  prudently  remarks  Cavallo,  “be  necessary  to  enjoin  the 
workmen  to  let  them  pass  gradually  from  the  heat  of  the  glass-house  to  the 
atmospherical  temperature.” 

The  author  prefers  a  single  handle,  instead  of  the  multiplying  gear,  which 
is  very  apt  to  get  out  of  order,  and  the  cord  to  stretch  or  break  when  most 


25° 


ELECTRICITY. 


wanted.  The  various  parts  of  the  machine  just  described  were  gradually  in¬ 
vented  and  applied  by  various  clever  electricians, —  Oito  Guericke,  Hawkesbee, 
Abbe  Nollet,  Dr.  Watson,  Wilson,  Nairne,  Dr.  Priestley;  and  many  years 
elapsed  before  the  machine  attained  anything  like  the  perfection  of  that  em- 


Fig.  199. — Cylinder  Electrical  Machine ,  used  by  Cavallo  in  1 777, 

Showing  the  glass  cylinder  a  a,  with  a  pulley  attached  to  one  neck.  B.  round  which  an  endless  cord 
passes  to  a  latge  or  multiplying  wheel,  C;  the  cushion  e,  and  silk  flap  f-  the  cushion,  placed 
on  a  glass  pillar  let  into  a  piece  of  wood,  moves  backwards  and  forwards  in  a  groove,  G,  and  is  se¬ 
cured  by  a  screw  ;  before  use,  is  covered  with  amalgam  The  machine  is  clamped  to  the  table  at  H. 
The  prime  conductor  i  i,  with  collecting  points  k,  is  supported  on  glass  legs,  L  L,  let  into  a  maho¬ 
gany  stand  '['lie  amalgam  used  by  Cavallo  consisted  of  two  parts  mercury  and  one  of  tinfoil,  with 
a  little  powdered  chalk,  all  rubbed  up  with  grease. 


ployed  by  Cavallo  in  his  experiments.  A  more  elegant  and  compact  form  is 
now  given  to  the  cylinder  machine  by  Messrs.  Elliott,  of  the  Strand. 

The  most  convenient  form  is  undoubtedly  the  plate  electrical  machine.  Of 
this  Cavallo  says — 

“Next  to  Dr.  Priestley’s  machine,  I  shall  describe  another,  which  was 
invented  by  Dr.  Igenhouz,  and  which,  from  its  simplicity  and  conciseness, 
makes  a  fine  contrast  with  the  former. 

1  his  machine  consists  of  a  circular  glass  plate,  about  1  ft.  in  diameter, 
which  is  turned  vertically  by  a  winch  fixed  to  the  iron  axis  that  passes  through 
its  middle;  and  it  is  rubbed  with  four  cushions,  each  about  2  in.  long,  situated 
at  the  opposite  ends  of  the  vertical  diameter.” 

Fig.  200  is  a  drawing  of  the  large  plate  electrical  machine  in  use  at  the 
Polytechnic.  1  he  plate  glass  is  7  ft.  in  diameter,  and  rather  more  than  |ths 
of  an  inch  thick ;  it  has  two  large  rubbers,  and,  when  these  are  well  amalga¬ 
mated,  and  the  weather  is  propitious — at  least  dry — very  long  sparks  of  great 
intensity  may  be  obtained;  when  the  atmosphere  is  damp,  in  spite  of  the 
rapidity  and  power  with  which  it  is  turned  round  by  a  four-horse  power  steam 
engine,  it  will  hardly  give  a  spark  an  inch  in  length. 

The  prime  conductor  is  a  large  globe,  about  3  ft.  in  diameter;  and  inserted 
into  this  is  a  large  ring  of  wood,  4  ft.  in  diameter,  and  raised  6  ft.  from  the 
globe  being  an  arrangement  first  proposed  in  connection  with  the  Austrian 
electrical  machines  exhibited  in  the  Great  Exhibition  of  1862.  The  ring,  no 
doubt,  theoretically  speaking,  should  act  as  a  condenser,  and  assist,  by  induc¬ 
tion,  to  increase  the  tension  of  the  electricity ;  but  whether  it  be  due  to  the 


ELECTRICAL  MACHINES. 


25J 


Fig.  200. —  The  great  Plate  Electrical  Machine  at  the  Royal  Polytechnic. 


height  of  the  building  in  which  the  ring  is  placed,  or  from  other  causes,  the 
effect  produced  did  not  appear  to  be  increased  by  this  addition  to  the  apparatus. 
The  power  of  an  electrical  machine  is  greatly  influenced  by  the  nature  of  the 
glass.  There  is  a  very  fine-looking  machine  at  the  Polytechnic,  constructed 
on  the  plan  of  the  late  Sir  William  Snow  Harris:  the  plate  is  3  ft.  in 
diameter ;  but,  in  consequence  of  the  alkali  of  the  plate  glass,  its  power  is 
very  slight,  and  not  half  so  good  as  that  of  many  small  cylindrical  machines. 

The  best  amalgam  for  an  electrical  machine  is  made  of  1  part  of  tin,  2  of 
zinc,  and  6  of  mercury.  Melt  the  zinc  and  tin  together,  and,  when  approaching 
solidification,  add  the  mercury,  and  stir  till  the  whole  is  solid  :  if  the  latter  is 
added  when  the  alloy  of  zinc  and  tin  is  too  hot,  much  of  it  may  be  dissipated 
in  vapour ;  and  the  amalgam  should  be  made  under  a  chimney,  to  avoid  the 
fumes  of  mercury.  Sometimes  the  above  are  rapidly  melted  together,  and 
then  placed  in  a  wooden  box  and  shaken  until  quite  cold.  The  shaking 
reduces  the  greater  part  to  a  line  powder,  which  may  lie  sifted  out  and  used 


252 


ELECTRICITY. 


with  grease.  The  author  always  lays  a  coating  of  tallow-grease  on  the 
cushion  first,  and  then  carefully  sifts  the  amalgam  upon  it,  laying  all  smooth 
with  a  clean  broad  knife  or  spatula. 

Very  cheap  machines  can  be  made  from  common  window-glass,  to  the 
centre  of  which,  and  on  the  opposite  sides,  two  wooden  caps,  turned  convex, 
may  be  cemented  without  any  perforation  of  the  plate,  the  axle  being  made 
of  glass  rod  fitting  into  holes  in  the  wooden  caps.  Mr.  Goodman  recom¬ 
mends  that  the  cement  used  should  be  made  ot  equal  parts  of  black  resin 
and  beeswax;  but  the  writer  recommends  the  use  of  less  beeswax,  because 
it  renders  the  cement  liable  to  melt  easily  if  the  electrical  machine  is  placed 
before  a  fire  to  be  warmed;  the  quantity  may  be  I  lb.  of  black  resin  to  3  oz. 
or  qoz.,  at  the  most,  of  beeswax.  A  plate  of  this  kind  would  cost  half-a-crown. 
Sometimes  two  circles  of  common  window-glass  are  cemented  together  to 
increase  the  thickness,  and  prevent  the  chance  of  breakage.  The  common 
window-glass,  from  its  hardness,  gives  a  large  quantity  of  electricity  when 
the  friction  is  properly  and  equally  applied.  Very  excellent  machines  are 
now  made  of  plates  of  vulcanite,  and,  in  fact,  are  used  for  mining  purposes. 
The  plate  is  enclosed  in  a  box  of  vulcanite,  and  turned  by  a  handle  on  the 
outside.  It  contains  one  or  more  Leyden  plates;  and  after  these  are  charged 
by  a  few  turns  of  the  machine,  the  discharge  may  be  sent  through  covered 

wire  into  one  of  Professor  Abel’s  fuses 
at  a  distance  of  many  hundred  yards. 
The  writer  has  used  such  a  machine 
on  a  damp  night  in  November,  in  the 
grounds  of  Haileybury  College,  Herts, 
with  the  greatest  success,  exploding 
three  separate  charges — one  of  gun¬ 
powder,  directed  against  a  heavy  gate; 
another,  a  mine,  blowing  many  tons 
of  earth  into  the  air;  and  a  third,  a 
keg  of  9  lbs.  of  gun-cotton,  made  by 
Messrs.  Prentice,  of  Stowmarket, 
which  nearly  emptied  a  pond  in  which 
it  was  exploded,  and,  sad  to  relate, 
broke  a  great  many  windows  in  the 
chapel  by  the  terrific  concussion  of 
the  air,  although  the  building  was  at 
least  three  hundred  yards  from  the 
pond  where  the  explosion  took  place. 
Mr.  Hart,  of  Edinburgh,  describes  a 
very  compact  and  well-arranged  ma¬ 
chine,  called  Winter’s  Electrical  Ma¬ 
chine. 

Winter’s  Electrical  Machine  is  one 
of  the  most  perfect  forms  of  the  plate 
friction  machine  that  has  hitherto 
been  made.  It  distinguishes  itself  from 
other  machines  by  the  extraordinary  length  of  the  spark  that  it  gives,  by  sim¬ 
plicity  of  construction,  and  by  the  uniformly  good  results  that  are  obtained 
from  it,  even  when  the  state  of  the  air  is  not  favourable  to  the  display  of  electrical 
phenomena.  The  annexed  drawing  represents  one  of  these  instruments.  It 


Fig.  201. 

Winter’s  Electrical  Machine. 


ELECTRICAL  MACHINES. 


253 


will  be  seen  from  it  that  the  glass  plate  is  fixed  into  an  axle,  which  revolves  in 
two  upright  supports.  One  of  these,  in  which  the  shorter  wooden  end  of  the 
axle  revolves,  is  made  of  glass,  and  the  other,  in  which  the  longer  glass  end 
of  the  axle  revolves,  is  made  of  wood.  By  this  means  the  electricity  formed 
upon  the  plate  cannot  on  either  side  reach  the  ground,  for  on  the  one  side  the 
insulating  glass  pillar,  and  on  the  other  the  insulating  glass  axle,  prevents  it, 
and  thus  complete  insulation  of  the  plate  forms  one  of  the  elements  of  the  ex¬ 
cellence  of  Winter’s  machine.  The  friction  in  this,  as  well  as  in  all  friction- 
machines,  is  caused  by  pressing  on  the  plate  of  glass  a  flat  surface  of  leather, 
covered  with  an  amalgam  of  mercury,  zinc,  and  tin,  which  is  put  on  with 
the  aid  of  a  little  grease.  The  frame  standing  on  the  low  glass  support  to 
the  right  of  the  figure  is  the  wooden  rubber  frame,  into  the  notches  of 
which  fit  two  flat  pieces  of  wood  covered  in  front  or  on  the  side  next  the  plate 
with  leather  and  a  very  little  stuffing,  and  provided  on  the  other  side  with 
springs,  which,  acting  against  the  frame,  keep  the  front  surface  uniformly 
pressing  against  the  plate.  There  is  only  one  pair  of  rubbers,  not  two,  as  in 
ordinary  machines,  and  this  enables  them  to  be  placed  at  a  greater  distance 
from  the  prime  conductor  of  the  machine.  The  brass  ball  standing  on  the 
tall  glass  support  to  the  left  is  the  prime  conductor.  For  the  sake  of  more 
perfect  insulation,  this  ball  is  fitted  on  to  the  support  by  means  of  a  trumpet¬ 
shaped  opening  made  in  it,  thereby  preventing  the  dispersion  of  electricity  that 
would  arise  from  the  sharp  edge  of  a  hole  exactly  large  enough  for  the  rod. 
There  are  three  other  openings  in  this  ball,  one  on  each  side  and  one  at  the 
top.  The  two  small  rings  which  are  seen  projecting  upon  the  plate  fit  into 
one  of  these  by  means  of  a  T-shaped  piece  of  brass.  They  are  made  of  wood, 
and  have  a  groove  cut  in  them  on  the  side  turned  towards  the  plate,  into  which 
a  row  of  fine  pin-points  is  fixed  for  collecting  the  electricity  formed  upon  it. 
These  points  are  connected  with  the  prime  conductor  by  means  of  a  strip  of 
tinfoil  which  lines  the  bottom  of  the  groove.  Two  wings  of  oiled  silk  attached 
to  the  rubbers  stretch  between  them  and  these  rings,  so  as  to  prevent  the 
electricity  from  dissipating  itself  before  reaching  them.  The  opening  on  the 
top  of  the  ball  is  made  to  receive  the  stalk  of  the  large  wooden  ring,  which  is 
seen  surmounting  it,  and  which  forms  the  most  peculiar  feature  of  the  instru¬ 
ment.  An  iron  wire  forms  the  core  of  this  ring,  and  is  in  metallic  connection 
with  the  prime  conductor.  The  function  performed  by  this  remarkable  appen¬ 
dage  is  to  lengthen  the  sparks  given  by  the  machine.  In  a  24  in.  plate,  for 
instance,  with  the  aid  of  the  ring,  the  sparks  are  14  in.  in  length,  and  without 
it  scarcely  two.  The  remaining  opening  in  the  prime  conductor  is  for  the 
stalk  of  the  small  brass  ball  from  which  the  sparks  are  obtained.  Io  the  left 
of  the  figure  is  the  spark-drawer  for  receiving  the  sparks  from  the  machine. 
The  length  of  the  spark  given  by  an  electrical  machine  is  by  far  the  most 
severe  test  of  the  excellence  of  its  construction,  and,  in  this  respect.  Winter’s 
machine  is  entitled  to  hold  the  first  rank  among  friction-machines.  A  machine 
12  in.  in  diameter  costs  £5. 

Another  and  most  interesting  electrical  machine,  by  which  the  apparent 
anomaly  of  frictional  electricity  without  friction  is  realised,  was  exhibited  in 
the  Great  French  Exhibition  of  1867,  and  described  by  a  careful  observer,  in 
the  ‘  Mining  Journal.’ 

“In  appearance,  Holtz’s  machine  resembles  the  ordinary  plate  machine; 
in  fact,  the  most  prominent  part  is  a  glass  disc,  which  is  mounted  and 
revolved  in  the  usual  manner.  But  the  plate  is  thinner  the  thinner  the 


254 


ELECTRICITY. 


Fig.  202.  —  The  Holts  Electrical  Machine ,  giving  “ frictional  electricity  ” 

without  friction. 


better — and  as  it  is  desirable  to  revolve  it  very  rapidly,  a  multiplying  wheel 
is  connected  with  the  plate,  so  that  the  speed  may  be  increased  to  the  extent 
desired.  I  he  machine,  however,  has  really  but  little  resemblance  to  the 
plate  machine,  for  it  has  no  rubbers ;  it  produces  torrents  of  frictional  elec¬ 
tricity,  but  the  electricity  is  not  generated  by  friction ;  there  is  no  friction 
about  the  machine,  except  at  the  axle  bearings.  The  plate  revolves  in  free 
air,  and  nothing  should  touch  it.  In  the  place  of  rubbers  are  what  are  called 
inductors,  which  are  strips  of  paper  3  or  4  in.  long,  and  about  1  in.  wide. 
They  are  supported  and  insulated  on  pieces  of  glass,  which  are  of  spear-head 
form.  The  inductor  is  made  complete  by  oasting  on  to  the  paper  pointed 
pieces  of  cardboard,  which  project  beyond  the  glass  spear- heads  an  inch  or 
two.  T  he  spear-heads  are  attached  to  the  framework  of  the  machine,  so  that 
they  shall  be  parallel,  and  as  near  as  possible,  to  the  plate  on  its  crank  side. 
Opposite  the  inductors,  at  the  front  of  the  plate,  are  the  comb  points,  which 
serve  to  collect  the  electricity,  and  convey  it  to  the  conductors  for  use.  Each 
inductor  is  furnished  with  its  set  of  points.  The  combs  are  attached  to  brass 
rods,  terminated  at  their  other  ends  by  brass  balls.  The  rods  are  fastened 
'to  the  framework  of  the  machine,  and  are  insulated  from  it.  The  balls  at 
the  ends  of  the  rods  may  be  connected  to  each  other  in  any  desired  order  by 
means  of  bent  wires. 

1  o  obtain  the  electricity,  one  of  the  inductors  is  slightly  charged,  by 
means  of  an  excited  rod  of  hard  rubber,  glass  tube,  or  otherwise,  and  turning 
the  crank.  Its  power  progressively  increases  for  about  a  minute,  and  until  it 
reaches  the  maximum,  when  it  furnishes  a  stead)  supply  of  electricity  as  long 


ELECTRICAL  ATTRACTION. 


255 


as  the  disc  is  revolved.  The  amount  of  electricity  which  a  disc  of  only  2  ft. 
in  diameter  will  yield  is  enormous. 

“  To  explain  the  action  of  the  machine  three  elements  must  be  considered 
—the  inductor,  the  plate,  and  the  comb  points.  If  a  pointed  wire  be  brought 
opposite  an  electrified  body — as,  for  example,  a  prime  conductor — the  positive 
electricity  of  the  prime  conductor  attracts  the  negative  of  the  wire,  and  repels 
its  positive,  and  a  stream  of  negative  electricity  flows  out  of  the  wire  at  its 
point,  whde  the  positive  flows  to  the  opposite  direction.  Now,  suppose  a 
sheet  of  glass  be  interposed  between  the  point  and  the  conductor.  The 
attraction  of  the  positive  electricity  of  the  conductor  for  the  negative  of  the 
wire  is  by  no  means  lessened;  the  negative  is  accumulated  towards  the  point, 
and,  by  reason  of  its  higher  tension,  flows  out  on  to  the  glass.  But  the  glass 
is  impervious  to  the  electricity,  and  it  remains  on  its  surface;  the  glass 
becomes  electrified.  In  Professor  Holtz’s  machine  we  have  the  electrified 
body  in  the  inductor,  the  wire  point  opposite,  and  the  glass  plate  interposed. 
Suppose  inductor  No.  1  electrified  positively,  this  positive  electricity  attracts 
negative  electricity  out  of  the  comb  points  on  to  the  interposed  plate.  The 
plate  moving  on  the  part  electrified  negatively  comes  opposite  card  points  of 
inductor  No.  2.  Here  the  negative  electricity  of  the  plate  draws  out  of  the 
card  points  positive  electricity  on  to  the  glass,  and  inductor  No.  2  becomes 
charged  negatively,  while  the  glass  is  negatively  charged  on  the  further  side, 
and  positively  charged  on  the  near  side.  Inductor  No.  2,  being  charged 
negatively,  draws  positive  electricity  out  of  comb  points  No.  2,  and  neutra¬ 
lizes  the  negative  drawn  from  comb  points  No.  1.  Card  points  No.  3  dis¬ 
charge  negative  electricity  on  the  plate,  and  inductor  No.  3  becomes  positive, 
and,  like  No.  1,  draws  negative  electricity  out  of  the  corresponding  comb 
point.  It  will  be  seen  that  the  alternate  inductors  are  oppositely  electrified, 
and  that  their  corresponding  comb  points  give  out  or  receive  accordingly. 
By  varying  the  manner  of  connecting  the  balls  at  the  extremities  of  the  comb 
points  a  considerable  variety  of  changes  in  the  relation  of  the  quantity  and 
intensity  may  be  obtained.  These  variations  are  somewhat  similar  to  those 
which  are  secured  by  varying  the  order  of  connecting  the  elements  ot  the 
galvanic  battery.  The  greatest  intensity  is  obtained  by  connecting  the 
inductors  as  they  stand  in  numerical  order  round  the  disc.  By  connecting 
one  of  the  poles  with  the  ground,  the  other  may  be  used  as  a  prime  conductor 
for  charging  Leyden  jars,  &c.  It  is  found  advisable,  in  order  to  secure  more 
perfect  insulation,  to  varnish  the  plate  and  the  inductors  with  shellac  varnish.” 


- ♦- - - 

ELECTRICAL  ATTRACTION  AND  REPULSION  GOVERNED  BY 

CERTAIN  LAWS. 

The  electroscopes  already  described  are  merely  intended  to  indicate  the 
development  of  electricity  ;  their  construction  does  not  permit  any  calculation 
to  be  made  as  to  the  quantity  of  the  force  present  in  or  upon  any  given  surface. 

In  using  a  common  magnet  to  attract  a  needle,  it  is  evident  that  distance 
regulates  the  intensity  of  the  power,  which  increases  rapidly  as  the  two  are 
brought  in  closer  proximity,  or  decreases  as  quickly  by  increasing  the  distance 
between  them. 


256 


ELECTRICITY. 


The  influence  of  distance  is  particularly  shown  in  experiments  with  static 
electricity,  and  the  phenomena  were  carefully  examined  by  Coulomb,  who 
determined  the  laws  which  bear  his  name. 

First  Law  of  Coulomb. — Two  electrified  bodies  attract  or  repel  each  other 
with  a  force  which  is  inversely  proportional  to  the  square  of  the  distance  that 
separates  them. 

Example  :  An  electrified  body  at  a  certain  distance  exerts  a  force  which 
may  be  called  unity  or  one;  at  half  that  distance  the  power  is  four  times 
greater  ;  at  one-third,  nine  times ;  one-fourth,  sixteen  times  greater,  and  so  on. 

Second  Law. — The  distance  remaining  the  same,  the  attractions  or  repul¬ 
sions  are  in  the  compound  ratio  to  the  quantities  of  electricity  which  the  two 
bodies  possess. 

Example:  A  fixed  electrified  ball,  which  will  repel  another  and  movable  one 
to  a  certain  distance,  called  unity  or  one,  will  have  only  half  the  power  if  con¬ 
nected  with  another  ball  of  the  same  size,  the  charge  distributed  over  one 
surface  is  now  spread  over  double  the  surface;  and  if  this  again  is  connected 
with  another  ball,  the  force  is  halved  again,  and  possesses  only  a  quarter  of 
its  original  power. 


Fig.  203. 

A  an  insulated  ball  electrized  with  a  force  to  be  called  unity,  1  ;  A  B,  the  same  ball  touching  another 
ball  of  the  same  size,  B.  The  charge  is  now  spread  oxer  twice  the  surface,  and  the  force  is  reduced 
one-half,  b,  the  bail  with  one-h  If  the  charge  ;  b  c,  the  same  ball  touching  another,  c.  The  original 
charge  is  again  spread  over  twice  the  surface,  and  the  force  reduced  at  a  b  to  one-half  is  now  reduced 
at  b  c  to  a  quarter. 


On  the  same  principle,  by  reversing  the  previous  experiments  and  increasing 
the  charge,  if  a  series  of  balls,  gradually  decreasing  in  size,  are  attached  to 
any  given-sized  ball,  they  must  end  in  a  very  small  ball,  or  that  to  which  it  is 
equivalent,  viz.,  a  point ;  consequently  the  charge  increases  in  intensity,  instead 
ot  diminishing  :  and  hence  the  use  of  points,  which  discharge  electricity  very 
rapidly ;  or  receive  it,  as  in  the  points  attached  to  the  prime  conductor  of  an 
ordinary  electrical  machine.  The  electric  force  tends  to  escape  from  the  sur¬ 
face  of  conductors  by  virtue  of  the  repulsion  of  its  own  particles. 

1  he  force  it  exerts  is  considered  proportional  to  the  square  of  the  quantity; 
hence,  if  the  accumulation  of  electricity  in  eight  balls  decreasing  in  size  be 
taken  as  1,2,  3,  4,  5,  6,  7,  8,  the  force  will  be  the  square,  as  shown  in  Fig.  204. 

1  he  last  ball,  which  is  eight  times  less  in  area  than  the  first,  is  charged  eight 
times  more  than  the  first,  and  the  force,  or  desire  to  escape  or  polarize  the 
surrounding  particles  of  air,  is  increased  bv  the  square,  viz.,  sixty-four  times. 


ELECTRICAL  ATTRACTION. 


257 


Fig.  204. —  The  rationale  of  a  Point,  and  why  it  gives  off  Electricity. 

The  lines  show  how  a  point  is  arrived  at  fr  >m  a  eeries  of  spheres  gradually  decreasing  in  size. 


These  laws,  and  the  applications  which  flow  from  them,  were  discovered  by 
Coulomb  with  the  very  delicate  instrument  called  the  Torsion  Electrometer,  or 
Torsion  Balance  (Fig.  205).  It  consists  of  a  cylindrical  or  cubical  glass  box, 
carrying  upon,  but  communicating  through,  the  upper  pane  of  glass  a  vertical 
tube  15  or  20  in.  high.  The  box  may  be  12  in.  high. 


Fig.  205. 

At  the  top  of  the  tube  is  a  graduated  circle  and  pointer,  and  inside  this,  and 
exactly  in  the  centre,  is  attached  a  fine  silver  or  platinum  wire,  stretched  by  a 
little  weight. 

The  wire  suspended  from  the  top  of  the  tube  is  long  enough  to  reach  to  the 
centre  of  the  box;  and  through  the  weight  that  stretches  it  is  passed  a  hori¬ 
zontal  needle  of  gum  lac  or  glass.  The  needle  is  not  suspended  like  a  balance ; 
but  one  arm  is  longer  than  the  other,  and  carries  a  little  disc  of  gold  paper  or 
a  small  gilt  pith-ball. 

In  order  to  measure  the  space  traversed  by  the  needle,  a  proper  scale  is 

17 


ELECTRICITY. 


>5* 


placed  in  the  centre  of  the  front  glass  pane;  and,  before  commencing  experi¬ 
ments,  the  zero  of  the  circle  carried  by  the  tube  is  made  to  correspond  with 
the  zero  of  the  scale  in  the  box ;  and  this  can  be  done  by  carefully  moving 
round  the  top  scale,  to  the  inside  of  which  is  attached  the  metallic  wire  carry¬ 
ing  the  little  weight  and  needle. 

The  needle  is  affected  by  the  electricity  from  a  ball  or  disc  of  exactly  the 
same  size  as  that  attached  to  the  needle,  which  is  supported  by  an  insulating 
stem.  It  is  introduced  vertically  in  another  hole  made  through  the  top  pane 
of  glass,  and  the  whole  is  so  arranged  that,  when  the  ball  of  the  needle  is  in 
contact  with  the  other,  the  needle  is  in  the  direction  corresponding  to  the  zero 
or  o°  of  the  two  scales. 

In  the  cylindrical  glass  Coulomb  balance  the  vertical  ball  is  suspended 
by  a  metallic  rod,  which  goes  through  the  top,  and  is  attached  to  another  ball. 
It  is  not  then  removed  as  in  the  square-box  balance;  but  a  “proof  plane”  on 
an  insulating  handle  is  applied  to  the  electrified  body  under  examination,  and 
this  is  caused  to  touch  the  outer  ball  of  the  balance. 

In  the  square-box  balance  the  ball  is  removed  by  its  insulating  handle,  and 
the  electrified  body  under  examination  is  touched  with  it,  and  the  ball  placed 
inside  the  box.  According  to  the  first  law,  it  immediately  divides  its  electri¬ 
city  with  the  ball  of  the  needle,  which  latter,  being  repelled,  describes  a  larger 
or  smaller  arc,  according  to  the  intensity  of  the  charge. 

Directly  the  needle  is  repelled,  the  wire  must  be  twisted ;  and  this  is  called 
the  force  of  torsion.  Coulomb  ascertained  that  the  forces  of  torsion  are  propor¬ 
tional  to  the  angles  of  torsion;  or,  in  other  words,  the  force  that  causes  the 
torsion  or  twisting  of  the  wire  is  exactly  proportional  to  the  arc  described  by 
the  needle. 

Supposing  the  needle  to  be  repelled  to  the  distance  of  36°,  in  order  to 
compel  the  needle  to  come  to  180,  the  top  circle  on  the  tube  must  be  moved 
round  126  degrees;  from  which  it  follows  that  the  wire,  if  twisted  180  below 
and  126°  above,  makes  up  a  torsion  equal  to  1440.  Under  the  same  circum¬ 
stances,  to  reduce  the  arc  to  90,  an  angle  of  576°  of  torsion  must  be  used. 
The  relation  of  the  36°,  180,  and  90  are  to  each  other  as  the  angles  of  torsion, 
36°,  1 440,  576°,  or  these  angles  are  to  each  other  as  1  :  4  :  16;  hence,  if  the 
distances  are  to  each  other  as  1  :  | :  5,  the  repulsive  forces  are  to  each  other 
as  1  :  4  :  16,  and  the  first  law  of  Coulomb  is  proved. 

The  late  Sir  William  Snow  Harris  employed  a  delicate  brass  scale-beam, 
suspended  from  a  curved  brass  rod  fixed  to  an  insulating  support;  the  beam 
carried  a  circular  gilded  plane  from  one  arm,  and  the  scale  from  the  other ; 
the  gilded  plane  is  suspended  over  another  plane  of  the  same  size,  which  can 
be  raised  or  depressed  at  pleasure.  The  attraction  between  the  two  planes 
was  estimated  by  the  weights  raised,  and  the  instrument  is  known  as  Harris’s 
Balance  Electrometer  (Fig.  206). 

It  is  with  these  apparatus  (the  bifilar  balance  and  balance  electrometer), 
and  by  greatly  varying  his  experiments,  says  De  la  Rive,  “that  Sir  W.  Harris 
found  that  the  law  of  the  inverse  of  the  square  of  the  distance  is  not  exactly 
sustained,  except  when  the  balls  or  the  discs  are  charged  with  an  equal  quan¬ 
tity  of  electricity,  when  this  quantity  is  not  too  feeble,  and,  finally,  when  the 
angular  distance  that  separates  them  is  greater  than  90. 

Otherwise,  and  especially  if  the  electric  charges  of  the  two  bodies  are  very 
different,  the  force  becomes  the  inverse  of  the  simple  distance,  within  certain 
limits.  The  same  causes  equally  modify  the  second  law,  which  establishes 


ELECTRICAL  ATTRACTION. 


259 


the  relation  existing  between  the  quantities  of  electricity  and  the  attractive  or 
repulsive  forces.  Thus  in  one  experiment,  the  respective  quantities  of  elec¬ 
tricity  being  successively  on  each  of  two  discs  in  turn  i  and  2,  the  corre^ 
sponding  repulsive  forces,  instead  of  being  I  and  4,  were  1  and  5.  This  devia¬ 
tion  from  the  law  was  due  to  the  absolute  intensity  of  the  electricity  being  too 
feeble.  But  it  is  much  more  sensible  when  there  is  inequality  in  the  electric 
charges  of  two  bodies,  and  when  this  inequality  is  very  great. 

“These  numerous  exceptions  to  Coulomb’s  laws  are  in  a  great  part  due  to 
there  occurring  to  electrised  bodies, 
when  in  presence  of  each  other,  impor¬ 
tant  modifications  in  their  electric  state, 
by  the  effect  of  influences  whose  action 
we  shall  study  further  on  —  influences 
which  are  the  more  sensible  as  the  elec¬ 
tric  charges  are  more  different. 

“They  depend  also  upon  its  being 
very'  probable  that  the  laws  in  question 
are  general  only  for  points  almost  ma¬ 
thematical  and  not  for  bodies  of  any 
forms  or  dimensions. 

“  Now  we  conceive  that  they  must  be 
so  when  we  employ,  as  Coulomb  did, 
small  equal  spheres  for  electrised 
bodies;  for,  as  is  demonstrated  in  me¬ 
chanics,  the  action  of  a  sphere  is  always 
the  same  as  that  which  would  be  exer¬ 
cised  by  its  centre,  supposing  all  the 
forces  with  which  the  sphere  is  en¬ 
dowed  were  concentrated  in  this  centre. 

We  see,  therefore,  that  Coulomb’s  laws 
may  be  regarded  as  general  by  restrict¬ 
ing  them  to  the  cases  of  electrised 
molecules  or  points ;  and  that  in  other 
cases  they  maybe  regarded  as  deviating 
less  from  the  truth  as  the  bodies  are  of 
smaller  dimensions,  and  as  the  forms 
approach  more  or  less  the  spherical 
form.” 

When  a  sponge,  or  any  other  porous 
matter,  is  dipped  in  water,  the  latter  is 
taken  up  by  the  whole  mass,  and  dif¬ 
fused  through  it.  Similar  ideas  might 
be  formed  with  respect  to  a  charge  of  electricity—  that  it  spreads  itself  through 
the  whole  body  of  the  conductor  on  which  it  was  rendered  evident;  this,  how¬ 
ever,  is  not  the  case;  the  electricity  arranges  itself  on  the  surface  of  electrified 
bodies. 

Hence  balls  and  cylinders  used  in  the  construction  of  electrical  apparatus, 
such  as  conductors,  are  always  made  hollow  :  solidity  is  not  necessary.  1  he 
most  conclusive  experiment  to  prove  the  fact  already  stated  was  that  made  by 
Coulomb.  Having  insulated  a  sphere  of  metal,  it  was  charged  with  electricity, 
and  on  the  application  of  two  hemispheres,  supported,  of  course,  by  glass  rods, 

17—2 


ELECTRICITY. 


j6o 


the  whole  of  the  charge  was  removed  when  they  were  taken  away  and  applied 
to  an  electroscope ;  whereas  the  original  ball  first  charged  did  not  exhibit  the 
slightest  charge  when  tested  with  the  same  instrument. 


Fig.  207. — Coulomb’s  Experiments ,  showing  the  distribution  of  the  Electricity 
on  the  surface  of  insulated  Conductors. 

The  ball  being  first  electrified,  and  the  hemispheres  applied,  which  remove  the  charge. 


Faraday,  whose  name  is  so  completely  identified  with  the  subject  of  >.  ectri- 
city,  devised  many  clever  experiments  to  show  the  fact. 

One  of  the  best  is  where  he  uses  a  conical  muslin  bag  attached  to  an  insu¬ 
lated  ring.  At  the  apex  of  the  cone,  both 
outside  and  inside  the  net,  is  a  silken  thread 
for  the  purpose  of  turning  it  inside  out. 
When  the  bag  is  charged,  a  “proof  plane,” 
i.e.,  a  metallic  plate  attached  to  a  glass  or 
wax  rod,  or  a  small  disc  of  gilt  paper  fixed 
to  a  thin  rod  of  shellac  or  glass,  is  placed  in 
the  interior,  and  then  applied  to  a  delicate 
electroscope,  which  remains  unaffected. 

If,  however,  the  proof  plane  touches  the 
outside  of  the  bag,  a  charge  is  obtained, 
which  is  rendered  evident  directly  the  elec¬ 
troscope  is  used.  By  turning  the  bag  inside 
out  (whilst  insulated  and  charged)  with  the 
dry  silk  string,  silk  being  a  non-conductor, 
the  condition  is  reversed ;  that  which  was 
Fig.  208.  the  outside  is  now  the  inside,  and  gives  no 

Faraday’s  Experiment  with  the  evidence  of  electrical  excitation,  whilst  that 
conical  Muslin  Bag.  which  was  inside  is  now  outside,  and,  of 


ELECTRICAL  ATTRACTION. 


26 1 


course,  will  deliver  a  charge  to  the  proof  plane.  A  bird,  a  white  mouse,  some 
gunpowder,  and  a  delicate  electroscope,  placed  inside  a  wire-gauze  cover,  such 
as  might  be  used  for  protecting  meat,  standing  on  a  stool  with  glass  legs,  and 
connected  with  the  electrical  machine  when  in  full  action,  will  give  an  abun¬ 
dance  of  sparks  from  the  outside,  which  do  not  affect  the  living  things,  the 
gunpowder,  or  the  electroscope  in  the  slightest  degree. 


Fig.  209. —  The  Mouse ,  the  Bin l,  Gunpowder,  and  Electroscope  under  a  Wire 

Gauze  Cover. 


When  two  gilt  pith-balls,  hanging  side  by  side,  and  suspended  from  an  in¬ 
sulating  stand,  are  electrised,  they  stand  out  and  repel  each  other,  with  a  force 
indicated  by  the  distance  at  which  they  are  separated.  The  distance  is  a 
rough  measurer  of  the  intensity  or  energy  of  the  charge. 

By  attaching  the  pith-balls  to  an  insulated  cylinder  (Fig.  2iq),  round  which  a 
riband  is  wound  up  close,  and  conveying  a  charge  from  the  electrical  machine, 
they  repel  each  other  for  some  time,  and  remain  in  that  state  in  dry  and  moder¬ 
ately  warm  air.  If,  however,  the  flap  or  riband  of  silk  is  unwound  by  the  glass 
handle,  the  electricity  is  spread  over  a  larger  surface,  the  intensity  of  the  ori¬ 
ginal  charge  is  diminished,  and  this  is  shown  by  the  pith-balls  falling  together, 
and  again  returning  to  their  original  distance,  or  nearly  so,  when  the  glass  is 
again  wound  up. 

This  experiment  is  quite  in  accordance  with  the  laws  of  Coulomb,  already 
explained  at  page  228.  Instead  of  the  proof  plane,  a  “carrier  ball,”  as  Fara¬ 
day  termed  it,  may  be  used  ;  this  is  made  of  some  nicely  turned  light  wood, 
covered  with  gold  paper,  and  supported  by  a  silk  thread,  well  dried,  and  satu¬ 
rated  with  shellac.  The  latter  is  easily  dissolved  in  methylated  spirit,  by 
digestion  in  the  cold  for  a  day  or  so.  Of  course,  warming  the  spirit  by  putting 
the  bottle  on  a  piece  of  wood  standing  on  the  hob  of  a  grate  will  accelerate 
the  solution;  but  care  must  be  taken  to  avoid  the  chance  of  its  taking  fire. 
Most  of  the  above  experiments  were  devised  by  Faraday;  but  it  is  easily 
shown  that  the  principle  of  distribution  and  the  proof  that  electricity  resides 


262 


ELECTRICITY. 


Fig.  210. —  The  Cylinder  charged ,  and  the  flap  unwound. 

on  the  surfaces  of  metallic  electrified  bodies  was  well  known  and  shown  by 
Cavallo  in  his  book  published  in  1777.  The  experiment  quoted  is  called 

The  Electric  Well. 

“  Place  upon  an  electric  stool  a  metal  quart  mug,  or  some  other  conduct¬ 
ing  body  nearly  of  the  same  form  and  dimension ;  then  tie  a  short  cork-ball 
electrometer  at  the  end  of  a  silk  thread  proceeding  from  the  ceiling  of  the 
room,  or  from  any  other  proper  support,  so  that  the  electroscope  may  be  sus¬ 
pended  within  the  mug,  and  no  part  of  it  may  be  above  the  mouth;  this  done, 
electrify  the  mug  by  giving  it  a  spark  with  an  excited  electric,  or  otherwise, 
and  you  will  see  that  the  electroscope,  whilst  it  remains  in  that  insulated 
situation,  even  if  it  be  made  to  touch  the  sides  of  the  mug,  is  not  attracted  by 
it,  nor  does  it  acquire  any  electricity  ;  but  if,  whilst  it  stands  suspended 
within  the  mug,. a  conductor,  standing  out  of  the  mug ,  be  made  to  communi¬ 
cate  with  or  only  presented  to  it,  then  the  electroscope  acquires  an  electricity 
contrary  to  that  of  the  mug,  and  a  quantity  of  it  which  is  proportionable  to 
the  body  with  which  it  has  been  made  to  communicate ;  and  it  is  then  imme¬ 
diately  attracted  by  the  mug.  Cavallo  explains  the  cause  in  his  own  quaint 
language,  and  his  theory  is  in  accordance  with  that  taught  in  these  days,  only 
the  technical  names  are  changed  ;  thus,  in  modern  style,  the  fact  would  be 
explained  by  stating  that  “  polarity  cannot  be  set  up  when  opposing  actions 
are  at  work  in  different  directions,  as  in  the  inside  of  an  insulated  metallic 
vessel.”  Cavallo  says,  “  The  reason  why,  in  this  experiment,  the  electroscope 
contracts  no  electricity  whilst  suspended  entirely  within  the  cavity  of  the  mug 
is  because  the  electricity  of  the  mug  acts  upon  the  electroscope  on  all  sides , 
and  this  has  no  opportunity  of  parting  with  its  fluid  when  the  mug  is  electri¬ 
fied  positively,  nor  of  receiving  any  when  the  mug  is  electrified  negatively. 
But,  as  soon  as  any  conductor  communicates  with  it,  the  electroscope  becomes 
immediately  possessed  of  the  electricity  contrary  to  that  of  the  mug;  for,  if 
the  mug  be  electrified  positively,  the  fluid  belonging  to  the  electroscope  will 
be  repelled  to  that  body  which  communicates  with  it,  and  which,  being  out 


THE  ELECTRIC  WELL. 


263 


of  the  mug,  cannot  be  affected  by  its  electricity ;  and  if  the  mug  is  electrified 
negatively,  it  will  attract  the  fluid  of  the  electroscope,  which  actually  receives 
an  additional  quantity  of  it  from  that  conducting  body  with  which  it  com¬ 
municates. 


Fig.  21 1. — Cavallo's  Electric  Well. 

A,  quart  mug  insulated,  and  containing  the  electroscope  inside;  b,  the  threads  raised  above  the 
edge  of  the  vessel,  or,  still  better,  touched  with  an  insulated  brass  rod  extending  into  the  air. 
tn  a,  opposing  feces,  +  and  +,  oppose  in  different  directions  In  b,  polarity  can  be  set  up ;  because  the 
inside  is  +,  the  elect,  oscope  — ,  and  the  extremity  of  the  rod  in  the  air  +. 


“  The  electroscope,  therefore,  becoming  always  possessed  of  a  contrary  elec¬ 
tricity,  must  necessarily  be  attracted. 

“  If,  by  raising  the  silk  thread  a  little,  part  of  the  electroscope,  i.e.,  of  its  linen 
threads,  are  lifted  just  above  the  mouth  of  the  mug,  the  balls  will  be  immedi¬ 
ately  attracted ;  for  then,  by  the  action  of  the  electricity  of  the  mug,  it  will 
acquire  a  contrary  electricity  by  giving  to  or  receiving  the  electric  fluid  from 
the  air  abov  e  the  cavity  of  the  mug. 

“  It  has  been  supposed  by  some  that  the  electroscope  in  the  above  experi¬ 
ment  (or  any  other  small  insulated  body),  hanging  in  the  cavity  of  an  electrified 
vessel,  or  the  like,  is  not  attracted  by  the  sides  of  the  vessel  because  the  attrac¬ 
tion  of  electricity,  being  as  the  squares  of  the  distances  inversely ,  cannot  aftect 
the  electroscope  one  way  more  than  another;  it  being  demonstrable  that  if  to 
every  point  of  a  spherical  concave  surface  equal  centripetal  forces  are  directed, 
decreasing  as  the  squares  of  the  distances  from  those  points,  a  small  body 
situated  anywhere  within  that  surface  would  remain  there  without  being  at¬ 
tracted  one  way  more  than  another.*  But  to  this  it  may  be  replied  that  the 
demonstration  of  the  above-mentioned  proposition,  if  it  is  applicable  to  sphe¬ 
rical  or  cylindrical  concave  surfaces,  cannot,  however,  be  applied  to  every  kind 
of  irregular  cavities,  with  which,  if  they  exceed  not  a  certain  size,  the  above 
experiment  succeeds  as  well  as  with  the  cylindrical  cavity  of  the  mug.” 

Cavallo  proceeds  to  give  what  he  considers  to  be  the  proper  theory,  which 
in  the  main  is  right ;  but,  as  before  observed,  the  explanation  is  simplified  by 
stating  that,  as  polarity  cannot  be  set  up  inside  a  vessel,  so  a  charge  cannot 
be  maintained. 


*  Newton’*  “  Principia,”  Book  I  ,  prop.  Ixx. 


ELECTRICITY. 


264 


ELECTRICAL  INDUCTION. 

In  studying  the  phenomena  of  light  and  heat,  it  will  be  necessarily  observed 
that  these  forces  have  a  radiant  power.  A  heated  body  may  be  brought  towards 
another  which  is  not  heated,  and  impart  to  it  a  certain  amount  of  its  warmth  ; 
the  latter  gains  what  the  former  loses  :  the  vibratory  power  set  up  in  the  heated 
body  is  supposed  to  be  conveyed  by  the  undulations  of  the  ether  to  the  body 
which  is  not  heated,  and  setting  up  therein  similar  vibrations ;  the  result  is 
that  heat  is  produced  in  a  cold  substance  by  the  approach  of  a  heated  body, 
which  loses  its  vibrating  energy  in  warming  the  other. 

Loss  of  power,  independent  of  any  conducting  power  of  damp  air,  curious 
to  say,  is  not  observed  when  an  electrified  body  is  gradually  brought  towards 
another  which  is  not  electrified  ;  and  yet  the  electrical  quiescence  of  the  latter 
is  disturbed,  and  may  give  rise  to  large  quantities  of  electricity,  as  in  Holtz’s 
electrical  machine  (Fig.  202) ;  the  effect  thus  obtained  is  called  “  induced  elec¬ 
tricity.” 

The  fact  is  well  shown  by  using  a  cylindrical  conductor,  the  two  halves  of 
which  can  be  separated  with  their  respective  insulating  glass  columns.  On 
the  underside  of  the  conductor  small  rings  or  hooks  may  be  inserted  for  the 
convenience  of  attaching  pairs  of  gilt  pith-balls,  which  should  be  as  light  as 
possible. 


Fig.  212. 

a,  the  electrified  ball  approached  to  th  *  conductor,  b  c,  made  in  two  halves  to  separate  at  d;  each  half 
to  have  one  suspended  pith-ball  at  d,  so  that,  when  joined  together,  they  form  a  pair  of  balls  as  in  the 
ordinary  electroscope  ;  also  each  to  have  a  pair  at  the  extremities  b  and  c. 

Dii  ectly  the  charged  ball  A  has  approached  sufficiently  near  to  the  conductor 
B  C,  the  pith-balls  show  by  their  mutual  repulsion  that  its  electrical  quiescence 
is  distui bed,  and  that,  in  fact,  if  the  ball  has  been  charged  with  positive  or 
-f-  electricity,  it  will  cause  negative  or  —  electricity  to  become  apparent  at 
B,  whilst  positive  or  +  electricity  will  be  found  at  C.  The  pith-balls  hanging 
at  D  will  hardly  be  disturbed,  if  at  all,  showing  that  there  is  a  neutral  point, 
like  the  centre  of  a  bar  magnet,  where  the  forces  are  balanced.  When  the 
cistuibmg  cause  A  is  removed,  the  separated  electricities  rush  together  again, 
the  electrical  equilibrium  of  the  cylinder  is  restored,  and  the  pith-balls  no 
longer  repel  each  other. 


ELECTRICAL  INDUCTION. 


265 


No  advantage,  therefore,  so  far  as  the  production  of  a  permanent  charge  of 
electricity,  has  been  obtained  in  the  above  experiment,  which,  it  must  be  re¬ 
membered,  is  performed  with  a  conductor  of  electricity.  If,  however,  the  expe¬ 
riment  is  repeated,  and,  whilst  the  conductor  is  under  induction  from  the  ball 
A,  the  two  halves  are  separated,  then  it  will  be  found  that  each  half  is  per¬ 
manently  electrified. 


A,  the  electrified  ball ;  b,  the  half  of  the  cylinder,  separated  from  the  other,  and  showing  a  charge  of 
negative  or — electricity;  c,  the  other  haif,  showing  positive  or  +  electricity  ;  d,  the  single  twl  Is,  sus¬ 
pended  from  r  and  c,  attract  each  other,  as  they  repiesent  the  opposite  electricities,  +  and  — . 


The  separation  of  the  halves  of  the  conductor  whilst  under  induction  has 
prevented  the  opposite  forces  reuniting;  the  pith-balls  remain  deflected  on 
each  half,  and  the  single  balls,  suspended  at  the  place  where  the  two  halves 
are  separated,  incline  towards  each  other,  because  dissimilar  electricitiesattract. 
The  equality  of  the  electrical  disturbance  is  again  beautifully  shown  by  bring¬ 
ing  the  halves  together,  when  the  electrical  excitation  set  up  entirely  ceases,  as 
the  two  opposite  forces  exactly  neutralize  each  other. 

The  experiment  may  be  once  more  repeated,  and  the  two  halves  separated 
whilst  under  induction.  If  a  stick  of  excited  wax  is  approached  to  the  half 
of  the  cylinder  marked  B,  minus,  the  pith-balls  are  deflected  still  further  from 
each  other;  but  when  the  same  stick  of  excited  sealing-wax  is  brought  towards 
C,  or  plus  electricity,  the  balls  drop  down. 

In  the  first  case,  the  increased  deflection  shows  that  the  electricity  on  B  is 
negative,  because  the  wax  is  negative,  and  exalts  the  previous  charge.  In  the 
second,  the  diminished  deflection  and  falling  down  of  the  balls  show  that  th* 
electricity  on  C  is  positive,  as  it  is  neutralized  for  the  time  being  by  the  in¬ 
fluence  of  the  negatively  electrified  wax. 

Two  electroscopes,  one  placed  in  connexion  with  each  half  of  the  conductor, 
may  be  substituted  for  the  pith-balls,  and  are,  perhaps,  more  certain  and 
truthful  in  their  indications ;  moreover,  they  are  more  delicate,  and  would  show 
a  smaller  amount  of  electrical  disturbance. 

These  experiments  demonstrate  that,  in  conductors ,  polarity,  i.e.,  the  sepa¬ 
ration  of  the  electricities,  the  production  of  opposite  properties  in  opposite  di¬ 
rection,  may  be  set  up  by  induction,  but  is  not  maintained;  and  this  is,  in  fact, 
as  contended  by  Faraday,  the  essential  difference  between  conductors  and  non¬ 
conductors  :  in  the  former  polarity  is  not  maintained  ;  in  the  latter,  as  we  shall 


266 


ELECTRICITY. 


now  see.  polarity,  being  set  up,  is  maintained,  or  it  would  be  impossible  to 
charge  a  Leyden  jar. 

When  a  plate  of  glass  is  held  against  the  ball  attached  to  the  prime  con¬ 
ductor  of  an  electrical  machine,  and  a  pith-ball,  suspended  on  a  glass  sup¬ 
port,  is  approached  towards  it,  the  ball  is  energetically  attracted  towards  the 
glass;  and  yet  the  latter,  being  called  a  non-conductor,  ought  not  to  have  per¬ 
mitted  the  electricity  to  have  apparently  travelled,  like  heat,  through  its  sub¬ 
stance. 


Fig.  214. 

a,  one  side  of  the  glass  plate,  which  may  be  one  foot  square,  and  is  held  against  the  ball  of  the  elec¬ 
trified  conductor ;  b,  the  ball  suspended  on  the  glass  stand,  and  attracted  to  the  other  side  of  the  glass  plate. 


The  electricity  does  not  travel  through  the  glass  plate,  but,  like  the  brass 
conductor  (Fig.  212),  is  thrown  into  an  electro-polar  state,  the  one  side  touch¬ 
ing  the  conductor  being  positive,  and  the  other  side,  to  which  the  pith-ball  is 
attracted,  being  negative ;  a  very  slight  charge  is  thus  conferred  upon  the  glass 
plate,  which  will  not  rise  higher  until  one  side  is  put  in  conducting  communi¬ 
cation  with  the  ground.  The  small  charge,  however,  is  retained  when  the 
glass  is  removed,  and  thus  the  polarity  is  shown  to  be  maintained  by  non-con¬ 
ductors,  constituting  the  essential  difference  between  them  and  conductors  of 
electricity. 

The  sheet  of  glass  cannot  be  charged  nropcrly  unless  both  surfaces  are 


ELECTRICAL  INDUCTION. 


267 


coated  with  tinfoil,  within,  say,  2  in.  of  the  outer  edge.  On  a  sheet  of  glass 
1  ft.  square,  the  tinfoil  will  be  8  in.  square.  If  this  plate  is  supported  on 
an  insulating  stand,  by  being  placed  in  the  cleft  or  groove  of  a  piece  of 
mahogany  fitted  on  the  top  of  a  glass  rod,  fixed  in  a  proper  foot,  the  charge, 
as  before  stated,  is  very  slight,  because  the  force  called  positive  electricity 
applied  to  one  side  of  the  plate,  which  may  polarize  the  particles  of  the  glass, 
is  opposed  by  the  positive  electricity  resident  on  the  other  side  of  the  glass, 
and  a  balance  is  arrived  at — a  dead  lock  ;  the  particles  cannot  increase  their 
charge,  because  the  order  is  broken,  and  instead  of  the  continuity  being 
represented  by  Fig.  215,  where  +  is  at  one  end  and  —  at  the  other,  the  regu- 


FlG.  215. 


larity  is  destroyed  by  the  last  particle  being  +  instead  of  — ,  as  shown  at 
Fig.  216  ;  and  the  molecules  are  now  +  at  one  end  and  -f  at  the  other,  and 
must  therefore  oppose  (and  thwart,  as  it  were)  each  other. 


Fig.  216. 


The  difficulty  is,  however,  overcome  by  connecting  one  side  of  the  plate 
with  the  earth,  when  the  order  shown  in  Fig.  215  is  restored,  and  the  -f  elec¬ 
tricity  is  said  to  escape  to  the  ground,  which  latter,  in  its  turn,  represents  a 
vast  series  of  particles  all  polarized  ad  infinitum ,  but  decreasing  in  intensity 
as  the  distance  from  the  disturbing  source  is  increased,  according  to  the  law 
already  explained  at  page  228. 

Faraday  insisted  that  electrical  induction  was  an  action  of  contiguous  par¬ 
ticles,  whether  it  took  place  through  a  metal,  or  glass,  or  air ;  he  opposed  the 
“  emission  ”  theory  of  electricity,  as  others  had  done  before  with  respect  to 
the  emissive  theories  of  light  and  heat. 

Formerly  it  was  supposed  that  electricity  travelled  through  air  without 
affecting  the  particles  of  the  air;  it  was  imagined  to  be  a  subtle  form  of  matter 
of  its  own  kind.  Faraday  laboured  to  prove  that  every  particle  of  air  becomes 
polar,  and  takes  part  in  the  propagation  of  the  force,  just  as  the  particles  of 
the  glass  become  polar  when  charged  with  electricity. 

A  thin  leaf  of  gold  may  be  on  one  side  and  —  on  the  other,  so  long  as 
it  is  subjected  to  the  inductive  action  of  an  electrified  body  brought  near  it ; 


268 


ELECTRICITY. 


that  which  occurs  in  a  large  conductor,  as  shown  in  Fig.  212,  may  occur, 
microscopically,  as  it  were,  in  a  gold  leaf. 

If  once  the  student  grasps  the  idea  of  the  polarity  of  each  minute  and  con¬ 
tiguous  particle,  the  difficulties  of  Faraday’s  inductive  theory  vanish.  It  is 
well,  here,  to  dwell  on  the  condition  of  the  surfaces  of  a  glass  plate  whilst 
under  induction,  and  receiving  a  charge  of  electricity.  The  late  Professor 
Daniell’s  diagrams  are  very  excellent.* 


Fig.  217. — Dante  IPs  Diagram , 

Explaining  the  coruliron  of  the  surfaces  of  an  insulated  and  non-insulated  plate  of  glass, 

coated  with  tinfoil. 


“  Upon  the  molecular  hypothesis  of  induction,  No.  1  may  represent  a  plate 
of  glass  with  its  metallic  coatings,  a  b  and  c  d,  in  its  neutral  state.  In  No.  2, 
we  suppose  the  same  plate,  with  its  metallic  coating,  a  b,  in  contact  with  the 
charged  conductor  of  an  electrical  machine.  Its  other  coatings  we  also 
suppose  to  be  insulated  ;  and,  as  we  know,  the  plate  cannot  be  charged.  The 
coating  a  b ,  however,  being  positive  or  +,  not  only  will  the  particles  of  the 
glass  be  thrown  into  a  polar  state,  but  the  coating  c  d  will  also  be  polar,  -f-  - — , 
by  induction  to  surrounding  objects  ;  but  the  charge  will  not  rise  to  any 
degree  of  intensity,  because  the  electricity  of  the  latter  cannot  be  carried 
off,  or  diffuse  itself  upon  the  earth,  but  will  react  upon  the  glass.  But  if  we 
uninsulate  this  coating,  then  will  No.  3  represent  the  high  state  of  tension 
(charge)  which  the  forces  will  assume  under  the  inductive  process,  when  a 
high  charge  of  4-  electricity  upon  a  b  will  sustain  an  equal  charge  of  —  elec¬ 
tricity  upon  d  c  by  the  polar  arrangement  of  the  particles  of  the  interposed 
dielectric  (glass). 

“In  the  above  diagrams  the  unshaded  circle  represents  the  particles  of  glass 
in  a  state  of  electrical  quiescence ;  the  shaded  circles  represent  polarity,  the 
shaded  half  being  supposed  to  be  (plus),  the  unshaded  half  —  (minus) 
electricity.” 

\Y  hen  explaining  the  cause  of  electricity  residing  on  the  surface  of  an  insu¬ 
lated  conductor,  it  was  stated  that  the  interior  of  the  vessel  (Fig.  21 1)  was  not 
found  to  give  the  slightest  charge  to  the  proof  plane,  because  polarity  could 
not  be  set  up  properly  in  consequence  of  opposing  forces  in  different  directions: 
we  may  trace  out  the  latter  in  the  next  diagram  (Fig.  218).  Suppose  a  set  of 
molecules  in  a  polar  state  starting  from  A  are  met  by  another  column  of 
particies  in  the  opposite  direction  B,  which  virtually  undo  all  that  might  have 


*  Darnell’s  “  Introduction  to  Chemical  Philosophy  ’ 


ELECTRIC  A  L  IND  UCTION. 


269 


A 

-< - WL. 


been  done  by  A.  The  polar  state  cannot  be  set  up  in  the  carrier-ball,  or,  in 
fact,  in  the  particles  of  air  contained  in  the  vessel  under  examination  by  the 
carrier-ball  or  proof  plane. 

The  same  reasoning  applies  to  all  sets  of  molecules  coming  in  the  direction 
C  as  opposed  to  c,  D  as  opposed  to  D,  E  as  opposed  to  E. 

The  nomenclature  of  the  phenomena  of 
induced  electricity  is  thus  expressed  by  Fa¬ 
raday  : 

1.  The  excited  body,  glass  or  wax,  is  called 
the  indue  trie  or  inductive  body. 

2.  The  effect  of  the  inductric  on  a  distant 
body,  and  where  no  loss  of  electricity  is  sus¬ 
tained,  as  by  contact,  is  called  induction. 

3.  The  electricity  thus  obtained  is  called 
induced  electricity. 

4.  The  body  subjected  to  the  action  of  the 
inductric  is  called  the  inducteous  body. 

5.  The  medium,  such  as  air,  through 
which  the  electric  may  act  upon  the  induc¬ 
teous  body  is  termed  the  dielectric  (Sia, 
through,  and  TyAe/arpov,  electricity).  A  di¬ 
electric  may  be  solid,  fluid,  or  gaseous. 

When  the  above  principles  are  once  com¬ 
prehended,  it  is  easy  to  conceive  that  even' 
kind  of  electrical  attraction  must  be  pre¬ 
ceded  by  induction ;  to  demonstrate  this 
fact,  Harris  attached  a  gold  leaf  to  a  disc  of 
gilt  paper,  neatly  fixed  on  a  filament  of  shel¬ 
lac,  and  suspended  by  a  silk  thread.  The 
disc  may  be  attached  to  one  end  of  a  well- 
dried  straw  suspended  by  a  thread;  a  little 
bit  of  tinfoil  on  the  other  end  will  balance 


Fig.  219.— 
Harris's 
strafing 


Sir  William  Snow 
Experiment  demon - 
that  A  t tract ion  is 
preceded  by  Induction. 

A,  the  suspend  d  disc,  with  the  gold  leaf 
attached,  and  repelled  when  b,  the  elec¬ 
trified  disc,  is  approached  towards  it. 


270 


ELECTRICITY. 


the  gilt  disc.  Directly  another  disc  electrified  is  brought  towards  the  sus¬ 
pended  disc,  the  little  gold  leaf  on  the  other  side  stands  out  and  is  repelled, 
showing  distinctly  that  the  opposite  kind  of  electricity  to  that  which  is  the 
disturbing  cause  must  be  eliminated,  or  the  gold  leaf  would  not  move  until 
the  suspended  disc  touched  the  electrified  disc. 

At  page  21 1,  whilst  explaining  the  construction  of  the  electroscope,  it  was 
stated  that  the  instrument  could  be  made  more  delicate  by  the  introduction 
of  a  sinmle  arrangement,  through  which  inductive  action  is  brought  to  bear 
upon  the  cap,  and  through  that  to  the  gold  leaves.  The  part  attached  to  the 
electroscope-stand  is  called  the  condenser ,  and  assists  in  increasing  any  minute 
evolution  of  electricity  that  would  otherwise  be  insufficient  to  overcome  the 
weight  of  the  gold  leaves,  and  cause  them  to  repel  each  other. 


Fig.  220. —  The  Electrical  Condenser. 


* 


a,  plate  supported  on  glass  stem;  b,  plate  on  a  conductirg  stem,  jointed  at  bottom  so  as  to  move  to  any 

position  c. 


It  (Fig.  220)  consists  of  two  circular  brass  plates,  one  supported  by  a  glass 
insulating  stem,  and  the  other  resting  upon  a  conducting  stem  jointed  at  the 
bottom.  When  the  plate  on  the  insulated  stem  is  connected  by  means  of  a 
wire  with  the  cap  of  the  electroscope,  which  may  be  very  feebly  excited,  as  with 
the  pressure  of  Iceland  spar,  on  the  removal  of  the  uninsulated  plate,  the  gold 
leaves  of  the  electroscope  indicate  the  minute  electrical  disturbance. 

It  is  evident  that  between  the  two  plates  there  must  be  a  dielectric  air,  the 
particles  of  which  we  have  already  seen  are  capable  of  assuming  the  electro- 
polar  state. 

The  electricity  from  the  tourmaline  on  the  cap  of  the  electroscope  has 
charged  the  insulated  plate  A,  Fig.  220;  this  throws  the  intervening  air  into 
a  polar  state,  so  that  the  air  is  in  the  same  condition  as  the  glass  plate  with 
its  coatings  of  tinfoil,  the  latter  being  represented  in  this  apparatus  by  the  two 
brass  plates.  If  both  plates  were  insulated,  there  would  be  opposing  forces,  as 
shown  at  p.  239;  but  one,  plate  B,  is  connected  with  the  earth.  At  first,  and 
whilst  the  plates  are  near  each  other,  the  electricity  is  said  to  be  disguised. 
All  this  time,  if  the  electricity  on  the  cap  of  the  electroscope  is  positive  (  +  ), 
it  has,  by  induction  through  the  film  of  air,  thrown  the  second  plate  into  the 
opposite  condition,  negative  or  — . 

The  two  electricities  on  the  two  plates  are,  as  it  were,  engaged  to  each  other; 
the  desire  to  unite,  or  their  tendency  towards  one  another,  is  simply  arrested 
by  the  intervening  air,  and  this  for  the  time  disguises  the  electrical  energy 
which  really  exists;  but  when  the  second  plate  is  removed,  and  the  two  elec¬ 
tricities  are  separated,  then  it  is  found  that  the  feeble  original  charge  has  been 


ELECTRICAL  INDUCTION. 


271 


exalted ;  for,  as  the  feeble  charge  from  the  cap,  connected  with  the  insulated 
brass  plate,  acted  on  the  other  uninsulated  brass  plate,  the  latter,  by  con¬ 
nection  with  the  earth,  like  the  outside  of  a  Leyden  jar,  reacts  upon 
the  insulated  plate  ;  so  that,  when  the  two  are  separated,  a  greater  elec¬ 
trical  effect  is  perceptible.  By  the  repeated  application  of  the  pressed  Iceland 
spar,  and  the  withdrawal  and  return  of  the  plate  B  to  A,  the  charge  is  virtually  in¬ 
creased  or  condensed  on  A.  The  closer  the  two  plates  can  be  brought  together, 
the  better  the  effect;  but,  as  the  particles  of  air  are  soon  broken  through  by 
a  disruptive  discharge  in  the  shape  of  a  spark,  and  particularly  so  if  the  air  is 
at  all  humid,  it  is  found  better,  as  in  Volta’s  condenser,  to  use  a  thin  plate  of 
some  non-conducting  material,  such  as  shellac,  instead  of  air.  The  disguise 
of  the  two  electricities  is  the  more  complete  when  the  metallic  discs  are  brought 
very  close  to  each  other,  because  the  attraction  of  the  two  electricities  becomes 
stronger  as  the  distance  is  diminished.  The  inductive  power  of  the  electrified 
plate  must  be  increased,  and  the  reactionary  force  of  the  second  plate,  con¬ 
nected  with  the  earth,  also  rises  to  a  more  exalted  state. 


Fig.  221. —  The  Gold-Leaf  Condenser 

Is  so  called  because  it  is  adapted  to  a  gold-leaf  electroscope.  The  nicety  of 
manipulation  required  in  order  to  use  the  instrument  properly  is  described  by 
M.  de  la  Rive,  in  his  “Treatise  on  Electricity,”  translated  by  Mr.  Charles  V. 
Walker : 

It  is  composed  of  two  metal  plates,  nicely  adjusted,  of  not  less  than  6  in. 
nor  more  than  1  ft.  in  diameter.  On  of  these  plates  is  screwed  on  the  exterior 
extension  of  the  metal  stem  of  the  electroscope  by  which  the  gold  leaves  are 
supported,  and  has  a  wire  and  ball  attached  to  it,  A ;  the  other,  B,  is  provided 
with  an  insulating  handle,  C,  fixed  vertically  at  its  centre,  and  is  placed  upon 
the  former  so  as  exactly  to  cover  it. 


ELECTRICITY. 


272 


“  The  two  plates  have  been  coated  on  their  surfaces  in  contact  with  several 
layers ,  successively  applied,  of  a  very  liquid  varnish,  formed  of  a  solution  of 
shellac  in  alcohol.  This  varnish,  in  drying,  forms  a  pellicle  whose  thickness 
does  not  exceed  i-25oth  part  of  an  inch,  but  which  is  sufficient  to  prevent  the 
recomposition  of  the  electricities  when  they  are  not  very  strong. 

“The  plates  are  thus  almost  in  contact,  and  the  disguise  of  the  electricity 
is  as  complete  as  possible  ;  and  the  condensing  power  of  this  apparatus  is  very 
considerable;  but  it  can  only  support  very  feeble  charges,  which,  indeed,  are  all 
it  is  intended  to  receive,  it  is  important  that  the  two  plates  be  fitted  to  each 
other  as  accurately  as  possible,  and,  consequently,  that  their  surfaces  be  very 
even.  For  this  reason  there  is  a  limit  to  the  size  of  these  surfaces  that  cannot 
possibly  be  exceeded,  because  their  construction  would  become  too  difficult, 
in  consequence  of  the  conditions  we  have  pointed  out.  The  manipulation  also 
would  be  very  troublesome ;  for  it  is  essential  that  we  should  be  able  to  raise 
the  upper  plate  easily,  and  should  take  care  to  raise  it  perpendicularly,  with¬ 
out  exercising  any  friction  against  the  other,  which  of  itself  would  be  a  source 
of  electricity,  and  would  consequently  interfere  with  the  results. 

“  This  reservation  being  once  made,  it  is  advantageous  to  have  the  largest 
possible  surface,  because  the  quantity  of  electricity  accumulated  is  propor¬ 
tional  to  this  surface. 

“  Experiment  has  demonstrated  that  we  cannot  exceed  a  foot  in  diameter, 
without  falling  into  the  inconveniences  that  we  have  just  pointed  out.  The 
plates  are  generally  of  brass,  and,  if  possible,  of  gilt  brass,  so  as  to  be  pro¬ 
tected  against  the  chemical  action  of  the  moist  air,  and  of  the  vapours  and 
liquids  with  which  they  may  have  occasion  to  come  in  contact. 

“  Electrical  signs  are  sometimes  found  on  separating  the  two  plates,  even 
although  there  may  be  no  electrical  source  in  communication  with  either  of 
them.  This  error  is  due  to  a  small  quantity  of  electricity  arising  from  preced¬ 
ing  experiments,  which  has  penetrated  into  the  layers  of  varnish,  and  which 
is  not  got  rid  of  without  some  difficulty. 

“  In  order  to  remove  it,  we  must  place  a  very  thin  sheet  of  tinfoil  between  the 
two  discs,  and  leave  it  there  until  we  have  satisfied  ourselves  that,  after  having 
been  placed  in  immediate  contact  with  each  other,  the  plates  liberate  no 
trace  of  electricity  by  the  mere  fact  of  their  separation.  It  is  essential  always 
to  determine  this  absence  of  spontaneous  electrical  signs  before  making  an 
experiment. 

“  F or  greater  convenience,  the  source  of  electricity  is  generally  placed  in  com¬ 
munication  with  the  upper  plate  of  the  condenser  B,  which  is  termed  the  col¬ 
lector ;  and  the  lower  plate,  or  its  connected  brass  ball,  is  touched  with  the 

finger. 

“  When  the  two  plates  are  separated,  it  is  the  electricity  of  the  lower  plate, 
now  become  free,  that  affects  the  electroscope  ;  but  we  must  not  lose  sight 
of  the  fact  of  its  being  of  a  contrary  nature  to  that  of  the  upper  one,  and,  con¬ 
sequently,  to  that  of  the  source  subjected  to  experiment. 

“  Before  beginning  a  second  experiment,  we  must  not  forget  to  discharge  both 
the  plates  by  touching  them  with  the  fingers  ;  and  generally  we  must  never 
leave  them  charged,  especially  when  they  are  in  contact,  because  the  electri¬ 
city  that  they  retain  penetrates  into  the  layers  of  varnish,  from  which,  as  we 
have  seen,  it  is  a  very  difficult  matter  to  expel  it. 

“  By  the  assistance  of  this  instrument  Volta  succeeded  in  showing  that  a  plate 
of  zinc,  when  held  in  the  hand  and  put  into  contact  with  the  upper  plate, 


THE  ELECTROPHORUS. 


273 


charged  it  with  negative  electricity — an  experiment  that  was  the  origin  of  the 
voltaic  pile.  When  this  experiment  is  made,  care  must  be  taken  that  the 
zinc  plate  be  well  cleansed,  especially  in  the  points  where  it  touches  the  disc. 

“  In  like  manner,  we  can  charge  the  plate  with  positive  electricity  by  inter¬ 
posing  between  the  plate  and  the  zinc  plate,  which  is  still  held  in  the  hand,  a 
disc  of  cloth  or  paper  slightly  moistened  with  salt  water.  In  each  case  we 
must  not  neglect  to  touch  the  lower  plate  with  one  of  the  hands,  whilst  the  zinc 
plate  is  held  by  the  other  in  contact  with  the  upper  plate.  The  experiments 
that  we  have  just  quoted,  and  the  other  delicate  experiments  in  which  the  con¬ 
denser  is  used,  require  the  air  of  the  room  in  which  the  operation  is  carried  on 
to  be  as  dry  as  possible,  or  at  least  the  electroscope  and  all  the  pieces  of  w  hich 
it  is  constructed  to  be  well  protected  from  moisture.  With  this  view,  the  whole 
is  covered  with  a  glass  cage,  in  the  interior  of  which  chloride  of  calcium  is 
placed,  in  order  to  produce  the  dryness.” 

Space  does  not  permit  us  to  describe  Peclet’s  instrument,  which  is  still 
more  sensitive,  but  requires  precautions  to  be  taken  in  its  use  that  almost 
negative  its  other  valuable  qualities. 

Professor  G.  Carey  Foster,  F.R.S.,  in  his  valuable  contribution  to  the  Hand¬ 
book  of  the  Special  Loan  Collection  of  Scientihc  Apparatus,  exhibited  in 
1876 at  the  South  Kensington  Museum, speaking  of  “  Electrical  Accumulators 
and  Condensers,”  gives  the  following  philosophical  epitome  of  their  action : 

‘‘  Insulated  conductors  are  needed  for  the  accumulation  of  electricity.  When 
a  conductor,  originally  unelectrified,  is  charged  with  electricity,  its  ‘  electrical 
potential,’ or  degree  of  electrification  (positive  or  negative),  rises  in  direct  pro¬ 
portion  to  the  quantity  of  electricity  that  is  given  to  it.  The  consequence  of 
this  is  that  the  magnitude  of  the  charge  which  can  be  imparted  to  a  given  con¬ 
ductor  is  limited  in  two  different  ways.  In  the  first  p  ace,  there  is  always  a 
practical  (if  not  a  theoretical)  limit  to  the  electrical  potential  which  can  be 
produced  by  the  electrical  machine,  or  other  source  of  electricity,  that  is  em¬ 
ployed  to  charge  the  conductor ;  and  when  the  conductor  has  received  sufficient 
electricity  to  make  its  potential  the  same  as  that  of  the  source,  it  cannot  receive 
any  more.  Secondly,  as  the  potential  of  the  conductor  rises,  its  tendency  to 
impait  electricity  toother  bodies  increases,  and  hence,  if  more  and  more  elec¬ 
tricity  is  continually  supplied  to  it,  the  leakage  consequent  on  the  imperfectly 
insulating  character  of  the  supports,  or  due  to  discharge  through  the  surround¬ 
ing  air,  becomes  after  a  time  equal  to  the  supply,  and  then  the  charge  cannot 
any  longer  increase.  The  quantity  of  electricity  which  an  insulated  conductor 
can  receive  without  having  its  potential  raised  beyond  a  given  limit,  depends 
partly  on  the  extent  and  form  of  its  surface,  and  partly  on  the  position  and 
size  of  other  conductors  in  its  neighbourhood.  The  effect  of  all  these  condi¬ 
tions  is  expressed  by  the  term  ‘ ca parity’ — the  capacity  of  a  conductor  being 
the  quantity  of  electricity  that  is  required  to  change  its  electric  potential  by 
unity.  Hence,  in  general  terms,  the  quantity  0/  electricity  in  a  conductor = 
its  electrical  potential  X  by  its  electrical  capacity. 

*•  It  follows  that  when  a  conductor  has  been  charged  up  to  the  attainable  limit 
of  potential,  the  amount  of  the  charge  can  be  increased  only  by  increasing  its 
capacity — or,  in  other  words,  the  ratio  of  the  quantity  to  the  potential  of  the 
charge.  The  most  effectual  way  of  doing  this  is  to  place  another  conductor 
near  the  one  that  is  to  be  charged,  and  to  give  a  charge  of  the  opposite  kind 
to  that  of  the  latter.  This  is  done  in  the  instruments  known  as  ‘Electrical 
Condensers  and  Accumulators,’  of  which  the  Leyden  jar  is  the  most  familial 

IS 


274 


ELECTRICITY. 


example.  In  this  apparatus  the  conductor  to  be  charged  is  a  sheet  of  tinfoil 
pasted  on  glass,  a  second  piece  o!  tinfoil  being  pasted  opposite  to  it  on  the 
other  side  of  the  glass.  To  charge  the  first  sheet,  say  positively,  it  is  con¬ 
nected  with  the  prime  conductor  of  an  electrical  machine,  and  the  second 
sheet  of  tinfoil  is  connected  (either  directly  or  through  the  earth)  with  the 
rubber  of  the  machine  ;  or  if  any  other  source  of  electricity  is  used,  the  two 
sheets  of  tinfoil  — or  ‘  coatings,’  as  they  are  usually  called — are  connected  with 
the  parts  which  correspond  with  the  conductor  and  the  rubber  respectively. 
The  negative  electrification  of  the  second  coating  then  diminishes  the  positive 
potential  due  to  the  positive  charge  of  the  first  coating,  and  vice  versa;  so 
that  when  the  full  difference  of  potential  which  the  motion  employed  is  capable 
of  producing  has  been  established  between  the  ccatings,  the  quantity  of  elec¬ 
tricity  accumulated  in  each  of  them  is  many  times  as  great  as  that  which  it 
would  receive  in  the  absence  of  the  other. 

“  When  the  limit  of  the  charge  which  can  be  given  to  a  conductor  is  deter¬ 
mined,  not  by  want  of  perfect  insulation,  but  by  the  low  potential  of  the  source 
from  which  it  is  electrified,  the  same  method  of  increasing  the  quantity  of 
electricity  received  by  it  can  be  employed  ;  and  by  removing  the  second  and 
oppositely-charged  conductor,  after  the  conductor  to  be  charged  has  been  dis¬ 
connected  from  the  source,  the  potential  of  the  latter  may  be  raised  so  as 
greatly  to  exceed  that  of  the  source.  Apparatus  with  a  movable  second  con¬ 
ductor  arranged  for  use  in  this  way  are  c&\\q&  ‘  electrical  condensers The 
condenser  appears  to  have  been  first  described  by  Volta  in  1782. 

“  It  will  be  seen  from  what  is  said  above  that  ‘‘quantity  of  electricity,  capa¬ 
city ,  and  difference  of  potential  are  so  related,  that  if  in  a  given  case  two  of 
the  three  are  known,  the  third  is  at  once  determined.  Consequently  the  instru¬ 
ments  required  for  measuring  these  quantities  cannot  be  separated  from  each 
other. 

“  Among  the  most  important  may  be  mentioned  ‘  absolute  standards  of 
capacity’ —that  is,  insulated  conductors  whose  capacity  is  known  from  their 
dimensions  :  the  simplest  is  a  metallic  sphere  at  a  great  distance  from  any 
other  conductors  ;  relative  standards  of  capacity,  or  accumulators  whose 
capacity  has  been  determined  in  terms  of  a  known  absolute  standard  ;  accumu¬ 
lators ;  or  condensers,  whose  capacity  can  be  varied  at  will,  and  by  known 
amounts.  Examples  of  these  are  afforded  by  Sir  William  Thompson’s 
‘  Platymeter ,’  and  various  adjustable  accumulators  formed  by  the  combina¬ 
tion  of  two  or  more  separate  accumulators.  Other  instruments  required  in 
connection  with  them  axe  electrometers  for  absolute  and  relative  measurements 
of  differences  of  potential,  and  standards  of  difference  of  potential,  such  as  the 
standard  element  of  Mr.  Latimer  Clark. 

“  Connected  with  the  measurement  of  capacity  is  the  study  of  the  condition 
of  an  insulating  medium  which  separates  two  oppositely  electrified  surfaces. 

“  It  was  first  shown  by  Faraday  (1837)  that  the  capacity  of  an  accumulator 
depends  not  merely  upon  the  size  and  conformation  of  the  conducting  sur¬ 
faces,  but  also  on  a  property  of  the  insulating  medium  between  them,  which 
he  called  its  ‘  Specific  inductive  Capacity.’  This  property  has  since  been  in¬ 
vestigated  by  various  experimenters,  and  notably  by  Boltzmann  ” 

Within  the  last  few  months  it  has  been  shown  by  Kerr  of  Glasgow,  that 
the  property  of  optical  double  refraction  is  developed  in  insulating  solids  and 
liquids,  when  a  difference  of  electrical  potential  is  maintained  between  j 
opposite  surfaces. 


THE  ELECTROPHORUS. 


* 75 


Another  important  matter  connected  with  the  properties  of  insulating 
media,  under  these  circumstances,  is  the  difference  of  potential  required  to 
make  a  discharge  of  electricity  take  place  through  a  layer  of  given  thickness. 
This  has  been  investigated  as  yet  chiefly  by  Riess,  Rijke,  and  Sir  William 
Thompson. 

The  phenomena  accompanying  the  discharge  of  accumulated  electricity, 
and  the  effects  due  to  it  belong  strictly  to  the  subject  of  electro-dynamics. 
The  following  may  be  mentioned  as  some  of  the  chief  points  that  have  been 
investigated  in  connection  with  the  discharge  :  the  appearance  presented  by 
it  in  air  or  in  other  gaseous  media  at  various  pressures,  when  viewed  either 
with  the  naked  eye  or  through  the  spectroscope  ;  the  duration  of  the  electric 
spark ;  its  heating  action  ;  its  oscillatory  character ;  and  its  mechanical  effects. 

By  many  writers,  especially  on  the  Continent,  this  term  is  restricted  to  the 
part  of  the  subject  which  deals  with  the  mutual  force  acting  between  con¬ 
ductors  traversed  by  electric  currents ;  it  is  used  by  Professor  Foster  to  include 
the  whole  of  the  branch  of  electrical  science  which  deals  with  the  effects  of 
electricity  in  motion. 

If  the  condenser  cannot  be  understood,  the  youthful  student  is  supplied  with 
fresh  ideas,  which  will  help  him  to  do  so,  in  the  old-fashioned  and  most  useful 
instrument,  called  the 

ELECTROPHORUS  (rjkeKTpov,  electricity ;  <popos,  carrying). 


Fig.  222. —  The  Electrophorus. 

A  B,  the  tin  dish,  with  the  sides  sloping  inwards,  so  that  the  composition  cannot  fall  out;  c  C,  the  upper 
metallic  plate  and  glass  handle,  d  ;  e  e,  two  spots  of  sealing- wax,  dropped  and  united  on  to  the 
lower  side  of  the  metallic  plate,  to  keep  it  opposed  to,  but  not  touching,  the  resinous  plate. 

This  instrument  is  spoken  of  by  Cavallo  as  “a  machine  for  exhibiting  per¬ 
petual  electricity  though  he  explains  afterwards  that,  being  only  an  excited 
electric,  it  must  gradually  lose  its  power  like  all  other  excited  electrics,  but 
being  flat  it  is  not  exposed  to  currents  of  air  which  may  circulate  around  a 
stick  of  sealing-wax,  and  carry  off  the  charge  more  quickly. 

To  make  an  electrophorus,  a  circular  tin,  with  a  rim  £  in.  deep,  may  be  pro¬ 
vided,  about  i  ft.  in  diameter,  and  into  this,  whilst  warm,  should  be  poured  a 
mixture  of  two  parts  of  shellac  and  one  part  of  Venice  turpentine,  after  they 
are  carefully  melted  and  well  incorporated  together.  When  cold,  the  surface 

18—  2 


276 


ELECTRICITY. 


has  a  bright  polish,  and  is,  of  course,  remarkably  smooth ;  indeed,  care  should 
be  taken  not  to  scratch  it.  The  second  part  of  the  apparatus — for  it  consists 
only  of  two  parts — is  the  circular  flat  plate,  10  in.  in  diameter,  made  of  tin,  or 
gilt  copper,  or  cardboard-  covered  with  tinfoil,  in  the  centre  of  which  is  a  glass 
rod  so  fixed  that  it  will  lift  the  metallic  plate. 

The  instrument  is  charged  by  gently  rubbing  or  striking  the  resinous  plate 
with  a  cat’s  skin  or  a  warm  piece  of  flannel,  and,  like  the  charged  pane  of 
glass,  described  at  page  238,  the  thinner  the  resinous  plate  can  be  cast,  the  better, 
as  after  being  rubbed,  and  always  supposing  the  tin  dish  is  in  conducting  com¬ 
munication  with  the  earth,  it  acquires  a  charge  like  the  Leyden  jar,  to  be 
described  presently.  The  electro-polar  plate  having  been  set  up  in  the  resinous 
plate,  the  metallic  plate  with  the  glass  handle  (which,  in  common  with  all  the 
glass  supports  of  electrical  apparatus,  should  be  varnished  with  shellac  var¬ 
nish)  is  brought  down  upon  the  excited  resinous  plate ;  no  direct  transfer  of 
electricity  takes  place  except  when  the  plate  happens  to  touch  the  excited  wax, 
and  this  is  prevented,  in  a  great  measure,  by  the  two  little  studs  of  sealing- 
wax,  E  E,  already  spoken  of  in  Fig.  222. 

When  the  plate  is  in  position,  and  held  by  the  glass  handle,  the  two  elec¬ 
tricities,  positive  and  negative,  naturally  resident  in  the  metal,  separate,  as 
already  described  in  the  explanation  of  the  phenomena  of  induction,  at  page 
237 ;  because  induction  may  not  only  take  place  in  a  long  conductor,  but  on 
the  opposite  sides  of  a  tin,  copper,  or  other  metallic  plate. 

If  the  plate  is  now  removed  and  examined,  it  is  not  found  to  have  acquired 
any  charge  of  electricity  ;  conductors  do  not  retain polarity ;  and  the  two  forces, 
separated  whilst  the  metallic  plate  was  in  the  neighbourhood  of  the  excited 
resinous  plate,  come  together  again,  as  already  described  fully  at  page  236. 

The  metal  plate  is  again  laid  upon  the  lower  excited  resinous  plate,  and 
now,  if  touched  by  the  finger  just  the  moment  before  it  is  raised  by  the  glass 
handle — for  the  act  of  touching  and  raising  should  be  almost  simultaneous, 
and  is  soon  learnt  with  a  little  practice — then,  on  applying  the  knuckle  to  the 
edge  of  the  metallic  plate  or  to  the  brass  ball,  a  spark  immediately  passes; 
and  thus,  by  continually  touching,  raising,  and  applying  the  top  metallic  plate 
by  its  glass  handle  to  a  small  Leyden  jar,  the  latter  is  speedily  charged. 

The  rationale  of  the  necessity  for  touching  is  easily  explained.  When  the 
plate  is  under  induction,  the  lower  side  facing  the  negatively  electrified 
resinous  plate  is  positive,  and  the  upper  side  negative;  on  touching  the  plate, 
positive  electricity  passes  to  the  negative,  and  the  upper  surface  receives  a 
charge  in  excess  of  its  natural  quantity,  and,  instead  of  the  two  sides  being 
represented  by  +,  plus,  and  — ,  minus,  the  plate,  when  removed,  is  found  to 

be  -) - K  Here  is  an  excess  of  electricity,  which  passes  to  the  knuckle  in 

the  form  of  a  spark,  and  again  restores  the  equilibrium  to  +  and 

It  is  in  this  way  that  the  metallic  plate  can  be  charged  any  number  of  times 
by  alternately  touching  and  raising,  and  the  resinous  plate  loses  no  electrical 
power  whatever. 

Holtz’s  electrical  machine,  described  at  p.  226,  is  another  and  very  notable 
instance  of  the  same  kind. 

If  the  resinous  plate  in  its  tin  dish,  before  being  rubbed,  is  placed  on  an 
insulating  stand,  so  as  to  be  well  insulated,  and  is  then  rubbed,  care  being 
taken  not  to  touch  the  metallic  dish,  it  acquires  little  or  no  charge.  The  under 
side  of  the  resinous  plate  must  be  in  conducting  communication  with  the 
ground,  like  the  glass  plate  with  the  tinfoil  coatings,  described  at  p.  239. 


THE  ELECTROPHORUS. 


277 


When  the  whole  apparatus,  previously  excited  and  ready  for  use,  is  placed  on 
the  insulating  stand,  and  the  metallic  plate  raised,  it  acquires  so  slight  a  charge 
that  it  will  not  give  a  spark,  and  would  only  affect  an  electroscope,  which, 
Cavallo  says,  “  shows  that  the  electricity  of  this  resinous  plate  will  not  be  con¬ 
spicuous  on  one  side  of  it,  if  the  opposite  side  is  not  at  liberty  to  part  with  or 
acquire  more  of  the  electric  fluid.” 

The  original  electrophorus  invented  by  Volta  was  a  circular  glass  plate, 
covered  with  a  composition  made  of  equal  parts  of  shellac,  rosin,  and  sulphur; 
and  these  plates,  no  doubt,  from  their  thinness,  would  answer  the  purpose  re¬ 
markably  well. 

Cavallo,  who  is  always  so  thoroughly  practical  in  his  electrical  experiments, 


F IG.  223. — Electrophorus,  made  of  Glass,  and  covered  with  Sealing-wax. 

says  that  he  made  one  of  a  glass  plate,  and  no  more  than  6  in.  in  diameter: 
when  once  excited,  it  could  charge  a  coated  Leyden  phial  several  times  suc¬ 
cessively,  so  strong  as  to  pierce  a  hole  through  a  card  with  the  discharge. 
Sometimes  the  metal  plate,  when  separated  from  it,  was  so  strongly  electrified 
that  it  darted  strong  flashes  to  the  table  upon  which  the  electric  plate  was  laid, 
and  even  into  the  air,  besides  causing  the  sensation  of  the  spider  s  web  upon 
the  face  brought  near  it,  like  an  electric  strongly  excited. 

“  The  power  of  some  of  my  plates  ”  (which  he  covered  with  sealing-wax, 
second  quality),  he  says,  “  is  so  strong,  that  sometimes  the  electric  plate  adheres 
to  the  metal,  when  this  is  lifted  up  ;  nor  will  they  separate,  even  if  the  metal 
plate  is  touched  with  the  finger  or  other  conductor.” 

Thus,  with  a  circular  piece  of  window-glass,  covered  with  sealing-wax  melted 
on  to  it,  a  circular  piece  of  wood  or  card  covered  on  both  sides  with  tinfoil, 
and  fixed  by  a  pasteboard  tube  to  a  glass  rod,  a  very  serviceable  and  cheap 
electrical  machine  can  be  made  by  young  people. 

The  Levden  jar  is  nothing  more  than  the  coated  glass  pane  (p.  238)  rolled 
up  or  made  into  a  cylinder. 

It  was  discovered  by  three  philosophers,  who  were  working  together  at 
Leyden,  viz.,  Muschenbroeck,  Allaman,  and  Cuneus.  They  were  attempting 
to  collect  and  store  electricity  in  a  bottle,  containing  some  water,  through  the 
cork  of  which  was  thrust  a  nail,  touching  the  water;  the  first  shock  was  re¬ 
ceived  when  Muschenbroeck,  holding  the  bottle  in  one  hand,  touched  the  nail 
with  the  other  accidentally.  One  smiles,  recollecting  personal  experience  in 


278 


ELECTRICITY. 


these  matters,  to  imagine  the  half-frightened  wonderment  of  the  worthy  sage, 
who  might  have  supposed  that  he  had  invoked  the  demon  or  “genius,”  good 
or  evil,  of  the  bottle. 

Of  course,  everybody  throughout  Europe  was  made  acquainted  with  the 
electric  shock  by  travelling  electricians,  who,  like  the  travelling  “ghost”  show¬ 
men  of  the  present  day,  relieved  Muschenbroeck  of  any  trouble  in  communi¬ 
cating  his  discovery  to  the  world  in  general. 

As  the  water  was  found  to  be  inconvenient,  in  consequence  of  the  vapour 
condensing  in  the  upper  part  of  the  bottle,  and  thus  reducing  the  distance 
between  the  outer  and  inner  surface  of  glass,  so  that  a  small  charge  only  could 
be  obtained,  brass  filings,  fixed  on  with  some  varnish,  were  next  tried;  and 
Cavallo  devotes  more  than  a  page  of  his  “Complete  Treatise  on  Electricity” 


Fig.  224. —  The  Leyden  Jar  and  Discharger. 


to  the  narrative  of  a  grand  explosion  and  smoke  arising  from  the  interior  of 
his  Leyden  bottle,  prepared  with  varnish  and  brass  filings,  in  consequence  of 
the  latter  taking  fire  with  the  electric  spark,  which,  darting  from  point  to 
point  of  the  filings,  set  the  inflammable  mixture  of  air  and  spirit  vapour  from 
the  varnish  on  fire  ;  and  he  adds,  regretfully,  that,  after  it  had  burnt  out,  all 
the  brass  filings  fell  to  the  bottom  of  the  bottle,  because  the  adhesive  quality 
of  the  varnish  was  destroyed  by  fire. 

1  he  older  electricians  sometimes  used  mercury  instead  of  water;  but  this 
was  soon  found  to  be  very  expensive,  and  not  applicable  to  large  jars,  in  con¬ 
sequence  of  the  great  weight  of  the  metal. 

The  principle  of  the  Leyden  jar  being  once  understood,  viz.,  that  the  water 
accidently  used  by  Muschenbroeck  in  his  bottle  was  the  inner  conducting 
coating  that  conveyed  the  electricity  to  all  parts  of  the  interior  surface  of  the 
glass,  and  that  the  undesigned  application  of  the  hands  on  the  outside  served 
for  the  outer  coating,  a  little  more  consideration  brought  electricians  to  the 
use  of  tinfoil,  no  doubt  suggested  by  the  use  of  this  metal  in  the  art  of 
suvering  looking-glasses. 

There  are  no  better  directions  for  coating  and  preparing  Leyden  jars  and 
batteries  than  those  given  by  Cavallo,  who  says,  “  When  glass  plates  or  jars. 


THE  LEYDEN  JAR. 


279 


having  a  sufficiently  large  opening,  are  to  be  coated,  the  best  method  is  to 
coat  them  with  tinfoil  on  both  sides,  which  may  be  fixed  upon  the  glass  with 
varnish,  gum-water,  paste,  beeswax,  &c. ;  but  in  case  the  jars  have  not  an 
aperture  large  enough  to  admit  the  tinfoil,  or  an  instrument  to  adapt  it  to  the 
surface  of  the  glass,  then  brass  filings,  such  as  are  sold  by  the  pin-makers, 
may  be  advantageously  used,  and  they  may  be  stuck  with  gum-water,  bees¬ 
wax,  &c. ;  but  not  with  varnish ,  for  this  is  apt  to  be  set  on  fire  by  the  discharge. 
Care  must  be  taken  that  the  coatings  do  not  come  very  near  the  mouth  of 
the  jar,  for  that  will  cause  the  jar  to  discharge  itself  (now  called  a  spontaneous 
discharge. 

“  If  the  coating  is  about  two  inches  below  the  top,  it  will  in  general  do  very 
well ;  but  there  are  some  kinds  of  glass,  especially  tinged  glass,  that,  when 
coated  and  charged,  have  the  property  of  discharging  themselves  more  easily 
than  others,  even  when  the  coating  is  five  or  six  inches  below  the  edge. 

“  There  is  another  sort  of  glass,  like  that  of  which  Florence  flasks  are  made, 
which,  on  account  of  some  unverified  particles  in  its  substance,  is  not  capable 
of  holding  the  least  charge.  On  these  accounts,  therefore,  whenever  a  great 
number  of  jars  are  to  be  chosen  for  a  large  battery,  it  is  advisable  to  try 
some  of  them  first,  so  that  their  quality  and  power  may  be  ascertained. 

“  If  a  battery  is  required  of  no  very  great  power,  as  containing  about  eight 
or  nine  square  feet  of  coated  glass,  I  should  recom¬ 
mend  to  make  use  of  common  pint  or  half-pint  phials,  fy 

such  as  apothecaries  use.  They  may  be  easily  coated 
with  tinfoil,  sheet  lead,  or  gilt  paper  on  the  outside, 
and  brass  filings  on  the  inside.  They  occupy  a  small 
space,  and,  on  account  of  their  thinness ,  hold  a  very 
good  charge ;  but  when  a  large  battery  is  required, 
then  these  phials  cannot  be  used,  for  they  break  very 
easily,  and  for  that  purpose  cylindrical  glass  jars  of 
about  fifteen  inches  high,  and  four  or  five  inches  in 
diameter,  are  the  most  convenient.” 

It  is  easily  shown,  by  charging  a  Leyden  jar  fitted 
with  shifting  coatings,  made  of  light  tin-work  or  of 
wire  gauze,  that  they  have  nothing  to  do  with  the 
maintenance  of  the  charge;  they  simply  act  as  chan¬ 
nels  for  the  conveyance  of  the  electricity  to  all  parts 
of  the  glass.  It  is  the  polarity  of  the  particles  of  the 
glass,  which  is  kept  up  as  long  as  the  jar  is- charged, 

and  is  only  destroyed  when  the  interior  of  the  jar  is  brought  in  conducting 
communication  with  the  exterior  by  means  of  the  useful  instrument  called  the 
discharger,  already  shown  in  Fig.  224. 

The  Leyden  jar  with  shifting  coatings,  having  been  charged,  is  discharged 
with  a  loud  snapping  noise,  by  bringing  one  ball  of  the  discharger  to  the 
outside,  and  the  other  to  the  ball  coming  from  the  inside. 

The  jar  is  again  charged,  and  the  arm  of  the  discharger  is  used  to  take  out 
the  interior  coating.  Directly  that  is  removed,  the  jar  may  be  lifted  out  of  its 
outer  coating,  and,  if  the  air  of  the  room  is  dry,  may  be  left  some  time  without 
fear  of  its  losing  the  charge.  The  charged  Leyden  jar  would  keep  its  elec¬ 
trical  polarity  still  longer,  if  put  under  a  dry  glass  shade,  as  the  air  around  the 
Leyden  jar  would  then  remain  still,  and  would  thus  retard  the  slow  discharging 
of  a  charged  glass  surface,  when  the  air  of  the  room  is  in  constant  motion,  by 


!»• 

im 

p  - . : 

-:-y>r 

Fig.  225. — Leyden  Jar 
with  shij ting  coatings. 


28o 


ELECTRICITY. 


reason  of  the  warmth  of  the  fire,  or  the  movements  of  persons  about  the  room 
who  are  engaged  in  making  the  experiments. 

After  waiting  a  reasonable  time,  the  jar  may  be  lifted  into  its  outer  coating, 
and  the  inner  one  can  be  quickly  and  dexterously  returned,  by  the  assistance 
of  the  discharger,  to  the  interior;  and  now,  on  applying  the  discharger  as  before, 
a  loud  cracking  and  brilliant  spark  prove  that  the  charge  was  confined  to  the 
particles  of  the  glass. 


A  R 


Fig.  226, 

a,  the  conical  glass  jar;  b,  the  outer  coating;  c,  the  inner  coating;  d,  the  discharger. 

An  insulated  Leyden  jar,  like  the  coated  pane  described  (page  238),  cannot 
sustain  a  charge.  Franklin  soon  discovered  this  fact,  and  hence  the  experi¬ 
ment  is  usually  called  “  Franklin’s  experiment  with  the  Leyden  jar.” 

The  jar  may  be  supported  on  a  stand  with  a  long  glass  support,  which  of 
course  must  be  dry,  and  insulate  perfectly. 

It  should  always  be  remembered  that  a  steady  gentle  warmth  is  far  better 
than  roasting  the  apparatus  before  a  large  fire ;  indeed,  a  great  deal  of  damage 


28i 


THE  LEYDEN  JAR. 


is  done  to  electrical  apparatus  by  foolishly  exposing  to  a  strong  heat  instruments 
which  are  partly  put  together  with  cement :  the  latter  melts,  and  the  symmetry 
and  perfection  of  a  piece  of  apparatus  is  often  entirely  spoilt ;  because  it  requires 
some  experience  to  cement  a  brass  cap  on  to  a  glass  vessel,  and  the  young 
electrician  can  do  little  or  nothing  with  his  apparatus  when  the  cement  is 
melted  and  running  down  the  inside  or  outside  of  it. 


Fig.  227. — Franklin's  Experiment  with  the  Insulated  Jar. 


The  interior  of  the  jar  is  now  connected  with  the  ball  of  the  prime  con¬ 
ductor  of  the  electrical  machine,  and,  after  receiving  some  sparks,  it  will  be 
noticed  that  they  cease  to  pass,  and  that  the  conductor  is  showing,  by  its 
electrical  brushes  and  discharges  through  the  air,  that  there  is  no  charge 
passing  into  the  Leyden  jar. 

When  removed  from  the  conductor,  by  pushing  the  insulating  stand  on  one 
side,  and  tested  with  the  discharger,  little  or  no  spark  is  perceptible.  If, 
however,  the  wire  and  ball  on  which  the  Leyden  jar  stands — usually  inserted 
into  and  made  movable  on  the  top  of  the  insulating  stand — is  now  connected 
by  a  chain  with  the  ground,  the  jar  is  very  quickly  charged,  when  sparks  are 
received  from  the  prime  conductor. 

The  rationale  has  already  been  explained  at  page  240,  but  may  be  repeated 

here. 

When  insulated,  the  positive  electricity  naturally  resident  on  the  outside  of 
the  glass  opposes  any  accumulation  of  positive  electricity  in  the  interior;  the 
chain  of  particles  is  not  continuously  charged  in  the  order  of  plus  and  minus, 
but  is  interrupted  by  plus  coming  in  the  wrong  place;  the  order,  however,  is 
restored  when  the  outside  of  the  jar  is  connected  with  the  ground,  as  the 


282 


ELECTRICITY. 


natural  positive  electricity  finds  a  channel  through  which  it  can  escape,  and 
no  longer  opposes  the  accumulation  of  the  positive  charge  inside  the  jar. 

When  a  number  of  jars  are  insulated  on  glass  stands  and  placed  in  regular 
order,  the  knob  of  the  first  being  connected  with  the  prime  conductor,  the 
knob  of  the  second  to  the  outside  of  the  first,  the  knob  of  the  third  in  con- 


Fig.  228. — Charging  the  Leyden  Jar  by  Cascade. 


tact  with  the  outside  of  the  second,  and  the  outside  of  this  last  connected 
with  the  ground,  the  whole  series  is  charged  by  the  first,  because  the  first 
loses  exactly  the  proportion  of  positive  electricity  which  enters  its  interior; 
this  passes  to  the  second,  which  in  its  turn  loses  the  equivalent  from  the  out¬ 
side,  and  finally  passes  or  flows,  as  it  were,  into  the  third  jar,  the  outside  of 
which  is  connected  with  the  ground.  Thus  the  positive  or  plus  electricity  of 
the  first  jar,  like  a  continuous  cascade,  flows  from  one  jar  to  the  other,  and,  all 
being  charged,  they  cannot  be  discharged  together;  to  effect  this,  the  interior 
of  all  the  jars  must  be  connected  together,  and  the  same  must  be  done  with 
the  exteriors. 


Fig.  229.  The  Jars  turned  round  by  their  Insulating  Glass  Supports. 

a  a,  brass  rod,  laid  on  the  wires  and  knobs  connected  with  the  interior  of  the  jars,  not  by  the  hand,  hut 
wit  1  a  silk  thread;  b  b,  brass  rod,  laid  on  outside  of  jars  with  hand;  c,  dischargei,  bringing  the  ends 
01  two  rods  in  coi  ducting  communication,  and  spark  discharged. 


Each  jar  can  be  turned  round  at  right  angles,  and  a  brass  rod,  with  balls  at 
each  end,  suspended  by  a  silk  thread,  can  be  laid  across  all  the  wires  and 
'nobs  of  the  jars,  and  another  wire  laid  along  the  exterior  of  the  jars  ;  then, 


THE  LEYDEN  JAR. 


283 


if  the  two  extremities  of  the  rods  in  conducting  communication  with  the  out¬ 
sides  and  insides  of  the  jars  are  brought  in  contact  with  the  discharger,  a 
brilliant  spark  and  louder  noise  announces  the  discharge  of  the  series  of  three 
jars  which  had  been  charged  with  electricity  according  to  the  original  method 
discovered  by  Franklin. 

Mr.  I  sham  Baggs  displayed  some  very  brilliant  experiments  at  the  Poly¬ 
technic  with  Leyden  jars,  charged  in  the  manner  already  described  ;  and,  by  a 
particular  mode  of  arranging  them  in  positive  and  negative  series,  a  very  long 
and  brilliant  spark  was  obtained.* 

It  has  been  shown  by  the  Franklin  experiment  that  a  jar  cannot  be  charged 
unless  the  outside  is  placed  in  communication  with  the  ground;  it  has  also 
been  pointed  out  that  Leyden  jars  are  usually  charged  by  passing  the  electri¬ 
city  to  the  interior.  A  Leyden  jar  can,  however,  be  charged  from  the  exterior  ; 
and  the  arrangement  for  this  purpose  is  shown  at  Fig.  230. 


Fig.  230. —  The  Leyden  Jar  charged  from  the  exterior. 

A  brass  disc,  C,  is  screwed  on  the  top  of  the  ball  of  the  large  jar  A,  in 
order  to  carry  the  smaller  one  B.  When  A  is  charged,  B  becomes  polarized, 
but  cannot  accumulate  a  charge  until  the  positive  electricity  from  the  inside  is 
allowed  to  escape ;  this  is  done  by  touching  the  knob  of  B  and  the  outside  of 
A  with  the  two  balls  of  the  ordinary  discharger.  A  flash  takes  place  when  this 
is  done,  and  now  both  A  and  B  are  charged.  The  inner  surface  of  B  is  nega- 


*  •*  Journal  of  the  Royal  Society,”  Jan.  13,  18.48. 


284 


ELECTRICITY. 


tive,  the  inside  of  A  is  positive ;  the  outside  of  A  is  negative,  the  outside  of  B  is 
positive. 

Both  jars  may  be  discharged  by  using  two  dischargers:  one  connects  the 
outside  of  A  with  the  inside  of  B,  thus  bringing  together  the  two  negative  sur¬ 
faces  ;  and  the  other  discharger  by  touching  the  first  one  and  then  being 
advanced  to  the  stage  C,  which  represents  the  positive  electricity,  the  usual 
flash  and  discharge  follow  directly  the  discharger  comes  within  the  striking 
distance. 

A  collection  of  Leyden  jars,  fitted  up  with  wires  and  balls  communicating 
with  each  other,  and  placed  on  a  sheet  of  tinfoil,  so  that  the  exterior  of  the 
jars,  like  the  interior,  may  be  in  conducting  communication,  constitutes  what 
is  termed  a  Leyden  battery.  (Fig.  223.) 


Fig.  231. —  The  Leyden  Battery. 


The  five  large  jars  are  coated  with  tinfoil,  and  the  brass  balls  belonging  to 
each  jar  are  supported  by  a  method  proposed  by  the  Rev.  F.  Lockey,  and 
recommended  because  it  sometimes  occurs  that  a  jar  will  break  during  the 
discharge  of  the  battery,  although  the  electricity  may  pursue  the  path  intended 
for  it.  Jars  are  more  likely  to  break  if  the  wire  to  which  the  ball  is  attached 
is  carried  down  to  the  tinfoil  inside.  Direct  metallic  communication  with  one 
point  of  the  interior  of  the  jar  is  not  so  safe  as  having  four  contacts,  and  this 
is  secured  by  the  bar  of  wood,  covered  with  tinfoil,  and  connected  with  two 
cross-pieces  of  thinner  wood  laths,  also  covered  with  tinfoil,  and  shown  at  A  B, 
Fig.  231.  It  is  evident  that  contact  is  made  at  two  places,  A,  B,  at  the  top, 
and  two  at  the  bottom,  c,  D. 

The  writer  has  in  his  possession  two  very  large  jars,  which  he  coated  with 


EXPERIMENTS. 


285 


tinfoil,  after  first  pasting  a  coating  of  paper,  such  as  paper-hangers  use,  on  the 
jars,  and  allowing  the  paper  to  rise  one  inch  above  the  tinfoil  coatings.  The 
jars  expose  a  surface  of  six  square  feet  of  glass, 
and  have  been  in  use,  without  fracture,  for  the 
last  twenty-five  years,  although  frequently  very 
highly  charged,  to  break  square  pieces  of  maho¬ 
gany,  to  demonstrate  the  mechanical  power  of 
the  electric  discharge.  Young  experimentalists 
would  do  well  to  avoid  these  trying  experiments, 
as  the  electricity  may  prefer  to  break  through  the 
glass,  instead  of  travelling  only  through  the  nbres 
of  the  wood. 

Henley’s  electrometer,  shown  at  H,  Fig.  231, 
should  always  be  inserted  in  one  of  the  balls  of 
the  battery  whilst  it  is  being  charged,  as  it  indi¬ 
cates,  by  the  rise  of  the  arm  carrying  a  light  pith- 
ball,  the  amount  of  charge,  and  when  it  reaches 
90°  the  jars  are  fully  charged. 

It  is  sometimes  convenient  to  keep  a  jar 
charged  for  a  considerable  time,  and  particularly 
if  the  electricity  is  required  for  medical  purposes; 
this  is  done  by  passing  a  glass  tube  through  the 
wooden  cover  of  the  Leyden  jar:  the  tube  is  lined 
half-way  up  from  the  bottom  with  tinfoil,  and 
terminates  at  the  top  with  a  brass  cap ;  to  con¬ 
nect  this  with  the  interior  of  the  ja r,  a  wire  with 
a  loop  at  the  top  passes  through  the  brass  cap, 
and,  after  the  jar  is  charged,  may  be  removed  by 
turning  the  jar  upside  down,  when  it  tumbles 
out ;  or,  better  still,  it  may  be  taken  away  with  a  ^  IG-  232-  77  She  ordinary 
curved  wire  and  ball,  supported  on  a  glass  handle.  Leyden  Jar ,  coated  with 

Tinfoil , 

And  containing  the  glass  tube  a  b,  capped  with  brass  at  a,  and  passing  through  the  wooden  top,  which 

is  usually  cemented  in  and  well  varnished,  c  shows  the  height  to  which  the  tube  is  lined  with  tinfoil  ; 

d  is  the  wire,  with  ring  at  the  top,  removable  by  the  insulated  curved  wire  w\ 


Experiments  with  the  Electrical  Machine,  the  Leyden  Jar, 

and  Leyden  Battery. 

I.  The  charging  and  discharging  of  a  Leyden  jar  is  beautifully  shown 
by  coating  the  inside  and  outside  with  diamond  and  spotted  coatings, 
or  little  bits  of  tinfoil  cut  in  the  form  of  diamonds  or  spots,  and  pasted 
on  so  that  an  interval  of  glass  surface  may  occur  between  each  of 
them.  When  connected  with  the  prime  conductor,  the  jar  presents  a 
brilliant  and  most  pleasing  appearance  during  the  time  it  is  being 
charged,  and  also  at  the  moment  when  the  discharger  is  used  ;  and 
the  jar  so  coated  is  usually  called  a  spangled  jar. 

II.  Similar  spots  or  small  circles  of  tinfoil  pasted  round  a  glass  tube  show 
a  brilliant  spark  between  each  interval  or  space  left  between  the  spots, 
when  held  to  the  prime  conductor,  or  at  the  moment  that  the  charge 
of  a  Leyden  jar  is  sent  through  them.  The  tube  is  usually  capped 
with  brass  at  each  end. 


286 


*  ELECTRICITY. 


Fig.  233. 

A  Spangled  Jar. 


Fig.  234. 

A  Spangled  Tube. 


Fig.  235. 


III.  Narrow  strips  of  tinfoil  are  arranged  in  parallel  lines  on  a  plate  of  glass, 
so  that  a  continuous  conducting  strip,  commencing  with  a  ball  at  the 
top  of  the  glass  and  ending  with  one  at  the  bottom,  is  obtained. 

The  strips  are  then  neatly  cut  out,  so  as  to  leave  a  small  interval 
sufficiently  wide  to  show  the  spark,  and  delineate  in  a  succession  of 
sparks  anv  word,  such  as  the  name  of 


EXPERIMENTS. 


287 


IV.  A  glass  bottle  may  be  coated  inside  and  outside  with  weak  glue  and 
rather  large  brass  tilings  shaken  inside  and  sifted  over  the  glue  out¬ 
side.  Of  course,  one  side  must  be  done  first — viz.,  the  inside ;  and  the 
coating  should  be  carried  about  as  high  as  the  usual  coating  of  tinfoil. 
It  should  terminate  top  and  bottom  with  a  band  of  tinfoil,  and  it  exhibits 
a  very  pretty  effect  when  hung  on  to  the  conductor  of  the  electrical 
machine,  the  outside  being  connected  with  a  wire  or  chain  with  the 
ground.  The  intervals  between  the  filings  give  rise  to  the  most  varied 
and  beautiful  appearances  of  lines  and  forked  electric  sparks ;  and 
as  the  jar  discharges  itself  when  the  accumulation  reaches  a  certain 
point,  measured  by  the  distance  between  the  wire  from  the  inside 
and  the  outside  coatings,  the  effect  is  continuous  as  long  as  the  elec¬ 
trical  machine  is  turned. 

V.  A  little  tow  wrapped  round  one  of  the  balls  of  the  discharger,  and  dipped 
in  alcohol  or  ether,  is  set  on  fire  directly  the  spark  of  the  Leyden  jar 
passes  through  it. 

VI.  A  person  standing  on  a  stool  with  glass  legs,  and  holding  in  one  hand 
the  chain  from  the  prime  conductor  of  an  electrical  machine  in  motion, 
may  set  on  fire  spirit  or  ether  (held  to  him  by  some  one  else)  in  a 
metallic  spoon,  by  merely  allowing  a  spark  to  pass  from  his  finger  to 
the  inside  of  the  edge  of  the  spoon.  The  hair  of  the  person  standing 
on  the  stool,  and  connected  with  the  electrical  machine,  stands  out  in 
a  very  fantastic  manner,  if  the  hair  is  fine,  silky,  and  well  combed  out 
previously. 

VII.  When  a  blunt  wire,  say  §  in.  thick,  and  nicely  rounded  off  at  the  end, 
is  fixed  into  the  conductor  of  an  electrical  machine  (there  are  holes 
drilled  expressly  for  putting  in  wires),  as  the  handle  is  turned,  a  feeling 
like  a  gentle  current  of  air  is  felt,  when  the  face  is  approached  to  it, 
and,  if  the  room  be  darkened,  very  pretty  brush-like  discharges  are 
seen. 


Fig.  237. 

The  brush  discharge  from  a  positnely  electrified  wire  The  reverse-  the  concentration  of  the  same 
brush  mto  a  glow  or  star  when  positive  electricity  is  drawn  towards  the  negative  conductor.  The  one 
is  the  re  e'se  of  the  other. 

If  the  same  blunt  wire  is  placed  in  the  negative  conductor  and  the 
electrical  machine  put  into  rapid  motion,  a  sort  of  glow  or  star  is  seen 
on  the  end  of  the  blunt  wire.  In  the  first  case,  the  positive  electricity 
is  escaping  from  the  wire;  in  the  second,  it  is  going  into  and  towards 
the  wire. 

VI 1 1.  An  egg-shaped  glass  vessel,  provided  with  a  ground-glass  plate,  a  collar 


5  88 


0 


ELECTRICITY. 


of  leather  at  the  top,  and  through  which  a  brass  rod  and  ball  move 
so  as  to  approach  to  or  recede  from  another  ball  fixed  into  the  lower 
cap,  cemented  on  to  the  glass  and  provided  with  £  stop-cock,  is  first, 


Fig.  23S. 

exhausted  of  air  with  the  air-pump.  Directly  it  (Fig.  238)  is  con¬ 
nected  with  the  electrical  machine,  a  beautiful  glow  of  delicate  violet- 
coloured  light  is  seen  to  pass  between  the  balls. 


Fig.  239. 

fX  The  electrical  inclined  plane  (Fig.  239)  is  formed  by  two  inclined  wires 
stretched  between  four  glass  pillars.  When  a  very  light  rod  of  wood, 
covered  with  burnished  gilt  paper,  having  fine  wires  inserted  at  right 


EXPERIMENTS. 


289 


angies,  with  their  ends  all  bent  exactly  alike,  is  placed  on  the  wires 
which  are  connected  with  the  conductor  of  the  electrical  machine,  the 
rod  revolves  by  reason  of  the  reaction  of  the  dispersed  particles  of 
electrified  air  upon  those  which  are  still,  and  it  rolls  up  the  inclined 
plane.  If  the  experiment  is  tried  in  a  darkened  room,  all  the  points 
exhibit  pretty  brushes  of  electric  light. 

X.  If  the  inside  of  a  clean  dry  tumbler  or,  better  still,  a  German  beaker 
glass,  is  held  over  the  brass  rod  and  ball  of  the  conductor,  and,  after 
being  well  electrified,  is  put  down  over  a  number  of  light  pith-balls 


FlG.  240. — The  Etectrical  Dance  of  Puppets. 

placed  on  a  metallic  plate ;  the  latter  are  attracted  and  repelled  in  the 
most  amusing  manner,  and,  if  the  glass  will  take  a  good  charge, 
the  effect  lasts  some  time,  and,  when  apparently  stopped,  may  be  often 
renewed  by  drawing  the  finger  over  various  parts  of  the  outer  surface. 

XI.  Light  pith  figures,  if  well  made  and  balanced,  perform  a  sort  of  dance, 
by  jumping  up  and  down  between  a  flat  brass  plate  connected  with 
the  conductor  and  suspended  opposite  another  plate  connected  with 
the  ground  (Fig.  240).  When  the  shadow  of  the  figure  is  cast  on  a 
disc,  everybody  can  see  the  experiment,  which  then  assumes  gigantic 
proportions. 

XII.  A  bell  (Fig.  241)  may  be  constantly  struck  with  clappers,  so  arranged 
that,  whilst  the  bell  is  insulated  and  electrified,  the  clapper  is  alternately 
attracted  and  repelled.  Or,  if  the  bell  is  placed  in  connection  with 
the  inside  of  a  Leyden  jar  (Fig.  242),  and  the  outside  with  another 
bell,  the  two  being  opposite  to  each  other,  and  having  between  them 
a  suspended  clapper,  the  bells  will  continue  to  ring  until  the  jar  is 
discharged: 

XIII.  A  very  elegant  experiment  devised  by  Lichtenberg,  and  called  after 
him  Lichtenberg  figures,  is  thus  described  by  De  la  Rive: 

“Lichtenberg  figures  make  manifest  without  an  electroscope, and  in 

*  19 


290 


ELECTRICITY. 


a  directly  visible  form,  the  nature  of  the  electricity  with  which  the  inner 
coating  of  a  jar  is  charged.  This  experiment  consists  in  slowly  passing 
over  a  cake  of  resin  (or  flat  plate  of  vulcanite)  the  knob  of  a  Leyden 
jar,  while  the  outer  coating  is  held  in  the  hand:  we  may  even  trace 
figures  with  the  knob. 

“  The  free  electricity  of  the  inner  coating,  which  is  constantly  renewed 
in  proportion  as  it  escapes,  because  the  other  coating  is  held  in  the 
hand,  remains  adhering  to  all  the  points  of  the  cake  which  the  knob 
has  touched. 

“  If,  after  having  thus  traced  out  lines  with  the  knob  of  a  jar  charged 
interiorly  with  positive  electricity,  we  trace  others  beside  them  with 
the  knob  of  another  jar.  charged  with  positive  electricity,  we  may  render 
each  of  them  visible  and  distinct  by  powdering  the  cake  with  a  powder 
lormed  ot  a  mixture  of  sulphur  and  red  lead  that  have  been  rubbed 
together.  We  perceive  that  all  the  particles  of  sulphur  place  them¬ 
selves  on  the  positive  lines,  and  all  those  of  red  lead  upon  the  negative ; 
and  they  remain  adhering  there,  even  when  we  blow  them  or  shake 
the  cake  strongly,  so  as  to  make  the  portion  cf  the  powder  disappear 
which  is  not  upon  the  parts  of  the  surface  that  had  been  touched  by 
the  knob. 

“  The  effect  that  we  have  just  described  arises  from  the  particles  of 
sulphur,  during  their  mutual  trituration,  having  acquired  negative 
electricity,  and  those  of  red  lead  positive,  which  causes  the  former 
to  pass  upon  the  positive  traces,  and  the  latter  upon  the  negative. 
We  also  remark  that  the  sulphur  forms  a  small  tuft  round  each  of  the 
positively  electrified  points,  whilst  on  each  of  the  negative  points  the 
red  lead  leaves  only  a  circular  spot.  This  phenomenon,  establishing, 
as  it  does,  a  very  remarkable  difference  between  the  two  electricities, 
is  due  to  a  more  general  cause. 

“The  property  that  we  have  thus  recognised  in  resin,  of  retaining  both 


ELECTRICAL  DISCHARGERS. 


291 


electricities  adhering  to  its  surface,  is  not  peculiar  to  this  substance 
alone:  all  bodies  that  are  insulators  possess  it  in  a  more  or  less  marked 
degree.  We  have  already  seen  that  it  exists  in  glass,  when  we  elec¬ 
trized  the  interior  of  a  glass  jar,  to  produce  the  dance  of  pith  balls. 
A  Leyden  jar,  the  coatings  of  which  are  movable  (see  Fig.  226),  fur¬ 
nishes  a  further  proof  of  this. 

“  The  jar  is  charged  as  usual ;  then  with  an  insulating  handle  the 
inner  coating  is  lifted  away,  and  afterwards  the  glass  itself  is  lifted 
out:  the  two  coatings,  being  thus  detached,  manifest  no  electrical 
signs.  The  two  electricities  have,  in  fact,  remained  adhering  to  the 
glass,  the  positive  on  the  interior  surface,  and  the  negative  on  the  ex¬ 
terior. 


Fig.  244. — Harris’s  / mfiroved 
Law's  Electrometer. 


“  These  two  electricities  are  recovered  again  by  replacing  the  jar 
within  its  outer  coating,  and  placing  within  it  its  inner  coating;  the 
discharge  takes  place  between  the  two  coatings  as  if  they  had  not  been 
deranged.  The  fact  just  pointed  out  explains  why  a  Leyden  jar  always 
retains  electricity  after  a  first  discharge,  even  when  the  latter  has 
given  rise  to  a  strong  spark.  We  can  obtain  a  second  discharge, 
much  weaker,  it  is  true,  than  the  former,  but  yet  very  sensible,  and 
sometimes,  indeed,  exceedingly  violent,  if  the  jar  is  large,  and  has 
been  strongly  charged. 

“This  second  discharge  arises  from  a  portion  of  the  two  electricities 
having  remained  adhering  to  the  glass  after  the  first  discharge,  not¬ 
withstanding  the  contact  of  all  the  points  of  the  two  surfaces  ol  the 

19 — 2 


29  2 


ELECTRICITY. 


jar  with  the  metal  surfaces  ;  but  the  second  discharge  is  generally 
sufficient  to  make  all  the  remaining  traces  disappear.” 

XIV.  A  very  portable  and  simple  apparatus  for  obtaining  electricity  and 
charging  a  Leyden  phial  was  arranged  by  Mr.  Adams,  an  optician  of 
the  same  date  as  Cavallo.  It  consists  of  a  half-pint  phial,  coated  inside 
with  brass  filings,  and  outside  with  tinfoil,  and  is  charged  by  a  var¬ 
nished  silk  ribbon,  which  is  rubbed  by  being  passed  through  hare-skin 
rubbers  placed,  like  finger-stalls,  on  the  first  and  middle  fingers  of  the 
left  hand.  The  following  directions  are  given  for  the  proper  manipu¬ 
lation  of  the  silk  rubbers : — Place  the  two  finger-caps  of  hare-skin  on 
the  proper  fingers ;  hold  the  phial  at  the  same  time  at  the  edge  of  the 
coating,  on  the  outside,  between  the  thumb  and  first  finger  of  the  left 
hand ;  then  take  the  ribbon  in  your  right  hand,  and  steadily  and  gently 
draw  it  between  the  two  ribbons,  over  the  two  fingers,  taking  care  at 
the  same  time  that  the  brass  ball  of  the  jar  is  kept  nearly  close  to  the 
ribbon  while  it  is  passing  through  the  fingers. 

By  repeating  this  operation  thirteen  or  fourteen  times,  the  electrical 
fire  will  pass  into  the  jar,  which  will  become  charged,  and,  by  placing 
the  discharger  against  it,  you  will  see  a  sensible  spark  pass  from  the 
ball  of  the  jar  to  that  of  the  discharger.  If  the  apparatus  is  dry  and  in 
good  ord  jr,  you  will  hear  the  crackling  of  the  sparks  when  the  ribbon 
is  pass’n;  through  the  fingers,  and  the  phial  will  discharge  at  about 
the  distance  of  half  an  inch  from  the  balls. 

XV.  In  order  to  regulate  the  proper  discharge  of  single  Leyden  jars  and 
batteries,  very  useful  contrivances  have  been  invented. 

The  arrangement  (Fig.  243)  consist  of  a  bent  glass  arm,  which  is 
fixed  to  the  rod  and  ball  passing  to  the  inside  of  the  jar;  the  arm  carries 
a  tube  through  which  a  rod,  with  balls  at  both  ends,  slides.  The  dis¬ 
tance  between  the  two  balls,  one  of  which  represents  the  interior  and 
the  other  the  exterior  of  the  jar,  is  regulated  according  to  the  scale 
graduated  on  the  sliding  rod,  so  that  a  discharging  spark  of  any  re¬ 
quired  length  (confined  within  the  limits  of  the  charged  surface  of 
the  jar)  may  be  obtained.  Sir  W.  Snow  Harris  improved  the  arrange¬ 
ment  of  Lane’s  discharging  electrometer,  by  making  it  an  indepen¬ 
dent  piece  of  apparatus,  that  might  be  adapted  to  one  or  more  jars. 

The  exploding  balls  of  this  instrument  (Fig.  244)  are  supported  be¬ 
tween  a  bent  glass  arm  and  a  vertical  tube  of  brass,  and  may  be  set 
at  any  given  distance  by  means  of  a  graduated  slide.  The  bent  arm 
of  glass  is  attached,  and  is  movable  on  a  stout  glass  cylindrical  rod, 
so  as  to  insulate  the  whole,  if  required,  and  adjust  the  ball  to  be  con¬ 
nected  with  the  inside  of  the  jar  or  battery  to  any  given  height.  These 
and  other  pieces  of  electrical  apparatus  are  made  most  correctly  and 
elegantly  by  a  number  of  firms  of  American  and  foreign  manufac¬ 
turers  ot  philosophical  instruments.  The  American  workers  have 
long  been  celebrated  for  their  electrical  apparatus. 

XVI.  Cuthbertson’s  Balance  Electrometer  is  an  extremely  useful  contri¬ 
vance,  where  large  Leyden  batteries  are  required  to  be  rapidly  and 
uniformly  discharged,  as  at  the  Polytechnic,  where  the  deflagration 
of  metallic  wires  is  displayed.  The  apparatus  consists  of  a  wooden 
stand,  in  which  two  glass  rods  or  supports  are  fixed  :  one  of  the  insu  ¬ 
lating  rods  or  pedestals  supports  a  orass  ball,  which  has  a  little  hook 


ELECTRICAL  DISCHARGERS. 


293 


below  it,  for  the  convenience  of  attaching  the  chain  passing  from  the 
outside  of  the  Leyden  battery ;  the  other  and  higher  glass  pedestal 
supports  a  large  brass  ball,  in  which  is  arranged  a  long  brass  rod, 
supported  on  knife-edges,  and  acting  like  a  balance  ;  above  this,  and 
proceeding  from  the  same  large  brass  ball,  is  another  rod  and  ball, 
placed  so  that  the  ball  of  the  latter  is  exactly  over,  and  almost  touching, 
the  other  and  lower  one,  that  works  on  knife-edges. 


Fig.  245. — Cuthbertson's  Balance  Electrometer. 

A,  B,  glass  supports.  The  hook  of  A  is  connected  by  a  chain  with 
the  outside  of  the  battery.  B  carries  the  large  ball  through  which  the 
balance-rod,  D,  works.  The  sliding  weight,  E,  like  that  of  a  steel 
rod,  enables  the  experimenter  to  adjust  the  balance  perfectly.  H,  the 
upper  and  fixed  wire  and  ball,  which,  when  sufficiently  electrified  by 
contact  with  the  inside  of  the  battery,  by  the  hook  and  chain  at  K, 
repels  the  movable  balance  D,  and,  making  the  circuit  complete 
(as  shown  by  the  dotted  lines)  by  touching  the  brass  ball  on  A,  the 
whole  discharge  of  the  battery  is  sent  through  any  substance. 

With  Cuthbertson’s  compound  universal  discharging  electrometer, 
the  experimenter  may  always  have  notice  when  the  battery  is  nearly 
charged  and  ready,  by  inserting  in  the  upper  ball  a  Henley's  quadrant 
electrometer,  with  graduated  arc.  The  oscillation  of  the  balance, 
when  the  battery  is  almost  ready,  will  likewise  serve  to  warn  the  person 
using  it  that  he  may  expect  the  discharge  to  occur. 

XVII.  In  connection  with  the  Leyden  battery,  a  Cuthbertson  balance  elec' 
trometer  and  Henley’s  universal  discharger  and  press  are  always 
employed  when  a  variety  of  substances  are  to  be  subjected  to  the 
powerful  effects  of  a  large  charged  surface  of  glass.  The  mechani¬ 
cal  arrangements  are  such  that  the  direction  of  the  charge  is  certain 
and  precise. 

The  annexed  figure  (246)  hardly  requires  any  explanation,  as  the 
parts  are  so  simple.  It  consists  of  two  glass  legs  which  support,  by 


ELECTRICITY. 


294 


hinged  joints,  two  brass  rods  and  balls  with  glass  handles  attached. 
The  latter  slides  through  tubes,  and  may  be  caused  to  advance  or 
recede  from  each  other,  or  they  move  right  or  left,  as  the  hinged 
joints  work  in  sockets. 

The  balls  meet  either  on  the  little  table,  in  which  a  piece  of  ivory 
is  inserted,  or  the  little  table  can  be  removed  and  the  press  substituted 
for  it  ;  as,  for  instance,  when  it  is  required  to  show  the  immense 


FlG.  246. — Henley's  Universal  Discharger  and  Press. 

mechanical  force  of  the  electrical  discharge  by  putting  gold  leaf 
between  glass  plates,  and  passing  a  charge  through  them,  which 
shatters  the  glass  to  fragments,  and  frequently  forces  the  gold  leaf 
into  the  body  of  the  glass.  In  this  experiment,  it  is  usual  to  put  the 
glass  plates  in  the  press,  and,  to  prevent  accident  from  the  pieces  of 
glass  flying  about,  it  is  better  to  cover  the  whole  with  a  dry  clean 
duster. 

XVIII.  Unscrew  by  a  turn  or  two  the  balls  attached  to  the  arms  of  the  Hen¬ 
ley  discharger ;  take  some  very  fine  iron  wire,  such  as  is  used  by 
silversmiths  for  making  scratch-brushes,  and  having  twisted  a  little 
in  the  crack  or  opening  left  by  unscrewing  the  balls,  screw  them  up 
again,  when  the  thin  wire  will  be  held  tightly,  and,  the  length  having 
been  adjusted  to  the  power  of  the  Leyden  battery  employed,  the  whole 
is  dispersed  in  minute  white-hot  globules  when  the  electric  charge 
is  sent  through  the  wire. 

XIX.  Place  the  balls  of  the  Henley  discharger  on  the  little  table,  about  one 
inch  apart  ;  put  some  gunpowder  between  them.  When  the  dis¬ 
charge  of  the  Leyden  battery  is  sent  across  and  through  the  gun¬ 
powder,  it  is  not  ignited,  but  every  grain  is  dispersed  and  thrown 
away  by  the  mechanical  violence  of  the  discharge,  which  occurs  so 
rapidly,  that  the  heat  of  the  electric  discharge  does  not  appear  to 
have  time  to  affect  the  gunpowder. 

When  the  great  steam  hydro-electric  machine  was  in  use  at  the 
Polytechnic,  it  was  possible,  by  directing  from  a  point  the  whole  dis¬ 
charge  of  the  mammoth  machine  for  some  minutes  into  a  heap  of  gun 
powder,  to  accumulate  heat  and  set  it  on  fire ;  but  it  was  always  very 
troublesome  to  do,  and  a  great  deal  of  steam  had  to  be  used  to  effect 
this  object.  If,  however,  a  damp  string  formed  part  of  the  conduct¬ 
ing  arrangement,  then  the  powder  fired  almost  instantaneously,  as 


EXPERIMENTS. 


295 


the  damp  string  exercises  a  retarding  action  on  the  velocity  of  the 
current  of  electricity,  and  it  then  appears  to  have  time  to  give  its 
heat  to  the  powder. 

To  fire  gunpowder  by  the  Leyden  jar,  a  little  cardboard  tray  may 
be  placed  on  the  table  of  the  Henley  discharger;  and  in  order  not  to 
spoil  the  polish  of  the  balls,  two  copper  wires  are  thrust  through  the 
sides  of  the  tray  containing  the  powder,  and  the  brass  balls  of  the 
Henley  discharger  connected  with  them.  A  wet  string  may  be  tied  to 
one  rod  and  also  to  an  ordinary  discharger,  the  other  rod  being  con¬ 
nected  by  a  chain  with  the  exterior  of  the  Leyden  jar;  the  ordinary 
discharger  with  the  wet  string  is  made  to  touch  the  knob,  and,  although 
it  sometimes  fails,  the  powder  is  very  generally  ignited  directly  con¬ 
tact  is  made.  To  fire  gunpowder,  a  wet  string  must  form  part  of 
the  circuit.  The  powder  may  be  placed  in  a  closed  case  or  cartridge, 
so  that  it  cannot  be  scattered  by  the  mechanical  violence  of  the  dis¬ 
charge. 

Sturgeon  retards  the  velocity  of  the  discharge  by  placing  the  gun¬ 
powder  in  a  boxwood  cup  which  is  insulated  and  connected  with  the 
outside  of  the  jar.  An  insulated  brass  wire  and  ball  is  placed 
directly  over  the  cup,  and,  directly  contact  is  made  with  this  and  the 
interior  of  the  Leyden  jar  by  the  ordinary  discharger,  the  powder  is 
usually  fired. 

XX.  A  piece  of  mahogany,  about  two  inches  long  and  £  in.  square,  may 
be  split  by  passing  the  discharge  into  and  through  it  by  two  copper 
wires  inserted  about  half  an  inch,  one  at  each  end.  The  softer  the 
wood,  the  safer  the  experiment  so  far  as  the  jars  are  concerned,  and, 
as  already  observed  at  page  255,  this  experiment  must  not  be  pushed 
too  far  by  using  larger  and  thicker  pieces  of  wood. 

XXL  When  a  lighted  composite  candle  is  blown  out  carefully,  there  rises 
from  it  a  column  of  gas  and  smoke,  which  is  inflammable.  If  such  a 
candle  is  placed  on  the  table  of  the  Henley  discharger,  and  the  balls 
adjusted  so  that  the  spark  will  go  through  a  point  just  above  the 
burning  wick,  and  the  whole  connected  with  a  charged  Leyden  jar, 
the  spark  will  relight  the  candle,  if,  simultaneously  with  the  blowing 
out  of  the  flame,  contact  is  dexterously  made  with  the  Leyden  jar. 


XXII.  The  expansion  which  air  undergoes  during  the  passage  of  an  electric 
discharge  through  it  is  shown  by  a  very  nicely  constructed  mortar, 
to  the  mouth  of  which  is  accurately  fitted  a  ball  of  some  light  wood. 


296 


ELECTRICITY. 


When  the  discharge  passes,  the  ball  is  forced  out;  and  if  the  whole 
is  made  of  ivory(Fig.  246),  the  effect  is  very  certain.  The  expansion 
of  the  air  in  this  experiment  will  help  the  student  to  understand  why 
so  much  noise  (thunder)  is  heard,  when  the  electrical  discharge 
takes  place  from  hundreds  of  acres  of  charged  clouds. 

XXI I J.  The  experiment  called  the  “  Shooting  Star  ”  is  extremely  beautiful,  but, 
like  many  other  illustrations,  requires  considerable  pains  to  be  taken  in 
order  to  obtain  a  good  result.  In  the  first  place,  a  long  tube  must  be  pro¬ 
vided  at  least  four  feet  in  length  ;  this  is  properly  capped,  and  provided 
with  a  stopcock  at  one  end  and  a  plain  cap  on  the  other,  which  should 
be  nicely  rounded  off,  and  inside  the  cap  a  small  ball  maybe  screwed. 
The  electrical  machine  being  in  gO“>d  order,  and  the  Leyden  battery, 
of  six  square  feet  of  glass,  warm  and  dry,  one  assistant  may  proceed 
to  charge  it  gradually,  whilst  another  may  be  pumping  the  air  out  of 
the  long  tube.  When  the  electrometer  shows  that  the  battery  is  nearly 
charged,  one  end  of  a  chain  is  attached  to  one  of  the  balls  of  the 
discharger,  and  the  other  end  to  the  top  of  the  long  tube.  The  air- 
pump  or  stopcock  end  of  the  tube  is,  of  course,  in  conducting  com¬ 
munication  with  the  outside  of  the  battery  jars.  The  circuit  is  now 
suddenly  completed,  and  sometimes  a  continuous  flash  through  the 
whole  length  of  the  tube  marks  the  discharge  of  the  battery ;  but  it 
may  occur  that  it  discharges  itself  in  a  brush,  and  that  the  battery 
must  be  recharged,  and  the  experiment  tried  again.  To  insure  per¬ 
fect  success,  the  experiment  should  be  tried  with  a  barometer  attached 
to  a  pump,  and  then  it  will  soon  be  ascertained  what  vacuum  is  the 
best  for  the  experiment.  Success  greatly  depends  on  the  right 
management  of  the  vacuum,  which  must  not  be  a  perfect  one. 

XXIV.  The  velocity  of  electricity,  and  the  consequent  amazing  rapidity  of 
the  spark-discharge,  and  appearance  or  disappearance  of  the  light, 
is  admirably  shown  by  Mr.  Rose’s  photodrome  apparatus  described 
at  p.  85,  Fig.  95. 

The  writer  uses  the  disc  four  feet  in  diameter,  having  a  series  of  black 
balls  painted  on  a  white  ground  ;  when  this  is  rotating  three  hundred 
times  in  a  minute,  and  the  black  balls  have  all  merged  one  into  the 
other,  according  to  the  law  of  persistence  of  vision,  already  explained 
at  p.  84,  they  produce  (instead  of  twelve  distinct  black  balls)  three 
cominuous  rings,  dark  in  the  centre,  and  lighter  towards  the  edges, 
because  there  the  greatest  surface  of  the  white  disc  is  exposed.  The 
disc  should  be  illuminated  with  a  lime  light  and  lens,  and,  directly 
this  is  cut  off,  a  Leyden  jar,  provided  with  a  Lane’s  discharger,  is  per¬ 
mitted  to  discharge  itself  regularly,  by  keeping  the  electrical  machine 
in  motion  ;  all  the  black  balls  now  return,  and  the  disc,  though  going 
round  three  hundred  times  in  a  minute,  appears  frequently  to  stand 
still. 

The  same  fact  is  observed  during  a  storm  at  night,  accompanied 
with  thunder  and  lightning :  all  objects  seen  by  the  light  from  the  elec¬ 
tric  flash  appear  to  stand  still,  although  they  may  be  in  rapid  motion 
at  the  time.  Captains  of  ships  have  frequent  opportunities  of  noticing 
this  :  a  storm  comes  on  suddenly,  and  some,  if  not  all,  the  sails  of  the 
ship  require  to  be  furled ;  the  command  is  given,  up  fly  the  sailors, 
and  the  deck  and  rigging  swarm  with  men  who  are  actively  engaged  ; 


EXPERIMENTS. 


2Q7 


but  if  at  this  moment  the  ship  is  illuminated  with  a  flash  of  lightning, 
every  officer,  every  man,  the  ship  tossing  about,  and  the  waves  of  the 
sea,  all  appear  at  rest,  as  if  they  were  parts  of  a  magnificent  stereo¬ 
scopic  picture. 

The  fact  is,  that  the  light  from  a  flash  of  lightning,  as  proved  by 
Sir  Charles  Wheatstone,  comes  and  goes  in  the  millionth  part  of  a 
second ;  so  that  before  the  wheel,  going  round  three  hundred  times  in 
a  minute,  has  time  to  move,  the  electric  light  has  arrived  and  passed 
away.  The  same  thing  occurs  with  all  other  movements  viewed  with 
the  electric  flash,  and  the  fleetest  racehorse  even,  under  these  circum¬ 
stances,  would  actually  appear  to  be  standing  still. 

XXV.  Many  years  ago,  Sir  Charles  Wheatstone  invented  a  most  ingenious 
arrangement  for  measuring  the  velocity  of  electricity  through  a 
copper  wire,  and  it  was  from  these  experiments  he  deduced  the 
almost  instantaneity  of  the  light  from  the  electric  spark. 

His  apparatus  consisted  of  a  Leyden  jar,  which  was  charged  in 
every  experiment  to  the  same  amount,  and  the  discharge  sent  through 
a  copper  wire  about  half  a  mile  long. 


Fig.  248. 


The  copper  wire  was  insulated  and  interrupted  at  three  points,  viz. 
one,  A  A,  within  a  few  inches  of  the  inner  coating,  one  at  the  middle 
of  the  circuit,  B  B,  and  one  at  the  same  number  of  inches  of  the 
outer  coating.  C  C,  of  the  Leyden  jar  as  the  first  which  was  in  con¬ 
tact  with  the  inner  coating.  A  very  cleverly  arranged  insulated  disc 
(Fig.  248)  contained  the  three  breaks  in  the  circuit,  where  the  spark 
discharges  Took  place  fso  that  when  the  Leyden  jar  was  discharged, 
all  the  sparks  could  be  seen  at  once,  and  were  reflected  in  a  small 


ELECTRICITY. 


298 


revolving  mirror.  If  observed  without  the  mirror,  the  three  sparks 
appeared  to  occur  simultaneously;  but  when  looked  at  in  a  small 
revolving  steel  mirror  through  a  plate  of  glass,  the  sparks,  accord¬ 
ing  to  the  law  of  persistence  of  vision,  become  lines  of  light,  of 
which  two  are  equal,  whilst  the  third,  representing  the  middle  of  the 
circuit,  is  sufficiently  delayed  to  give  a  shorter  line,  and,  as  the 
velocity  of  the  steel  mirror  is  known,  by  a  proper  register,  the  exact 
angular  deviation  of  the  image  of  the  central  spark  is  easily  ob¬ 
tained ;  and  from  these  data  the  retardation  of  the  current  by  the 
long  copper  wire  is  correctly  calculated. 


Fig.  249. — Apparatus ,  made  by  Messrs.  Elliott ,  to  show  the  time  occupied  by 
the  transmission  of  an  Electric  Current  by  reflection. 

8,  the  revolving  mirror. 


The  three  sparks,  when  seen  in  the  revolving  mirror,  appear  as 
three  straight  bright  lines;  and,  if  the  motion  is  very  fast,  the  lines 
assume  the  appearance  A,  Fig.  250,  when  the  mirror  is  rotated  to  the 


c 


i> 


Fig.  250. — Lines  of  Light  reflected  from  Revolving  Mirror. 

right;  but,  if  reversed,  then  they  appear  as  in  B,  Fig.  250:  but  the 
lines  were  nevei  seen  as  at  c  or  n,  Fig.  250,  which  should  have  been 
the  case  according  to  the  Franklinian  theory  of  a  single  fluid.  Thus 


EXPERIMENl'S. 


299 


Wheatstone’s  ingenious  and  beautiful  experiment  supports  most 
powerfully  the  theory  of  the  two  fluids,  which  seem  to  meet  in  the 
centre  of  the  wire,  as  if  they  rushed  with  equal  speed  to  unite  with 
and  neutralize  each  other. 

The  spark  disc  (Fig.  249)  was  placed  10  ft.  away  from  the  re¬ 
volving  mirror,  and  the  summing-up  of  the  experiments  gave  the 
following  conclusions : 

1.  That  electricity  travels,  through  a  copper  wire  arranged  as  in 
the  experiment  described,  faster  than  light  in  its  passage  from  the 
sun. 

2.  That  the  electricities  of  the  two  kinds,  viz.,  that  from  the  interior 
of  the  jar  and  the  other  from  the  exterior,  travel  at  the  same  velo¬ 
city,  and  meet  in  the  middle  of  the  wire. 

3.  That  the  light  from  the  electric  flash  or  spark-discharger  does 
not  last  longer  than  the  millionth  part  of  a  second. 

4.  That  the  delicate  optic  nerve  is  capable  of  appreciating  an 
interval  of  that  duration,  or,  in  other  words,  can  see  objects  which 
are  only  illuminated  for  the  millionth  part  of  a  second. 


Fig.  25 1. — Appearance  of  the  Card  after  sending  the  discharge  through  Silver 

Wire  1-300 th  of  an  inch  thick. 


XXVI.  Very  fine  "old,  silver,  copper,  brass,  and  iron  wires  can  be  obtained 
of  Messrs.  Johnson  and  Matthey,  at  their  assay  office  in  Hatton 
Garden.  About  three  inches  of  either  metallic  wire  is  stretched 
across  a  plain  white  card  by  making  a  small  cut  in  the  card  at  the 
opposite  ends,  and  then  placing  the  wire  in  the  cuts,  which  may 
be  neatly  closed  with  little  slips  of  tinfoil. 

The  card  with  the  wire  is  then  covered  with  another  card,  and 
placed  between  the  boards  of  the  little  press  attached  to  Henley’s 
universal  discharger  (Fig.  245,  p.  264).  When  tightly  screwed  up 
and  the  brass  balls  of  the  discharger  brought  in  contact  with  the 
ends  where  the  tinfoil  marks  the  termination  of  the  two  ends  of 
the  wire,  the  discharge  from  the  Leyden  battery  can  then  be  sent 
through  it  The  result  is  that  the  wire  is  completely  disintegrated, 


300 


ELECTRICITY. 


and  so  perfectly  divided  that  nothing  remains  upon  the  two  cards 
but  certain  curious  marks  (Fig.  251),  which  are  no  doubt  caused  by 
the  finely  divided  metal  being  driven  bodily  into  the  card, — 
although  it  is  usually  ascribed  to  oxidation,  and  this  may  be  the 
case  with  metals  which  unite  easily  with  that  element.  When  a  very 
thin  iron  wire  is  deflagrated  alone  by  passing  the  battery  discharge 
through  a  length  of  nine  or  twelve  inches,  the  effect  is  very  beau¬ 
tiful,  as  it  is  dispersed  in  a  shower  of  red-hot  globules,  which  are 
well  displayed  in  a  darkened  room. 

The  dissipation  of  gold  by  a  powerful  electrical  discharge  can 
also  be  shown  in  a  similar  manner.  The  metal  is  vaporized,  and 
disappears  in  the  form  of  a  red  vapour. 

By  receiving  the  vapour  from  gold  on  a  piece  of  silk,  a  portrait 
or  other  figure  may  be  printed  upon  it.  To  obtain  these  portraits 
a  likeness  of  any  known  personage  is  cut  out  in  a  small  piece  of 
cardboard,  so  that,  if  held  against  the  wall  with  a  candle  behind 
it,  the  shadow  cast  indicates  that  the  portraiture  is  successful ;  the 
portrait-card  is  now  laid  upon  a  sheet  of  gold  leaf  pasted  to  another 
card ;  and,  as  the  electrical  discharge  would  act  unequally  upon 
the  gold  if  merely  conveyed  through  the  brass  balls  of  the  dis¬ 
charger,  it  is  usual  to  paste  a  slip  of  tinfoil  on  the  opposite  edge  of 
the  gold  leaf,  thus  bringing  all  the  gold  at  once  in  conducting 
communicating  with  the  brass  balls. 


Fig.  252. 

a,  card  coveted  with  gold  leaf,  and  edges  piepared  with  tinfoil ;  b,  portrait-card  ;  c,  the  two  cards,  a  and 
b,  in  press,  and  in  contact  with  the  brass  balls  of  the  discharger. 

XXVI I.  With  the  powerful  hydro-electric  machine  at  the  Polytechnic  (p.  273) 
(to  be  hereafter  described)  a  most  beautiful  effect  was  produced  by 
sending  the  discharge  through  a  long  chain  composed  of  beads  of 
glass  and  copper  strung  on  a  stout  silk  cord ;  and  as  the  latter 
was  at  least  forty  feet  in  length,  the  effect  was  very  imposing. 

On  the  smaller  scale  a  piece  of  brass  chain,  hung  in  festoons  on 
a  plate  of  glass  blackened  at  the  back,  affords  a  very  pretty 
experiment,  being  illuminated  throughout  its  entire  length  when 
the  electrical  discharge  is  sent  through  it. 

XXVIII.  To  imitate  and  demonstrate  the  effects  of  discharges  of  natural 
electricity,  or  lightning,  on  buildings,  &c.,  many  ingenious  models, 
such  as  the  gable  end  of  a  house,  a  pyramid,  a  powder-magazine, 


EXPERIMENTS. 


3°i 


a  ship,  or  mast  of  a  ship,  are  made  by  Messrs.  Elliott,  of  the  Strand, 
London. 


Fig.  253. 


All  these  models  act  upon  one  principle,  viz.,  that  as  long  as  the 
conductor  is  continuous  throughout  and  unbroken,  no  harm  or 
damage  occurs  to  the  model;  but  directly  the  conducting  chain  is 
broken,  by  removing  or  altering  the  position  of  some  part  of  the 
conductor,  then  th.  following  results  occur.  In  the  first  place,  the 
charged  cloud  is  represented  by  Sir  William  Snow  Harris’s  thunder¬ 
cloud  needle  (Fig  254),  formed  by  a  brass  horizontal  rod  or  needle 
balanced  and  movable  upon  the  point  of  a  vertical  metallic  rod 
connected  with  the  interior  coating  of  a  large  Leyden  jar. 


Fig.  254. — Harris’s  Thunder-cloud  Needle. 


One  end  is  covered  with  the  finest  cotton  wool :  a  little  good 
gun-cotton  increases  the  effect,  as  it  may  be  so  arranged  that  every 
time  the  flash  occurs  the  cotton  shall  ignite,  and  the  sudden  flash 
with  the  crack  and  light  of  the  spark  is  remarkably  telling.  The 
cotton  is  intended  to  represent  a  cloud  hovering  over  the  chimney 
or  highest  part  of  a  house  or  church-steeple ;  and,  when  the  jar  has 
been  sufficiently  charged,  it  is  attracted,  according  to  the  law  of 
induction,  to  the  nearest  object,  and  the  simulated  cloud  descends 
upon  the  top  of  the  model,  at  the  same  time  discharging  the  jar 


302 


ELECTRICITY. 


through  the  parts  of  the  models.  As  before  stated,  when  the 
lower  portion  of  the  conductor  attached  to  either  of  the  models 
is  connected  with  the  outside  of  the  jar  by  a  chain,  the  Harris’s 
thunder-cloud  needle  being  in  connection  with  the  interior  of  the 
jar,  the  discharge  causes  no  change  in  the  disposition  of  the  parts 
of  the  toy  model;  but  if,  as  in  A,  Fig.  253,  the  little  piece  of 
square  wood  at  B  is  turned  round  at  right  angles,  the  continuity  of 
the  wire  is  broken,  and  it  is  blown  out  when  the  discharge  takes 
place.  The  model  B  maintains  its  erect  position  if  the  conductor 
is  undisturbed ;  but  when  a  little  bit  of  tinfoil  is  removed  from 
D,  it  topples  over  in  the  most  natural  fashion  when  the  miniature 
thunder-cloud  is  discharged  upon  it. 

The  model  E  affords  a  good  bang,  and  the  roof  is  blown  off  when 
the  powder  in  the  tube  F  is  ignited  ;  but  care  must  be  taken  not  to 
use  too  much  gunpowder.  The  writer  well  remembers  helping 
poor  young  Mr.  John  Cooper,  many,  many  years  ago,  at  a  lecture 
delivered  at  the  Southwark  Institute,  and,  being  directed  sotto  voce 
to  give  them  a  “good  one,”  he  attended  too  implicitly  to  his  in¬ 
structions.  Luckily,  this  was  the  concluding  experiment :  the 
powder-house  blew  up  with  astounding  effect ;  but,  unfortunately, 
the  roof  descended  into  the  middle  of  a  large  cylindrical  electrical 
machine,  and  the  result,  of  course,  was  total  annihilation.  The 
audience,  it  is  believed,  thought  it  was  all  part  of  the  experiment, 
and  applauded  in  the  most  cheering  manner;  but  the  glances  ex¬ 
changed  between  the  lecturer  and  his  assistant  were  of  the  most 
desponding  kind,  considering  that  the  large  electrical  machine  had 
only  been  borrowed  for  the  occasion. 

G,  Fig.  253,  is  called  the  “fire-house,”  and  exhibits  the  heat  of 
the  electrical  discharge,  and  its  power  to  set  tire  to  gun-cotton  or 
tow  dipped  in  ether  or  alcohol;  and,  as  it  is  made  of  tin  and 
glazed  with  glass  windows,  the  conflagration  inside  betrays  the 
lamentable  effects  that  might  and  do  occur  when  houses  are  struck 
and  set  on  fire  by  lightning. 

XXIX.  A  lightning  conductor,  if  intended  to  last,  should  be  made  of  copper 
nd,  at  least  half  an  inch — better  three-quarters — in  diameter.  It 
should  be  carried  above  the  highest  chimney-top,  and  be  well 
pointed  and  doubly  gilt ;  the  lower  end  must  be  carried  down  to  the 
clay,  and  must  enter  the  first  stratum  of  earth  known  to  be  always 
damp.  If  the  building  is  a  long  one,  it  is  better  to  have  a  light¬ 
ning  conductor  at  each  end,  as  a  cloud,  in  coming  up  to  a  lightning 
conductor,  is  always  discharged  through  the  shortest  road ;  and  if 
a  chimney-pot  at  the  other  end  of  the  building  rises  as  high  as  the 
lightning  conductor  at  the  other  end,  it  may  divide  the  honours 
and  dangers  of  the  discharge  with  the  conductor,  provided  the 
cloud  arrives  at  the  side  opposite  to  that  where  the  metallic 
safety-rod  is  fixed. 

XXX.  The  hydro-electric  machine  affords  a  magnificent  example  of 
electricity  derived  from  friction,  and  it  continued  for  a  lengthened 
period  to  be  one  of  the  greatest  attractions  at  the  Polytechnic. 
In  the  “Philosophical  Magazine,”  vol.  vii.,  appeared  a  letter  from 
Mr.  (now  Sir  William)  Armstrong,  giving  a  curious  and  most  inte- 


EXPERIMENTS. 


3°3 


Fig.  255. —  The  Hydro-Electric  Machine  at  the  Polytechnic. 

resting  description  of  the  accidental  production  of  the  electric 
spark  by  high-pressure  steam  escaping  through  a  fissure  or  crack 
in  the  cement  by  which  the  safety-valve  ought  to  have  been  fitted 
in  steam-tight  to  the  boiler  of  a  locomotive  standing  at  Sedgehill, 
six  miles  from  Newcastle.  Every  time  the  engine-man  passed 
his  hand  through  the  steam  he  received  an  intense  elect:  ic  spark, 
which  he  spoke  of  as  “fire.”  Mr.  Armstrong  investigated  the 
phenomena,  and,  continuing  a  very  laborious  and  clever  series  of 
experiments,  arrived  by  gradual  steps  to  the  pioduction  ot  a  per¬ 
fect  steam  machine,  in  which  the  particles  of  water,  impelled  bv 
steam,  rubbing  against  the  interior  of  a  series  of  jets  lined  with 
partridge-wood,  produced  effects  which  have  never  been  surpassed 
in  England.  At  that  time  Dr.  Bachoffner  was  the  very  popular 
lecturer  on  Natural  Philosophy  at  the  Polytecl  nic,  and  he  assisted 
at  and  conducted  most  patiently  the  vast  number  ot  experiments 
which  had  to  be  carried  out  before  the  ponderous  machine  was 
considered  ready  to  be  exhibited  to  the  public.  W  ith  Dr.  Bach¬ 
offner  were  of  course  associated  the  contriver,  Mr.  Armstrong,  and 
Mr.  Walker  ;  and  fearful  that  our  readers  may  think  the  writer  too 
prone  to  talk  of  Polytechnic  doings,  he  has  preferred  to  take  Dr. 
Noad’s  account  of  the  machine  as  exhibited  fifteen  years  ago  at 
that  Institution: 


3°4 


ELECTRICITY. 


“  Shortly  after  these  experiments  were  made,  the  directors  of  the  Polytechnic 
Institution  determined  on  constructing  a  machine,  on  a  large  scale,  for  the 
purpose  of  producing  electricity  by  the  escape  of  steam;  and  under  the  super¬ 
intendance  of  Mr.  Armstrong,  assisted  by  Dr.  Bachoffner,  the  ‘  Hydro- 
Electric  Machine’  was  finished,  and  placed  in  the  theatre  of  the  Institution, 
where  by  its  extraordinary  power  it  soon  excited  the  astonishment  of  all  who 
beheld  it.  The  machine  consists  of  a  cylindrical-shaped  boiler,  similar  in 
form  to  a  steam-engine  boiler,  constructed  of  iron  plate  ^  in.  thick;  its  extreme 
length  is  7  ft.  6  in.,  one  foot  of  which  being  occupied  by  the  smoke-chamber 
makes  the  actual  length  of  the  boiler  only  6  ft.  6  in. ;  its  diameter  is  3  ft.  6  in. 
The  furnace  and  ash-hole  are  both  within  the  boiler.  When  it  is  required 
entirely  to  exclude  the  light,  a  metal  screen  is  readily  placed  over  these.  By 
the  side  of  the  door  is  the  water-gauge  and  feed-valve.  On  the  top  of  the 
boiler,  and  running  nearly  its  entire  length,  are  forty-six  bent  iron  tubes, 
terminating  in  jets  having  peculiar-shaped  apertures,  and  formed  of  partridge- 
wood,  which  experience  has  shown  Mr.  Armstrong  to  be  the  best  for  the  pur¬ 
pose  ;  from  these  the  steam  issues.  The  tubes  spring  from  one  common  pipe, 
which  is  divided  in  the  middle,  and  communicates  with  the  boiler  by  two 
elbows.  By  this  contrivance  the  steam  is  admitted  either  to  the  whole  or  part 
of  the  tubes,  the  steam  being  shut  off  or  admitted  by  raising  or  lowering  the 
two  lever  handles  placed  in  the  front  of  the  boiler.  Between  the  two  elbows 
is  placed  the  safety-valve  for  regulating  the  pressure,  and  outside  them,  on 
one  side,  is  a  cap  covering  a  jet  employed  for  illustrating  a  certain  mechanical 
action  of  a  jet  of  steam,  and  on  the  other  a  loaded  valve  for  liberating  the 
steam  when  approaching  its  maximum  degree  of  pressure.  At  the  further 
extremity  of  the  boiler  is  the  funnel-pipe  or  chimney,  so  contrived  that,  by  the 
aid  of  pulleys  and  a  balance- weight,  the  upper  part  can  be  raised  and  made 
to  slide  into  itself  (similar  to  a  telescope),  so  as  to  leave  the  boiler  entirely 
insulated.  To  prevent  as  much  as  possible  the  radiation  of  heat,  the  boiler 
is  cased  in  wood,  and  the  whole  is  supported  on  six  stout  glass  legs,  3!  in. 
diameter  and  3  ft.  long.  In  front  of  the  jets,  and  covering  the  flue  for  con¬ 
veying  away  the  steam,  is  placed  a  long  zinc  box,  in  which  are  fixed  four  rows 
of  metallic  points,  for  the  purpose  of  collecting  the  electricity  from  the  ejected 
vapour,  and  thus  preventing  its  returning  to  restore  the  equilibrium  of  the 
boiler.  The  box  is  so  contrived,  that  it  can  be  drawn  out  or  in,  so  as  to  bring 
the  points  nearer  or  further  from  the  jets  of  steam  :  the  mouth  or  opening  can 
also  be  rendered  wider  or  narrower.  By  these  contrivances  the  power  and 
intensity  of  the  spark  is  greatly  modified.  A  ball-and-socket  joint,  furnished 
with  a  long  conducting-rod,  has  been  added  to  the  machine,  so  that  by  its  aid 
the  electricity  can  be  readily  conveyed  to  the  different  pieces  of  apparatus 
used  to  exhibit  various  phenomena.  The  pressure  at  which  the  machine  is 
usually  worked  is  60  lbs.  on  the  square  inch. 

“  As  it  is  now  fully  established  that  the  electricity  of  the  hydro-electric 
machine  is  occasioned  by  the  friction  of  the  particles  of  water,  the  latter  may 
be  regarded  as  the  glass  plate  of  the  common  electrical  machine,  the  partridge- 
wood  as  the  rubber,  and  the  steam  as  the  rubbing  power.  The  electricity 
produced  by  this  engine  is  not  so  remarkable  for  its  high  intensity  as  for  its 
enormous  quantity.  The  maximum  spark  obtained  by  Mr.  Armstrong  in  the 
open  air  was  22  in.,  the  extreme  length  under  present  circumstances  has  been 
12  or  14  in.;  but  the  1  lrge  battery  belonging  to  the  Polytechnic  Institution, 
exposing  nearly  80  ft.  of  coated  glass,  which  under  favourable  circumstances 


THE  HYDRO-ELECTRIC  MACHINE. 


3°5 


was  charged  by  the  large  plate  machine,  7  ft.  in  diameter,  in  about  50  seconds, 
is  commonly  charged  by  the  hydro-electric  engine  in  6  or  8  seconds.  The 
sparks  which  pass  between  the  boiler  and  a  conductor  are  exceedingly  dense 
in  appearance,  and,  especially  when  short,  more  resemble  the  discharge  from 
a  coated  surface  than  from  a  prime  conductor.  They  not  only  ignite  gun¬ 
powder,  but  even  inflame  paper  and  wood  shavings  when  placed  in  their 
course  between  two  points.  In  the  151st  number  of  the  ‘Philosophical 
Magazine,’  a  series  of  electrolytic  experiments  made  with  this  machine  are 
described  by  Mr.  Armstrong.  True  polar  decomposition  of  water  was  effected 
in  the  clearest  and  most  decisive  manner,  not  only  in  one  tube,  but  in  ten 
different  vessels,  arranged  in  series,  and  filled  respectively  with  distilled  water, 
acidified  with  sulphuric  acid,  solution  of  sulphate  of  soda  tinged  blue,  and 
red  solution  of  sulphate  of  magnesia,  &c.,  &c.,  and  the  gases  were  obtained 
in  sufficient  quantities  for  examination. 

“The  following  curious  experiments  are  likewise  described: 

“Two  glass  vessels  containing  water  were  connected  together  by  means  of 
wet  cotton.  On  causing  the  electric  current  to  pass  through  the  glasses,  the 
water  rose  above  its  original  level  in  the  vessel  containing  the  negative  pole, 
and  subsided  below  it  in  that  which  contained  the  positive  pole,  indicating  the 
transmission  of  water  in  the  direction  of  a  current  flowing  fiom  the  positive  to 
the  negative  wire.  Two  wine-glasses  were  then  filled  nearly  to  the  edge  with 
distilled  water,  and  placed  about  4-ioths  of  an  inch  from  each  other,  being 
connected  together  by  a  wet  silk  thread  of  sufficient  length  to  allow  a  portion 
of  it  to  be  coiled  up  in  each  glass.  The  negative  wire,  or  that  which  com¬ 
municated  with  the  boiler,  was  inserted  in  one  glass,  and  the  positive  wire,  or 
that  which  communicated  with  the  ground,  was  placed  in  the  other.  The 
machine  being  then  set  in  action,  the  following  singular  effects  presented 
themselves : 

“  1.  A  slender  column  of  water,  inclosing  the  silk  thread  in  its  centre,  was 
instantly  formed  between  the  two  glasses,  and  the  silk  thread  began  to  move 
from  the  negative  towards  the  positive  pole,  and  was  quickly  all  drawn  over 
and  deposited  in  the  positive  glass. 

“  2.  The  column  of  water,  after  this,  continued  for  a  few  seconds  suspended 
between  the  glasses  as  before,  but  without  the  support  of  the  thread ;  and  when 
it  broke,  the  electricity  passed  in  sparks. 

“3.  When  one  end  of  the  silk  thread  was  made  fast  in  the  negative  glass, 
the  water  diminished  in-the  positive  glass,  and  increased  in  the  negative  glass, 
showing,  apparently,  that  the  motion  of  the  thread,  when  free  to  move,  was 
in  the  reverse  direction  of  the  current  of  water. 

“4..  By  scattering  some  particles  of  dust  upon  the  surface  of  the  water,  it 
was  soon  perceived  by  their  motions  that  there  were  two  opposite  currents 
passing  between  the  glasses,  which,  judging  from  the  action  upon  the  silk 
thread  in  the  centre  of  the  column,  as  well  as  from  other  less  striking  indica¬ 
tions,  were  concluded  to  be  concentric,  the  inner  one  flowing  from  negative  to 
positive,  and  the  outer  one  from  positive  to  negative.  Sometimes  that  which 
was  assumed  to  be  the  outer  current  was  not  carried  over  into  the  negative 
glass,  but  trickled  down  outside  of  the  positive  one,  and  then  the  water,  instead 
of  accumulating,  as  before,  in  the  negative  glass,  diminished  both  in  it  and  in 
the  positive  glass. 

“  5.  After  many  unsuccessful  attempts,  Mi.  Armstrong  succeeded  in  causing 
the  water  to  pass  between  the  glasses  without  the  intervention  of  a  thread  for 

29 


3°6 


ELECTRICITY. 


several  minutes,  at  the  end  of  which  time  he  could  not  perceive  that  any 
material  variation  had  taken  place  in  the  quantity  of  water  contained  in  either 
glass.  It  appeared  that  the  two  currents  were  nearly,  if  not  exactly,  equal, 
while  the  inner  one  was  not  retarded  by  the  friction  of  the  thread.  Mr.  Arm¬ 
strong  likewise  succeeded  in  coating  a  silver  com  with  copper,  in  deflecting  the 
needle  of  a  galvanometer  between  20°  and  30°,  and  in  making  an  electro¬ 
magnet  by  means  of  the  electricity  from  this  novel  machine. 

“  Extraordinary  as  is  the  power  of  the  Polytechnic  machine,  it  was  after¬ 
wards  entirely  eclipsed  by  a  similar  apparatus  constructed  at  Newcastle  under 
the  direction  of  Mr.  Armstrong,  and  sent  out  to  the  United  States  ol  America. 
In  the  arrangement  of  this  machine,  the  boiler  of  which  is  not  larger  than  that 
at  the  Polytechnic  Institution,  Mr.  Armstrong  introduced  certain  improve¬ 
ments,  suggested  by  the  working  of  the  latter,  and  which  had  reference  to 
those  parts  of  the  apparatus  more  immediately  concerned  in  the  production  of 
the  electricity,  viz.,  the  escape  apertures  and  the  condensing  pipes.  It  was 
found  to  be  a  matter  of  extreme  nicety  to  adjust  the  quantity  of  water  depo¬ 
sited  in  the  condensing  pipes,  so  as  to  obtain  the  maximum  excitation  of  elec¬ 
tricity.  If,  on  the  one  hand,  there  be  an  excess  of  water,  then  two  results 
will  ensue,  each  tending  to  lessen  the  electricity  produced:  —  1st,  the  mean 
density  of  the  issuing  current  of  steam  and  water  is  increased,  which  causes 
the  velocity  of  efflux,  and  consequent  energy  of  the  friction,  to  be  diminished; 
and,  2ndly,  the  ejected  steam-cloud  is  rendered  so  good  a  conductor  by  the 
excess  of  moisture,  that  a  large  proportion  of  the  electricity  manifested  in  the 
cloud  retrocedes  to  the  boiler,  and  neutralizes  a  corresponding  proportion  of 
the  opposite  element.  On  the  other  hand,  if  the  quantity  of  water  be  too 
small,  then,  although  each  particle  of  water  may  be  excited  to  the  fullest  extent, 
the  effect  is  rendered  deficient,  in  consequence  of  the  insufficient  number  of 
aqueous  particles  which  undergo  excitation. 

“In  the  Polytechnic,  arrangement  for  condensation  of  the  steam  in  the 
tubes  is  effected  by  contact  with  the  external  air;  and  when  the  density  of  the 
steam  in  the  boiler  is  diminished  rapidly,  they  do  not  cool  down  with  sufficient 
rapidity  to  condense  the  requisite  quantity  of  water.  To  remedy  this  defect 
in  the  American  machine,  Mr.  Armstrong  adopted  a  method  of  condensing 
by  the  application  ot  cold  water.  A  number  of  cotton  threads  were  suspended 
from  eacli  condensing  pipe  into  a  trough  of  water,  from  which,  by  capillary 
attraction,  just  as  much  water  was  lifted  as  was  required  for  the  cooling  of  the 
pipe,  since  it  was  easy,  by  increasing  or  diminishing  the  quantity  of  cotton, 
to  increase  or  diminish  the  supply  of  cold  water  ;  and  this  method  of  keeping 
down  the  temperature  proved  so  effective,  that  two  or  three  times  the  number 
of  jets  that  were  before  used  could  now  be  employed.  The  number  in  the 
American  machine  was  140,  ranged  in  two  horizontal  rows,  one  above  the 
other,  on  the  same  side  of  the  machine.  The  sparks  obtained,  though  not 
longer  than  those  upon  the  London  machine  when  it  stood  in  the  open  air, 
succeeded  each  other  with  three  or  four  times  the  rapidity,  and,  even  under 
unfavourable  circumstances,  charged  a  Leyden  battery,  consisting  of  thirty-six 
jars,  containing  33  ft.  ot  coated  surface,  to  the  utmost  degree  that  the  battery 
could  bear,  upwards  of  sixty  times  in  a  minute,  being  equivalent  to  charging 
nearly  2000  ft.  of  coated  surface  per  minute,  which  is  at  least  twenty  times 
greater  than  the  utmost  effect  that  could  be  obtained  from  the  largest  glass 
electrical  machine  ever  constructed.” 

The  Polytechnic  apparatus,  itself  unique,  enormous,  and  powerful,  was  well 


THE  HYDRO-ELECTRIC  MACHINE. 


3  07 


adapted  for  the  purposes  of  the  Institution,  but  could  not  be  carried  about  or 
fitted  up  in  another  lecture-room.  The  writer  had  a  portable  apparatus  fitted 
up,  which  gave  safely,  on  the  small  scale,  all  that  could  be  w  tncssed  with  the 
great  hydro-electric  steam  machine.  It  consisted  of  a  cylindrical  furnace 
and  strong  copper  boiler,  supported  on  a  stool  with  stout  glass  legs,  each  of 
which  rested  on  a  disc  of  shellac.  The  boiler  was  provided  with  a  safety-valve 
and  all  necessary  taps,  and  proceeding  from  it,  and  fitted  with  a  ball-and-socket 
joint,  was  a  copper  tube,  1  in.  in  diameter-,  curved  round,  and  having  a  hollow 
copper  ball  at  the  end,  to  which  three  stop-cocks  were  fitted.  Whilst  steam 
was  getting  up,  the  copper  tube  was  left  off  the  boiler,  and  only  screwed  on 
just  before  the  experiments  were  shown. 

The  chimney  of  the  furnace  was  so  arranged  that  the  portion  connected 
directly  with  the  furnace  could  be  removed,  disclosing  a  square  iron  box,  into 
which  a  few  pieces  of  burning  charcoal  were  placed,  so  that,  when  the  copper 
tube  and  ball  were  screwed  on,  the  first  stop-cock  exactly  faced  the  iron  box 
containing  the  charcoal;  and,  of  course,  when  the  steam  was  turned  on,  it 
blew  out  of  the  latter  into  the  charcoal,  and,  causing  the  charcoal  to  burn 
with  greater  rapidity,  created  a  good  draught,  which  carried  off  the  steam,  and 
prevented  it  doing  harm  to  the  other  electrical  apparatus,  which  had  to  be 
kept  dry  and  warm. 


Fig.  256. — Portable  Apparatus  for  showing  the  Electricity  of  Watery  Steam 

A  is  the  copper  boiler,  safety-valve,  copper  curved  tube,  with  hollow  ball  and 
three  stop-cocks ;  the  lower  one  enables  the  operator  to  remove  condensed 
water,  the  upper  one  to  introduce  any  different  fluid;  the  third  contains  the 
jet  made  of  hard  partridge-wood  (F  ig.  257),  from  which  the  watery  steam 
escapes  into  the  charcoal-box  and  chimney,  D  D.  The  dotted  lines,  C  C,  show 
the  portion  of  the  chimney  removable  before  the  experiments  commence,  in 
order  to  insulate  the  furnace  B,  which  stands  on  a  stool  with  strong  glass  legs, 
resting  on  plates  of  shellac. 

The  operator  must  remember  to  keep  a  sufficient  quantity  of  damp  sand  in 
the  bottom  of  the  ash-pit,  which  should  be  regularly  wetted  by  the  assistant,  or 
the  stool  may  catch  fire,  and  great  confusion  caused  by  this  untoward  result. 
The  chimney  n  d  is  rendered  independent  of  all  extraneous  support  by  being 
attached  to  a  strong  iron  pillar  with  claw  feet,  screwed  to  the  floor  with  (e  e) 

20 — 2 


ELECTRICITY. 


3°8 


stage-screws,  /.<?.,  spiral  screws  with  handles,  much  used  for  theatrical  purposes, 
to  support  small  bits  of  scenery  on  a  stage. 

The  boiler  being  insulated,  and  the  steam  up  to  a  pressure  of  at  least  30  lbs. 
on  the  square  inch,  a  number  of  interesting  experiments  may  be  performed. 


Fig.  257. — Section  of  the  Jet  used  for  the  Hydro-Electric  Machine , 

3;ing  a  conical  plug  of  hard  wood  (partridge-wood  is  preferred),  terminated  by  a  brass  mouth- piece.  The 

shaded  parts  are  brass. 


I.  Mere  emission  of  d?y  steam  produces  no  electricity,  and  will  hardly 
affect  the  gold  leaves  of  an  electroscope. 

II.  The  copper  ball  is  now  purposely  cooled  a  little  by  pouring  cold  water 
and  applying  a  wet  flannel  to  it,  so  as  to  obtain  some  condensed 
water ;  and  now,  when  the  steam  is  turned  on,  the  usual  signs  of 
electrical  excitement  become  apparent,  and  sparks  are  easily  procur¬ 
able.  The  handles  of  the  stop-cock  must  be  covered  with  flannel,  or 
the  operator  will  be  unable  to  manipulate  the  opening  and  shutting 
of  them.  The  watery  steam,  rushing  through  the  tube,  evolves  elec¬ 
tricity,  because  the  particles  of  water  forced  through  by  the  jet  of  steam 
rub  against  the  inside  of  the  jet,  thus  proving  in  a  satisfactory  manner 
that  friction  is  the  exciting  cause,  and  not  the  mere  change  of  form 
of  water  into  steam.  The  copper  boiler,  whilst  the  steam  is  issuing, 
is  negatively  electrified;  the  issuing  steam,  positively. 

III.  The  steam  being  raised  to  50  lbs.  on  the  square  inch,  the  electric  spark, 

the  inflammation  of  combustible  matter,  and  the  charging  of  the 
Leyden  jar,  can  be  displayed,  the  boiler  and  steam  remaining  in  the 
same  state  of  electricity. 

IV.  Altering  the  rubbing  fluid,  by  substituting  oil  for  the  water  in  the  copper 

globe  (easily  done  by  pouring  in  a  few  drops  of  oil  of  turpentine 
through  the  upper  stop-cock),  changes  the  state  of  the  electricity  of 
the  boiler  from  negative  to  positive,  and  the  steam  from  positive  to 
negative,  because  the  globules  of  water  become  coated  with  oil,  and 
thus  expose  a  different  surface  against  the  rubber,  viz.,  the  inside  of 
the  hard  partridge-wood  jet. 

V.  The  electrical  exaltation  is  destroyed  for  a  time  by  putting  a  solution  of 
common  salt  into  the  copper  globe,  because  the  particles  of  water 
are  then  made  good  conductors,  and  as  fast  as  the  electricity  is  ob¬ 
tained  it  is  neutralized  (returned  again  to  the  boiler),  just  like  rubbing 
a  piece  of  sealing-wax  with  a  damp  flannel.  The  gradual  rise  and 
return  of  the  electrical  force  is  shown,  as  the  conducting  matter,  the 
salt,  is  blown  out  of  the  copper  globe,  as  if  the  damp  flannel  had  been 
dried,  and  thus  lost  its  conducting  power. 

VI.  Dry  steam  or  dry  air  will  not  excite  electricity  whilst  rushing  through  a 
tube ;  this  is  easily  proved  by  getting  the  copper  tube  and  globe  as 
hot  as  possible,  and  then  allowing  the  steam  to  issue  from  the  jet. 


SUMMARY  OF  LAWS. 


3°  9 


So  also  with  air :  the  mere  fact  of  allowing  air  to  rub  against  the 
inside  of  the  nozzle  of  a  common  pair  of  bellows  will  not  eliminate 
the  electric  force;  but  if  a  little  whitening  or  powdered  chalk  is  in¬ 
troduced,  as  a  substitute  for  the  watery  particles  in  the  steam  experi¬ 
ment,  the  electricity  is  produced,  and  is  shown  distinctly  if  the 
whitening  is  blown  out  on  to  the  cap  of  the  electroscope. 

VII.  By  connecting  an  insulated  platinum  capsule,  containing  water,  by  a 
wire,  with  an  electroscope,  and  evaporating  the  water,  no  electricity 
can  be  rendered  evident ;  if,  however,  a  piece  of  red-hot  charcoal  is 
placed  in  the  platinum  capsule,  and  a  little  water  suddenly  poured 
upon  it,  and  provided  the  ebullition  is  sufficiently  violent  to  cause  the 
particles  of  water  to  rub  against  the  sides  of  the  capsule,  then  elec¬ 
tricity  is  sometimes  eliminated. 

From  these  experiments  it  may  be  concluded  that  evaporation  unattended 
by  friction,  as  from  the  surface  of  the  oceans,  rivers,  lakes,  is  not  a  source 
from  whence  electricity  in  nature  is  obtained,  and  we  must  therefore  look  to 
some  other  cause  for  the  explanation  of  the  production  of  atmospherical  elec¬ 
tricity. 

— - - ♦ - - - 

SUMMARY  OF  THE  LAWS  OF  ELECTRICAL  ACCUMULATION. 

The  young  students  who  wish  to  travel  easily  through  the  chapters  on  voltaic 
electricity,  magnetism,  and  electro-magnetism  will  do  well  to  make  themselves 
well  acquainted  with  the  laws  which  relate  to  frictional  electricity,  as  they  will 
find  them  reproduced  in  more  complicated  forms  as  they  proceed  with  the 
consideration  of  the  most  important  branches  of  science,  with  which  all  well- 
educated  persons  should  be  acquainted. 

I.  Experiments  would  show,  and  especially  those  which  relate  to  the 
velocity  of  the  passage  of  an  electrical  discharge  through  a  copper  wire 
half  a  mile  in  length,  performed  by  Sir  Charles  Wheatstone,  p.  267, 
that  the  idea  of  the  existence  of  two  forces,  the  one  called  “  vitreous  ” 
and  the  other  “resinous”  electricity,  seems  to  be  more  rational  and 
better  capable  of  proof  than  the  I'ranklinian  theory  that  supposes 
the  existence  of  one  fluid  only ;  and  this  idea  is  further  supported  by 
Armstrong’s  curious  experiments  with  the  Polytechnic  hydro-electric 
machine,  paragraphs  1  to  5,  page  275. 

II.  Similar  electricities  repel,  dissimilar  attract,  each  other. 

III.  There  is  no  absolute  difference  between  insulators  and  conductors,— it 

is  shown  that  they  may  both  assume  polarity ;  but,  in  the  former  case, 
the  polarity  lasts  only  so  long  as  the  disturbing  cause  exists;  in  the 
latter,  as  with  glass  and  resin,  the  polarity  set  up  is  maintained. 
These  are  called  dielectrics,  because  they  arc  capable  of  polarization. 

IV.  Electrical  induction  means  that  disturbance  of  electrical  equilibrium 

which  occurs  when  an  electrified  body  is  brought  towards  another 
which  is  in  a  quiescent  state. 

V.  Faraday’s  theory  of  induction  has  overturned  all  previous  hypotheses. 
“  Electrical  induction  is  an  action  of  contiguous  particles.  ’  Every 
particle  of  air  between  a  piece  of  excited  glass  and  the  cap  of  an 
electroscope  is  supposed  to  be  in  a  polar  state. 


ELECTRICITY. 


3 10 


As  long  as  the  particles  maintain  their  polarization,  insulation  is 
secured ;  but  when  the  particles  discharge  themselves  one  into  the 
other,  then  a  neutralization  occurs,  and  the  non-maintenance  of 
polarization  is  called  conduction. 

Even  a  Faraday  could  occasionally  write  vaguely.  It  is  sometimes 
better  to  take  the  epitome  of  a  philosopher’s  assumptions  through 
another  mind,  and  this  want  is  admirably  supplied  by  the  late  Pro¬ 
fessor  Daniell,  of  King’s  College,  London  : 

“  Up  to  the  date  of  his  discovery,  the  phenomena  of  induced  elec¬ 
tricity  wrere  supposed  to  arise  from  an  action  of  a  charged  body  upon 
others  at  a  distance,  in  straight  lines,  through  non-conducting  media, 
the  particles  of  which  were  assumed  to  be  unaffected  by  it ;  he  has 
shown  induction,  on  the  contrary,  to  be  an  action  of  contiguous  par¬ 
ticles  throughout,  capable  of  propagation  in  curved  lines,  and  to  be 
concerned  in  all  electrical  phenomena ;  having  in  reality  the  character 
of  a  first,  essential,  and  fundamental  principle.  .  .  It  was  formerly 
supposed  that  the  electric  fluid  was  confined  to  the  surfaces  of  bodies 
by  the  mechanical  pressure  of  the  non-conducting  air,  in  the  midst 
of  which  all  our  experiments  are  carried  on;  but  the  fact  is  that  the 
electric  force,  originally  appearing  at  a  certain  place,  is  propagated 
to,  and  sustained  at,  a  distance  through  the  intervention  of  the  con¬ 
tiguous  particles  of  air,  each  of  which  becomes  polarized,  as  in  the 
case  of  insulated  conducting  masses,  and  appears  in  the  inducteous 
body,  i.e.,  the  body  under  induction  as  a  force  of  the  same  kind 
exactly  equal  in  amount,  but  opposite  in  its  directions  and  tendencies.” 

VI.  Electricity  is  found  to  reside  on  the  surface  of  an  insulated  metallic 
conductor — a  natural  sequence  of  the  polarization  of  particles.  The 
difference  in  form,  as  between  a  ball  and  a  point,  so  far  as  their  rela¬ 
tion  to  an  electrical  charge  is  concerned,  is  explicable  by  the  theory 
of  contiguous  particles. 

“  It  was,”  says  Daniell,  “by  an  apparatus  constructed  on  similar 
principles  to  the  electrophorus  (p.  245)  that  Faraday  brought  to  the  test 
of  experiment  his  theoretical  anticipation  that  inductive  action,  taking 
place  invariably  through  the  intermediate  influence  of  intervening 
matter,  would  be  found  to  be  exerted,  not  in  the  direction  of  straight 
lines  only,  as  had  always  been  assumed,  but  also  in  curved  lines. 

“A  cylinder  of  solid  shellac,  of  about  1  in.  in  diameter  and  7  in.  in 
length,  was  fixed  in  a  wooden  foot ;  it  was  made  concave,  and  capped 
at  its  upper  extremity,  so  that  a  brass  ball  or  hemisphere  could  stand 
upon  it.  The  upper  half  of  the  stem  having  been  excited  resinously, 
by  friction  with  warm  flannel,  a  brass  ball  was  placed  on  the  top,  and 
then  the  whole  arrangement  examined  by  the  carrier  ball  or  proof- 
plane  and  Coulomb’s  electrometer  (p.  229).  For  this  purpose  the 
carrier  ball  was  applied  to  various  parts  of  the  ball;  the  two  were 
uninsulated  whilst  in  contact,  or  in  position,  then  insulated,  separated, 
and  the  charge  of  the  carrier  examined  as  to  its  nature  and  force. 
Of  course,  whatever  general  state  the  carrier  acquired  in  any  place 
where  it  was  uninsulated  and  then  insulated,  it  retained  on  removal 
from  that  place,  and  the  distribution  of  the  force  upon  the  surface  of 
the  inducteous  body  while  under  the  influence  of  the  inductive  was 
ascertained.  The  charges  taken  from  the  ball  in  this  its  uninsulated 


SUMMARY  OF  LAWS. 


31 1 


state  were  always  vitreous,  or  of  the  contrary  character  to  the  elec¬ 
tricity  of  the  lac.  When  the  contact  was  made  at  the  under  part  of 
the  ball,  the  measured  degree  of  force  was  51 2°;  when  in  a  line  with 
its  equator,  270°;  and  when  on  the  top  of  the  ball,  1300.” 


Fig.  258. — Faraday's  Experiment , 

Proving  that  the  polarization  of  the  particles  of  air 
may  occur  in  curved  as  well  as  in  straight  lines. 


I 

F IG.  259. — Faraday's  Apparatus  for  de¬ 
termining  the  specif  c  or  particular 
inductive  power  belonging  to  various 
substances. 

a,  b,  the  two  brass  spheres,  one  within  the  other,  a 
being  supported  be  a  brass  wire,  c,  passing  through 
a  shellac  rod,  which  latter  insulates  a.  and  prevents 
it  communicating  with  b.  The  space  between  a 
and  B  can  he  tilled  with  any  solid,  liquid,  or  gas¬ 
eous  die'ectric.  e,  the  stop-cock,  which  screws 
into  the  air-pump,  if  necessary. 


The  shellac  electrophorus  with  its  ball  is  here  exhibited  (Fig.  258), 
together  with  the  positions  of  the  carrier  ball  referred  to.  When 
placed  at  d,  the  effect  produced  was  5 1 2° ;  at  c,  270° ;  at  b,  1 30°.  Even 
in  the  position  z’the  proof  or  carrier  ball  became  inducteous  ;  and  ate* 
it  was  affected  in  the  highest  degree,  and  gave  a  result  above  iooo0. 

VII.  Specif c  Induction. — If  one  body  capable  of  maintaining  polarization 
can  assume  this  condition  quicker  than  another,  it  must  be  apparent 
that  a  resisting  force  of  some  kind  exists,  which  causes  insulating 
substances  to  vary  in  this  respect. 

Faraday  ascertained  this  variable  resistance  by  means  of  an  appa¬ 
ratus  (Fig.  259)  consisting  essentially  of  two  brass  spheres,  placed 
one  within  the  other,  conducting  communication  between  them  being 
prevented  by  proper  means.  The  intervening  space  between  one 
sphere  and  another  could  then  be  filled  with  a  variety  of  substances, 
solid,  fluid,  and  gaseous. 

Faraday  used  two  of  the  instruments  (Fig.  259),  and  a  certain 
charge  having  been  given  to  one  of  these,  after  the  intervening  space 
had  been  filled  with  the  substance  under  investigation,  it  was  con¬ 
nected  with  the  second  instrument,  containing  air  ;  thus  the  latter 
became  the  standard  of  comparison  used  throughout  the  experiments; 
and  the  intensity,  rs  before,  was  estimated  by  the  carrier  or  proof 


312 


ELECTRICITY. 


ball  and  Coulomb’s  electrometer.  The  inductive  apparatus  was  in 
effect  a  Leyden  jar,  with  the  advantage  that  the  dielectric,  represented 
in  the  latter  case  by  glass,  could  be  removed  at  pleasure,  and  other 
bodies  substituted.  With  this  apparatus  Faraday  determined  the 
inductive  powers  of  a  number  of  substances,  and  his  experiments 
have  been  extended  and  verified  by  Sir  William  Snow  Harris. 


Substance. 

Air  . 

Rosin 

Pitch  . 

Beeswax 

Glass . 

Sulphur 

Shellac 


Coinparat 


ve  Specific  Inductive  Power. 


I'OO 

177 

r8o 
r86 
i-9o 
1 ‘93 
1  '95 


All  gases,  whatsoever  may  be  their  nature,  have  the  same  specific 
inductive  power  as  air;  no  variation  in  the  moisture,  or  temperature, 
or  density  of  the  gases  affects  the  uniformity  of  their  property  in  this 
respect. 

VIII.  Electricity  stored  in  a  Leyden  jar  can  be  measured  into  it,  if  neces¬ 
sary,  by  a  beautiful  contrivance  of  Harris,  called  the  unit  or  standard 
jar ;  it  is,  of  course,  similar  in  principle  to  Lane’s  discharging  electro¬ 
meter,  page  261.  The  unit  Leyden  jar  is  a  very*  small  one,  and, 
mounted  on  a  glass  rod,  the  outside  has  a  brass  cap  carrying  a  brass 
rod,  which  is  placed  at  any  required  distance  from  the  wire  and  ball 
coming  from  the  interior  of  the  miniature  jar.  According  to  the 
Franklinian  experiment,  page  251,  every  charge  sent  to  the  outside 
of  the  unit  jar  sets  free  from  the  inside  an  equivalent  proportion  of 
vitreous  electricity;  and  directly  the  charge  in  the  little  jar  is  of  suffi¬ 
cient  intensity  to  break  through  the  intervening  thickness  of  air,  it 
discharges  itself  with  the  usual  snapping  noise. 

IX.  With  Harris’s  unit  jar  (Fig.  260)  and  balance,  the  following  facts  have 
been  ascertained  : 


Fig.  260. — Harris’s  Unit  Jar. 

«•  Te  conductor  of  the  electrical  machine  connected  with  the  outside  of  the  unit  jar,  b;  the  inside, 
,  being  connected  >  ith  a  large  I.eyden  jar,  every  time  the  little  jar  discharges  itself  betwetn  b  and  », 
a  unit  or  definite  quantity  of  electrical  force  has  passed  into  the  larger  jar. 

1  he  area  of  the  charged  surface  remaining  constant,  the  attraction 


SUMMARY  OF  LAWS. 


3 1 3 


between  the  two  discs  of  the  balance  (see  page  231)  increases  as  the 
square  of  the  quantity.  The  intensity  of  the  charge  being  main- 
tained  at  one  fixed  point,  and  the  distance  between  the  discs  altered, 
the  attractive  force  varies  inversely  as  the  square  of  the  distance. 

Coulomb’s  laws,  already  detailed,  can  only  be  regarded  as  general 
when  they  are  confined  to  electrized  molecules  or  points ;  they  are 
again  repeated  here  for  the  sake  of  the  student,  who  may  wish  to 
remember  the  chief  laws.  First  law,  “Two  electrized  bodies  attract 
and  repel  each  other  with  a  force  which  is  inversely  proportional  to 
the  square  of  the  distance  that  separates  them.” 

The  force  with  which  two  bodies  that  possess  different  electricities 
attract  each  other  is  inversely  proportional  to  the  square  of  the  dis¬ 
tance  by  which  they  are  separated. 

X.  The  discharge  of  an  electrical  accumulation  may  take  place  in  various 
ways;  viz., 

1.  By  conduction, 

2.  By  disruption, 

3.  By  convection. 

The  first  is  the  most  simple,  as  when  a  brass  rod  is  held  in  the 
hand,  and  laid  upon  the  conductor  of  an  electrical  machine  in  full 
action. 

The  second  involves  the  charge  of  particles,  and  their  displace- 


FlG.  261. — A  Current  of  Air  set  in  motion  from  the  Electric  Point , 

And,  by  convection,  carrying  the  electricity  to  the  flame  of  the  candle,  when  it  is  dissipated  and  lost  by 

the  heated  and  rarefied  air. 


ment  in  a  gradual  and  steady  manner,  as  by  brushes  or  glow;  or  in 
a  violent  degree,  as  with  a  spark  passing  through  the  air,  or  causing 
the  fracture  of  a  thin  Leyden  jar,  which  has  been  too  highly  charged. 

The  third  is  special  and  peculiar,  and  involves  motion  ;  it  is,  there¬ 
fore,  called  a  “carrying  discharge.”  Faraday  illustrated  it  by  insu¬ 
lating  and  electrifying  a  large  copper  boiler,  3  ft.  in  diameter,  to  a 
limit  just  within  that  which  would  produce  the  brush  or  moderate 
disruptive  discharge.  A  brass  ball,  2  in.  in  diameter,  when  sus¬ 
pended  by  a  silk  thread  and  held  within  2  in.  of  the  boiler,  became 
charged,  although  insulated  the  whole  time.  As  its  electricity  was 
contrary'  to  that  of  the  boiler,  the  effect  would  be,  with  a  light  ball, 
that  it  will  be  attracted,  and  then  fly  off  to  the  nearest  conductor,  and 


ELECTRICITY. 


3U 


thus,  like  dust  or  any  small  particles  capable  of  easy  motion,  would 
gradually,  by  convection,  carry  away  the  charge. 

A  brush  discharge  may  be  frequently  changed  to  a  glow,  by  setting 
up  a  current  of  air  in  the  same  direction  as  that  taken  by  the  brush 
discharge;  and  this  effect  may  be  reversed,  and  a  glow  converted 
into  a  brush,  by  preventing  the  access  of  currents  of  air. 

Lateral  Discharge. 

In  consequence  of  the  resistance  offered,  even  by  metals,  to  the  progress  of 
electricity,  there  is  always  a  tendency  in  any  electrical  discharge  to  divide 
itself  if  there  are  many  contiguous  conductors  in  the  same  line  or  path; 
and  thus  sparks  or  flashes  will  occur  when  least  expected,  and,  in  the  case  of 
ships  of  war  or  powder-magazines,  may  do  some  harm  if  they  are  struck  by 
lightning,  although  they  may  be  supplied  with  lightning-conductors.  The 
subject  of  lateral  discharge  received  considerable  attention  from  the  late  Sir 
William  Snow  Harris  and  Mr.  Charles  V.  Walker,  and  the  result  of  their  dis¬ 
cussions  was  the  more  careful  protection  of  Her  Majesty’s  ships  by  taking  care 
to  connect  all  masses  or  bars  of  metal  with  the  main  conductor,  so  that  no 
accidental  division  shall  occur  anywhere;  and  thus  all  chance  of  flashes  or 
sparks  are  prevented.  The  following  experiment  of  Dr.  Miller*  serves  to 
illustrate  this  point : 


Charge  a  Leyden  jar,  and  arrange  a  metallic  wire,  w,  from  120  to  150  ft.  in 
length,  so  as  to  act  the  part  of  discharger ;  at  the  same  time  open  a  short  path 
for  the  discharge  to  the  outer  coating,  by  bringing  the  balls  a,  b  within  a  short 
distance  of  each  other.  Under  this  arrangement  a  portion  of  the  electricity 
takes  the  shorter  course  from  a  to  b ,  and  overcomes  the  high  resistance  of  the 
stratum  of  air  interposed  between  the  balls,  owing  to  the  resistance  experienced 
by  the  discharge  to  its  passage  along  the  continuous  conducting  wire  W. 


*  Miller’s  “  Elements  of  Chemistry,”  vol,  i.,  p.  43a. 


VOLTAIC  ELECTRICITY. 


Fig.  263. — Galvan? s  Experiment  with  the  Nerves  and  Muscles  of  the  dead 

Frog 

(As  exhibited  on  the  disc  at  the  FoH  technic). 


VOLTAIC,  GALVANIC,  OR  DYNAMICAL 
ELECTRICITY. 

It  always  seems  quite  natural,  and  taking  things  in  their  right  order,  to  com¬ 
mence  this  subject  by  speaking  of  that  famous  illustration  of  animal  electri¬ 
city  primarily  discovered  by  Galvani,  who  ascertained  that  by  touching  the 
lumbar  nerves  of  a  frog,  or  lower  part  of  the  spine  of  a  frog,  recently  killed, 
with  a  clean  copper  wire,  and  the  muscles  with  a  zinc  wire,  and  then  bringing 
the  two  metals  in  contact,  that  a  current  of  electricity  was  evolved,  which  was 
instantly  rendered  evident  by  the  frog-electroscope,  the  limbs  being  always 
convulsed  in  the  most  curious  manner. 

Galvani  thought  that  the  nerves  and  muscles  of  all  animals  were  in  oppo- 


ELECTRICITY. 


316 


site  states  of  electricity,  and  that  the  effect  occurred  only  at  the  moment  when 
the  two  opposite  forces  rush  together  and  neutralize  each  other;  but  it  was 
soon  shown  that  the  convulsions  were  due  to  the  effect  of  a  current  of  elec¬ 
tricity,  however  feeble,  set  up  when  the  two  metals  touched  each  other  in  the 
presence  of  a  third  element,  viz.,  the  liquid,  containing  chloride  of  sodium,  with 
which  the  limbs  ot  the  recently  killed  frog  would  necessarily  be  moistened  ;  it 
was,  in  short,  the  oxidation  of  the  zinc  wire  that  produced  the  current,  and 
the  prepared  limbs  of  the  frog  represented  only  the  electroscope  that  rendered 
the  electrical  disturbance  evident. 

The  biographer  of  Lewis  Galvani,  in  “  Rees’s  Cyclopaedia,”  states  that  he  was 
born  in  173 7,  at  Bologna. 

In  his  early  youth  he  showed  a  great  propensity  to  religious  austerities ;  but, 
being  dissuaded  from  entering  into  an  order  of  monks,  whose  convent  he  fre¬ 
quented,  he  directed  his  attention  to  the  study  of  medicine.  He  pursued  this 
study  under  able  masters,  and  gained  their  esteem,  especially  that  of  Professor 
Galcazzi,  who  received  him  into  his  house  and  gave  him  his  daughter  in  mar¬ 
riage.  In  the  year  1762,  after  having  sustained  an  inaugural  thesis,  “  De 
Ossibus,”  he  was  appointed  public  lecturer  in  the  University  of  Bologna  and 
reader  in  anatomy  to  the  Institute  in  that  city.  By  the  excellence  of  his 
method  of  teaching,  he  obtained  crowded  audiences. 


Fig.  264. — The  prepared  Frog's  Limbs. 


Then  follows  the  story  of  the  soup  made  of  frogs,  which  had  been  recom¬ 
mended  to  his  dearly  loved  wife,  who  was  in  a  declining  state  of  health,  and 
the  accidental  discovery  that  the  limbs  of  the  frog  were  affected  by  the  point 
of  a  scalpel  held  near  the  prime  conductor  of  an  electrical  machine  in  action. 

Matteuchi,  however,  denies  the  originality  of  the  experiment,  and  declares 
that  it  was  performed  many  years  before  the  time  of  Galvani,  in  the  presence 
of  the  Grand  Duke  of  Tuscany,  by  the  celebrated  Swammerdam. 

His  first  publication  on  the  subject  was  printed  for  the  Institute  at  Bologna, 
1791,  and  entitled  “  Aloysii  Galvani  de  viribus  Electricitatis  in  motu  musculari 
Commentarius.”  This  work  immediately  excited  the  attention  of  philosophers, 
both  in  Italy  and  ether  countries,  and  the  experiments  were  repeated  and 
extended. 

In  conjunction  with  his  physiological  inquiries,  the  duties  of  his  professor¬ 
ship  and  his  employment  as  a  surgeon  gave  full  occupation  to  the  industry  of 
Galvani.  In  addition  to  a  number  of  curious  observations  on  the  organ  of 
hearing  in  birds,  which  were  published  in  the  memoirs  of  the  Institute  of 


A LD INI'S  EXPERIMENTS. 


3i7 


Bologna,  he  drew  up  various  memoirs  on  professional  topics,  which  have  re¬ 
mained  unedited. 

He  regularly  held  learned  conversations  with  a  few  literary  friends,  in  which 
new  works  were  read  and  commented  upon.  He  was  a  man  of  a  most  amiable 
character  in  private  life,  and  possessed  of  great  sensibility,  insomuch  that  the 
death  of  his  wife,  in  1790,  threw  him  into  a  profound  melancholy. 

His  early  impressions  on  the  subject  of  religion  remained  unimpaired;  he 
was  always  punctual  in  practising  its  minutest  rites;  and  from  this  cause,  no 
doubt,  he  steadily  refused  to  take  the  civic  oath  exacted  by  the  then  new  con¬ 
stitution  of  the  Cis-Alpine  republic,  and  was  consequently  deprived  of  his 
posts  and  dignities.  In  a  state  of  melancholy  and  poverty,  he  retired  to  the 
house  of  his  brother  James,  a  man  of  very  respectable  character,  and  fell  into 
an  extreme  debility. 

The  repubhean  governors,  probably  ashamed  of  their  conduct  towards 
such  a  man,  passed  a  decree  for  his  restoration  to  his  professorial  chair  and 
its  emoluments ;  but  it  was  too  late. 

He  expired  on  the  5th  of  November,  1798.  But  the  good  philosopher’s  name 
and  works  were  not  to  lie  dead  and  forgotten:  his  nephew,  the  Professor 
Aldini,  of  Bologna,  seeing  the  grief  and  the  sad  end  of  his  uncle,  determined 
to  rescue  h;s  name  from  obscurity,  and  to  defend  Galvani’s  theories,  which  had 
been  attacked  and  repudiated. 

For  this  purpose,  Aldini  travelled  through  France  and  England,  demon¬ 
strating  the  remarkable  physiological  experiments  of  Galvani,  and  so  pleased 
the  professional  authorities  at  Guy’s  Hospital,  in  1803,  that  they  presented 
him  with  a  gold  medal. 

For  a  very  complete  epitome  of  organic  electricity,  the  reader  is  referred  to 
another  work.*  It  may  be  sufficient  here  to  state  that  Aldini  maintained 

that 

“  Muscular  contractions  are  excited  by  the  development  of  a  fluid  (electric) 
in  the  animal  machine,  which  is  conducted  from  the  nerves  to  the  muscles, 
without  the  concurrence  or  action  of  metals. 

“All  animals  are  endowed  with  an  inherent  electricity,  appropriate  to  their 
economy,  which  electricity,  secreted  by  the  brain,  resides  especially  in  the 
nerves,  by  which  it  is  communicated  to  every  part  of  the  body. 

“The  principal  reservoirs  are  the  muscles,  each  of  which  he  regarded  to 
have  two  sides  in  opposite  electric  conditions. 

“  When  a  limb  is  willed  to  move,  the  nerves,  aided  by  the  brain,  draw  from 
the  interior  of  the  muscles  some  electricity ;  discharging  this  upon  their  sur¬ 
face,  they  are  thus  contracted  and  produce  the  required  change  of  position.” 

It  is  a  remarkable  fact,  that  when  an  acid  and  an  alkaline  solution  are 
so  placed  that  their  union  may  be  effected  through  the  substance  of  an  animal 
membrane  or,  indeed,  any  other  porous  diaphragm,  a  current  of  electricity  is 
evolved,  the  causes  of  which  disturbance  of  electric  equilibrium  have  already 
been  investigated.  Now,  with  the  exception  of  the  stomach  and  caecum,  the 
whole  extent  of  the  mucous  membrane  is,  in  the  human  subject,  bathed  with  an 
alkaline  mucous  fluid,  and  the  external  covering  of  the  body,  the  skin,  is  as 
constantly  exhaling  an  acid  fluid,  except  in  the  axillary  and,  perhaps,  pubic 
regions.  The  mass  of  the  animal  frame  is  thus  placed  between  two  great 


*  “The  Elements  of  Natural  Philosophy,”  by  Golding  Bird,  M.A.,  and  Charles  Brooke,  M.A-  John 

Churchill,  New  Burlington  Street. 


ELECTRICITY. 


3t8 


envelopes,  the  one  alkaline  and  the  other  acid,  meeting  only  at  the  external 
outlets.  This  arrangement  has  been  shown  by  Donne  to  be  quite  competent 
to  the  evolution  of  electricity,  and,  accordingly,  he  found  that  if  a  platinum 
plate,  connected  with  the  galvanometer,  be  held  in  the  mouth,  whilst  a  second 
be  pressed  against  the  moist  perspiring  surface  of  the  body,  the  needles  will 
instantly  traverse,  as  they  did  in  the  experiment  just  shown  with  an  acid  and 
an  alkali. 

The  current  thus  detected  by  Donne  at  once  explains  the  cause,  and  con¬ 
firms  the  accuracy,  of  the  celebrated  experiment  of  Aldini,  in  which  he  excited 
convulsions  in  a  frog  by  holding  its  foot  in  the  moistened  hand,  and  allowing 
the  sciatic  nerve  to  touch  the  tongue.  There  is  also  another  remarkable  expe¬ 
riment  of  Aldini,  explicable  on  the  same  principle,  and  shown  in  Fig.  265. 


Fig.  265. — A  Mini’s  Battery , 


Formed  of  the  heads  of  recently  decapitated  oxen,  a,  b,  c. 


One  of  the  ears  of  the  first  head,  A,  is  well  moistened  with  salt  and  water, 
and  connected,  through  the  tongue,  by  a  silver  wire  with  the  ear  of  B ;  the 
tongue  of  B  is  in  like  manner  connected  with  the  ear  of  C. 

The  ear  of  A  and  the  tip  of  the  tongue  of  C  form  the  terminals  of  this 
“bovine  battery;”  silver  wires  brought  round  from  both  are  now  connected 
with  the  prepared  limbs  of  a  frog,  just  killed,  so  that  the  portion  of  the  spine 
still  connected  with  its  lumbar  nerves  touches  the  wire  from  the  tip  of  the 
tongue,  which  had  been  previously  drawn  out  of  the  mouth  of  the  ox,  and 
the  skinned  legs  touch  the  wire  from  one  of  the  ears.  The  frog’s  legs  instantly 
contract,  and  the  contraction  ceases  when  the  circuit  is  broken. 

Dr.  Wilkinson  estimated  that  the  irritable  muscles  of  a  frog’s  leg  were  no 
less  than  56,000  times  more  delicate,  as  a  test  of  electricity,  than  the  most 
sensitive  condensing  electroscope  (p.  243). 

“  About  forty  years  prior  to  Galvani’s  discovery,*  a  person  of  the  name  of 
Sultzer  gave  an  account  of  the  following  fact : 


*  “  Rees’s  Cyclopaedia,”  article  Galvanism. 


VOLTAIC  ELECTRICITY. 


3*9 


“  If  a  piece  of  lead  and  a  similar  piece  of  silver  be  laid  together,  and  the 
edges  of  both  be  brought  in  contact  with  the  tongue,  a  taste  is  perceived  similar 
to  that  of  vitriol  of  iron ;  at  the  same  time  that  the  metals  applied  separately 
produce  no  effect. 

“  The  observer  of  this  fact  does  not  appear  to  have  been  surprised  at  the 
effect.  At  that  time  the  doctrine  of  vibrations  was  employed  to  explain  all 
natural  phenomena. 

“  He,  therefore,  concluded  that  some  peculiar  vibration  took  place  from  the 
contact  of  the  metals,  which  produced  the  peculiar  sensation  on  the  tongue. 

“All  the  world  were  satisfied  with  this  explanation;  and  thus  a  prominent 
fact  had  slept  in  obscurity  from  the  time  of  Sultzer  to  the  time  of  Galvani.” 

The  excitation  of  galvanic  electricity  is  traceable  to  chemical  action.  It  has 
already  been  stated  that  the  combustion  of  a  piece  of  charcoal  will  eliminate 
the  electric  force,  and  can  be  discovered  by  a  delicate  condensing  electro¬ 
scope.  In  galvanic  experiments  another  instrument  is  required,  in  order  to 
detect  the  feeble  currents  of  electricity  of  low  tension  or  intensity. 

This  instrument  admits  of  wonderful  refinement,  as  will  be  seen  presently 
in  the  description  of  Sir  William  Thompson’s  reflecting  galvanometer  needle; 
but  for  ordinary  experiments  an  instrument  constructed  as  follows  will  suffice: 


Fig.  266. —  The  ordinary  Galvanometer  Needle. 

It  will  be  seen  presently,  that  a  single  wire  conveying  an  electric  curren, 
causes  a  magnetic  needle  to  be  deflected,  and  to  take  up  a  position  at  right 
angles  to  the  current.  If  one  wire  can  produce  this  result,  it  is  clear  that, 
by  twisting  the  wire  and  increasing  the  number  of  convolutions,  the  effect  of 
the  single  wire  is  multiplied;  and  by  covering  the  wire  with  s:lk  or  cotton,  so 
as  to  prevent  lateral  communication,  a  much  greater  surface  of  electrified  wire 
is  brought  to  bear  by  induction  upon  the  magnetic  needle.  I  htse  conditions 
are  fulfilled  in  Fig.  266,  which  will  answer  remarkably  well  for  any  ordinary 
lecture-table  experiment:  it  consists  of  a  magnetic  needle,  c,  properly  sus¬ 
pended  and  placed  inside  a  coil  of  wire,  d,  the  two  ends  of  which  terminate 
at  a  b.  The  whole  is  levelled  by  three  screws. 

The  instrument,  Fig.  267,  is  carefully  levelled  by  three  screws  and  spirit- 
levels  ;  it  contains  a  coil  of  fine  wire,  the  two  ends  of  which  are  brought  out 
to  two  screw  connections.  The  magnetic  needle  is  made  astatic  (Jo-ra-ros, 


320 


ELECTRICITY. 


just  balanced),  by  being  connected  with  another  magnetic  needle,  the  north 
pole  of  which  is  placed  opposite  the  south  pole  of  the  other,  and  vice  versd, 
and  is  thus  unaffected  by  the  earth’s  magnetism. 

When  a  current  of  electricity,  however  feeble,  is  passed  through  the  coil, 
the  astatic  needle  is  deflected  according  to  laws  which  will  be  fully  explained 
in  the  article  on  Electro-Magnetism. 


Fig.  267. — The  Galvanometer  Multiplier. 

With  this  instrument  the  following  experiments,  all  demonstrating  that 
chemical  action  is  a  source  of  electricity,  can  be  performed : 

Into  a  small  clean  iron  ladle,  well  scraped  inside  with  a  file  to  secure  a 
metallic  and  not  a  rusted  surface  of  iron,  are  placed  some  crystals  of  nitre;  the 
ladle  is  supported  by  a  tripod  stand  above  a  Bunsen’s  burner,  and,  when 
melted  by  the  heat,  a  wire  is  wound  round  the  clean  metallic  surface  of  the 
handle,  and  connected  with  one  of  the  connecting  screws  of  the  galvanometer, 
and  the  other  with  a  second  wire,  bound  round  a  piece  of  hard  charcoal,  such 
as  would  be  used  for  the  electric  lamp. 

Of  course  all  metallic  connections  must  be  bright  and  clean,  and,  directly 
the  charcoal  is  dipped  into  the  nitre,  the  oxidation  of  the  charcoal  occurs ;  the 
nitre  gives  oxygen  to  the  charcoal,  and  converts  it  into  carbonic  acid,  which 
unites  with  the  remaining  potash,  producing  carbonate  of  potash,  and  at  the 
same  moment  a  current  of  electricity  is  liberated,  which  violently  affects  the 
galvanometer  needle. 

The  writer  gives  a  drawing  of  the  arrangement  which  will  always  be  found 
most  simple  and  effective  at  the  lecture-table.  Moreover,  it  illustrates  another 
fact  that  one  of  the  elements  of  a  voltaic  series  must  be  in  a  liquid  state,  if 
a  notable  current  of  dynamical  electricity  is  desired  to  be  shown  or  used.  The 
writer  has  always  felt  that  when  coal  or  charcoal  could  be  oxidized,  and  used 


VOLTAIC  ELECTRICITY. 


321 


Fig.  268. —  The  Oxidation  of  Carbon, 

An  instance  of  the  evolution  of  electricity  by  true  chemical  action,  a,  iron  ladle,  containing  the 
nitre;  b,  the  charcoal;  c,  the  Bunsen  burner;  d,  the  galvanometer  needle 


in  the  galvanic  battery,  the  cheapest  source  of  electricity  will  have  oeen 
attained  ;  and  he  learns  from  Mr.  Crookes  that  a  plate  of  platinum  and  one  of 
charcoal  placed  in  fused  soda  or  potash  give  a  very  good  current. 

Mr.  Cecil  Wray,  of  Wood  End  House,  Walthamstow,  has  lately  effected 
such  great  improvements  in  the  construction  of  the  thermo  battery,  that  with 
an  ordinary  gas-flame  from  a  Bunsen  burner  he  can  obtain  electric  power 
equal  to  four  or  five  Daniell’s  cells  ;  so  that  coal  gas  or  coke  will  be  essentially 
substituted  for  the  more  expensive  zinc,  described  in  one  edition  of  Walker’s 
English  Dictionary  to  be  “a  kind  of  fossil  substance." 

The  same  experiment  repeated,  and  a  condensing  electroscope  used  as  the 
test  of  electrical  excitation,  with  the  precaution  of  supporting  the  charcoal  on 
a  glass  rod,  is  very  satisfactory;  and  thus  by  the  oxidation  and  slow  burning 
of  charcoal,  both  current  or  dynamical  electricity  and  static  electricity  may  be 
obtained. 

The  usual  mode  of  showing  that  charcoal  ih  a  state  of  combustion  elimi¬ 
nates  electricity  is  by  twisting  a  piece  of  copper  wire  round  a  bit  of  charcoal 
some  inches  in  length,  and  then  connecting  it  with  the  lower  plate  of  the  con¬ 
densing  electroscope,  whilst  the  upper  plate  is  connected  with  the  ground. 

The  charcoal  is  now  ignited  by  a  spirit-lamp,  and  if  blown  on  with  bellows, 
and  the  top  plate  of  the  electroscope  raised  and  lowered  several  times,  any 
rubbing  of  tlie  two  plates  one  against  the  other  being  carefully  avoided,  the 
gold  leaves  will  be  seen  to  diverge  with  negative  electricity  ;  and  sometimes 
one  movement  of  the  upper  plate  of  the  condensing  electroscope  is  found  to 
be  sufficient. 

The  experiments  already  quoted  form  a  sort  of  connecting-link  between 
frictional  and  voltaic  electricity,  and  are  further  supported  by  some  excellent 
experiments  of  Faraday,  who  shows  by  a  simple  arrangement  that  the  elcctri- 

21 


322 


ELECTRICITY. 


city  of  high  tension  obtained  from  the  electrical  machine  will  do  all  that  a 
voltaic  circuit  may  effect.  Faraday  says  :* 

“  Chemical  Decomposition. — The  chemical  action  of  voltaic  electricity  is 
characteristic  of  that  agent,  but  not  more  characteristic  than  are  the  laws 
under  which  the  bodies  evolved  by  decomposition  arrange  themselves  at  the 
poles.  Dr.  Wollaston  showed  f  that  common  electricity  resembled  it  in  these 
effects,  and  that  ‘they  are  both  essentially  the  same;’  but  he  mingled  with 
his  proofs  an  experiment  having  a  resemblance,  and  nothing  more,  to  a  case 
of  voltaic  decomposition,  which,  however,  he  himself  partly  distinguished  ; 
and  this  has  been  more  frequently  referred  to  by  others,  on  the  one  hand,  to 
prove  the  occurrence  of  electro-chemical  decomposition,  like  that  of  the  pile, 
and,  on  the  other,  to  throw  doubt  upon  the  whole  paper,  than  the  more  nume¬ 
rous  and  decisive  experiments  which  he  has  detailed. 

“  I  take  the  liberty  of  describing  briefly  my  results,  and  of  thus  adding  my 
testimony  to  that  of  Dr.  Wollaston  on  the  identity  of  voltaic  and  common 
electricity  as  to  chemical  action,  not  only  that  I  may  facilitate  the  repetition 
of  the  experiments,  but  also  lead  to  some  new  consequences  respecting  electro¬ 
chemical  decomposition. 

“1  first  repeated  Wollaston’s  fourth  expedment.*  in  which  the  ends  of 
coated  silver  wires  are  immersed  in  a  drop  of  sulphate  of  copper.  By  passing 
the  electricity  of  the  machine  through  such  an  arrangement,  that  end  in  the 
drop  which  received  the  electricity  became  coated  with  metallic  copper.  One 
hundred  turns  of  the  machine  produced  an  evident  effect ;  two  hundred  turns 
a  very  sensible  one.  'I  he  decomposing  action  was,  however,  very  feeble.  Very 
little  copper  was  precipitated,  and  na  sensible  trace  of  silver  from  the  other 
pole  appeared  in  the  solution. 


Fig.  269. 


“  A  much  more  convenient  and  effectual  arrangement  for  chemical  decompo¬ 
sitions  by  common  electricity  is  the  following  : 

“  Upon  a  glass  plate  (Fig.  269)  placed  over,  but  raised  above,  a  piece  of 
white  paper — so  that  shadows  may  not  interfere — put  two  pieces  of  tinfoil,  a,  b j 


*  “  Experimental  Researches  in  Electricity,”  by  Michael  Faraday, 
t  “  Philosophical  Transactions,”  1801,  pp.  427,  434.  J  Ibid.,  1801,  p.  429. 


VOLTAIC  ELECTRICITY. 


323 


connect  one  of  these  by  an  insulated  wire  <r,  or  wire  and  string,  with  the 
machine,  and  the  other,  g,  with  the  discharging  train,  or  the  negative  con¬ 
ductor  ;  produce  two  pieces  of  fine  platina  wire,  bent  as  in  Fig.  270,  so  that 
the  part  d  f  shall  be  nearly  upright,  whilst  the  whole  is  resting  on  the  three 
bearing  points,  p ,  e.  f ;  place  these  as  in  Fig.  269  ;  the  points  /,  «,  then  become 
the  decomposing  poles.  In  this  way  services  of  contact,  as  minute  as  possible, 
can  be  obtained  at  pleasure,  and  the  connection  can  be  broken  or  renewed 

in  a  moment,  and  the  substances  acted  upon 
examined  with  the  utmost  facility. 

“  A  coarse  line  was  made  on  the  glass  with 
solution  of  sulphate  of  copper,  and  the  termina¬ 
tions  p  and  n  put  into  it ;  the  foil,  was  con¬ 
nected  with  the  positive  conductor  of  the  machine 
by  wire  and  wet  string,  so  that  no  sparks  passed  ; 
twenty  turns  of  the  machine  caused  the  pre¬ 
cipitation  of  so  much  copper  on  the  end,  p ,  that 
it  looked  like  copper  wire  ;  no  apparent  change 
took  place  at  n. 

“  A  mixture  of  half  muriatic  acid  and  half  water  was  rendered  deep  blue  by 
sulphate  of  indigo,  and  a  large  drop  put  on  the  glass  (Fig.  269),  so  that  p  and 
11  were  immersed  at  opposite  sides ;  a  single  turn  of  the  machine  showed 
bleaching  effects  round  p ,  from  evolved  chlorine.  After  twenty  revolutions  no 
effect  of  the  kind  was  visible  at  n ;  but  so  much  chlorine  had  been  set  free  at  p, 
that  when  the  drop  was  stirred  the  whole  became  colourless. 

“  A  drop  of  solution  of  iodide  of  potassium  mingled  with  starch  was  put 
into  the  same  position  at  p  and  nj  on  turning  the  machine,  iodine  was  evolved 
at  p ,  but  not  at  n. 

“A  still  further  improvement  in  this  form  of  apparatus  consists  in  wetting 
a  piece  of  filtering  paper  in  the  solution  to  be  experimented  on,  and  placing 
that  under  the  points  p  and  n,  on  the  glass ;  the  paper  retains  the  substance 
evolved  at  the  point  of  evolution,  by  its  whiteness  renders  any  change  of 
colour  visible,  and  allows  of  the  point  of  contact  between  it  and  the  decom¬ 
posing  wares  being  contracted  to  the  utmost  degree.  A  piece  of  paper 
moistened  in  the  solution  of  iodide  of  potassium  and  starch,  or  of  the  iodide 
alone,  with  certain  precautions,  is  a  moct  admirable  test  of  electro-chemical 
action,  and,  when  thus  placed  and  acted  upon  by  the  electric  current,  will 
show  iodine  evolved  at  p  by  only  half  a  turn  of  the  machine.  With  these 
adjustments,  and  the  use  of  iodide  of  potassium  on  paper,  chemical  action  is 
sometimes  a  more  delicate  test  of  electrical  currents  than  the  galvanometer. 
Such  cases  occur  when  the  bodies  traversed  by  the  current  are  bad  conductors, 
or  when  the  quantity  of  electricity  evolved  or  transmitted  in  a  given  time  is 
very  small. 

“A  piece  of  litmus  paper,  moistened  in  solution  of  common  salt  or  sulphate 
of  soda,  was  quickly  reddened  at  p.  A  similar  piece,  moistened  in  muriatic 
acid,  was  very  soon  bleached  at  p.  No  effects  of  a  similar  kind  took  place  at  n. 

“A  piece  of  turmeric  paper,  moistened  in  solution  of  sulphate  of  soda,  was 
reddened  at  n  by  two  or  three  turns  of  the  machine,  and  in  twenty  or  thirty 
turns  plenty  of  alkali  was  there  evolved.  On  turning  the  paper  round,  so  that 
the  spot  came  under  p,  and  then  working  the  machine,  the  alkali  soon  dis¬ 
appeared,  the  place  became  yellow,  and  a  brown  alkaline  spot  appeared  in  the 
new  part  under  n. 

21 — 2 


324 


ELECTRICITY. 


“On  combining  a  piece  of  litmus  with  a  piece  of  turmeric  paper,  wetting 
both  with  solution  of  sulphate  of  soda,  and  putting  the  paper  on  the  glass,  so 
that  p  was  on  the  litmus  and  n  on  the  turmeric,  a  very  few  turns  of  the 
machine  sufficed  to  show  the  evolution  of  acid  at  the  former,  and  alkali  at  the 
latter,  exactly  in  the  manner  effected  by  a  volta-electric  current. 

“  All  these  decompositions  took  place  equally  well,  whether  the  electricity 
passed  from  the  machine  to  the  foil,  a ,  through  water  or  through  wire  only, 
by  contact  with  the  conductor  or  by  sparks  there,  provided  the  sparks  were 
not  so  large  as  to  cause  the  electricity  to  pass  in  sparks  from  p  to  «,  or  towards 
n;  and  I  have  seen  no  reason  to  believe  that,  in  cases  of  true  electro-chemical 
decomposition  by  the  machine,  the  electricity  passed  in  sparks  from  the  con 
ductor,  or  at  any  part  of  the  current,  is  able  to  do  more,  because  of  its  tension, 
than  that  which  is  made  to  pass  merely  as  a  regular  current. 

“  Finally,  the  experiment  was  extended  into  the  following  form,  supplying 
in  this  case  the  fullest  analogy  between  common  and  voltaic  electricity: 


“Three  compound  pieces  of  litmus  and  turmeric  paper  were  moistened  in 
solution  of  sulphate  of  soda,  and  arranged  on  a  plate  of  glass  with  platina 
wires,  as  in  Fig.  271.  The  wire,  in ,  was  connected  with  the  prime  conductor 
of  the  machine,  the  wire,  t ,  with  the  discharging  train,  and  the  wires,  r  and 
s,  entered  into  the  course  of  the  electrical  current  by  means  of  the  pieces  of 
moistened  paper ;  they  were  so  bent  as  to  rest  each  on  three  points,  11,  r,  p , 
ni  si  P-,  the  points,  r  and  s,  being  supported  by  the  glass,  and  the  others  by  the 
papers ;  the  three  terminations,  /,  /,  p ,  rested  on  the  litmus,  and  the  other 
three,  «,  n,  n,  on  the  turmeric  paper.  On  working  the  machine  for  a  short 
time  only,  acid  was  evolved  at  all  the  poles  or  terminations,/,/,  /,  by  which 
the  electricity  entered  the  solution,  an  ’  alkali  at  the  other  poles,  n,  11 ,  n,  by 
which  the  electricity  left  the  solution. 

u  I'1  experiments  of  electro-chemical  decomposition  by  the  common 
machine  and  moistened  papers,  it  is  necessary  to  be  aware  of  and  to  avoid 
the  following  important  source  of  error: 

If  a  spark  passes  over  moistened  litmus  and  turmeric  paper,  the  litmus 
paper  (provided  it  be  delicate,  and  not  too  alkaline)  is  reddened  by  it ;  and  if 
several  sparks  are  passed,  it  becomes  powerfully  reddened.  If  the  electricity 
pass  a  little  way  from  the  wire  over  the  surface  of  the  moistened  paper,  before 
it  finds  mass  and  moisture  enough  to  conduct  it,  then  the  reddening  extends 
as  fai  as  the  ramifications.  If  similar  ramifications  occur  at  the  termination 
11,  on  the  turmeric  paper,  they  prevent  the  occurrence  of  the  red  spot  due  to 


VOLTAIC  ELECTRICITY. 


325 

the  alkali,  which  would  otherwise  collect  there  ;  sparks  or  ramifications  from 
the  points,  //,  will  also  redden  litmus  paper.  If  paper,  moistened  by  a  solution 
of  iodide  of  potassium  (which  is  an  admirably  delicate  test  of  electro-chemical 
action),  be  exposed  to  the  sparks  or  ramifications,  or  even  a  feeble  stream  of 
electricity  through  the  air  from  either  the  point  p  or  n,  iodine  will  be  immedi¬ 
ately  evolved. 

“  These  effects  must  not  be  confounded  with  those  due  to  the  true  electro¬ 
chemical  powers  of  common  electricity,  and  must  be  carefully  avoided  when 
the  latter  are  to  be  observed.  No  sparks  should  be  passed,  therefore,  in  any 
part  of  the  current,  nor  any  increase  of  intensity  allowed  by  which  the  elec¬ 
tricity  may  be  induced  to  pass  between  the  platina  wires  and  the  moistened 
papers,  otherwise  than  by  conduction ;  for,  if  it  burst  through  the  air,  the 
eflect  referred  to  ensues. 

“  The  effect  itself  is  due  to  the  formation  of  nitric  acid  by  the  combination 
of  the  oxygen  and  nitrogen  of  the  air,  and  is,  in  fact,  only  a  delicate  repetition 
of  Cavendish’s  beautiful  experiment.  The  acid  so  formed,  through  small  in 
quantity,  is  in  a  high  state  of  concentration  as  to  water,  and  produces  the 
consequent  effects  of  reddening  the  litmus  paper,  or  preventing  the  exhibition 
of  alkali  on  the  turmeric  paper,  or,  by  acting  on  the  iodide  of  potassium, 
evolving  iodine. 

“  By  moistening  a  very  small  slip  of  litmus  paper  in  solution  of  caustic 
potassa,  and  then  passing  the  electric  spark  over  its  length  in  the  air,  I  gradu¬ 
ally  neutralized  the  alkali,  and  ultimately  rendered*  the  paper  red;  on  drying 
it,  I  found  that  nitrate  of  potassa  had  resulted  from  the  operation,  and  that 
the  paper  had  become  touch-paper. 

“  Either  litmus  paper  or  white  paper  moistened  in  solution  of  iodide  of 
potassium  offers,  therefore,  a  very  simple,  beautiful,  and  ready  means  of  illus¬ 
trating  Cavendish’s  experiment  of  the  formation  of  nitric  acid  from  the 
atmosphere. 

“  I  have  already  had  occasion  to  refer  to  an  experiment  by  Dr.  Wollaston, 
which  is  insisted  upon  too  much,  both  by  those  who  oppose  and  those  who 
agree  with  the  accuracy  of  his  views  respecting  the  identity  of  voltaic  and 
ordinary  electricity.  By  covering  fine  wires  with  glass  or  other  insulating 
substances,  and  then  removingonly  so  much  matter  as  to  expose  the  point 
or  a  section  of  the  wires,  and  by  passing  electricity  through  two  such  wires, 
the  guarded  points  of  which  were  immersed  in  water,  Wollaston  found  that 
the  water  could  be  decomposed  even  by  the  current  from  the  machine,  without 
sparks,  and  that  two  streams  of  gas  arose  from  the  points,  exactly  resembling 
in  appearance  those  produced  by  voltaic  electricity,  and,  like  the  latter,  giving 
a  mixture  of  oxygen  and  hydrogen  gases.  But  Dr.  Wollaston  himself  points 
out  that  the  effect  is  different  from  that  of  the  voltaic  pile,  inasmuch  as  both 
oxygen  and  hydrogen  are  evolved  from  each  pole ;  he  calls  it  ‘  a  very  close 
imitation  of  the  galvanic  phenomena,’ but  adds,  that  ‘in  fact  the  resemblance 
is  not  complete,’  and  docs  not  trust  to  it  to  establish  the  principles  correctly 
laid  down  in  his  paper. 

“  This  experiment  is  neither  more  nor  less  than  a  repetition,  in  a  refined 
manner,  of  that  made  by  Dr.  Pearson,  in  179 7,*  and  previously  by  MM. 
Pacts  van  Troostwyk  and  Dciman  in  1789,  or  earlier.  That  the  experiment 
should  never  be  quoted  as  proving  true  electro-chemical  decomposition  is 


*  "Nicholson's  Journal,’’  .jto,  vol.  i.,  pp.  J41,  299,  349- 


326 


ELECTRICITY. 


sufficiently  evident  from  the  circumstance,  that  the  law  which  regulates  the 
transference  and  final  place  of  the  evolved  bodies  has  no  influence  here.  The 
water  is  decomposed  at  both  poles  independently  of  each  other,  and  the  oxygen 
and  hydrogen  evolved  at  the  wires  are  the  elements  of  the  water  existing  the 
instant  before  in  those  places.  That  the  poles,  or  rather  points,  have  no  mutual 
decomposing  dependence  may  be  shown  by  substituting  a  wire,  or  the  finger, 
for  one  of  them,  a  change  which  does  not  at  all  interfere  with  the  other,  though 
it  stops  all  action  at  the  changed  pole.  This  fact  may  be  observed  by  turning 
the  machine  for  some  time ;  for,  though  bubbles  will  rise  from  the  point  left 
unaltered,  in  quantity  sufficient  to  cover  entirely  the  wire  used  for  the  other 
communication,  if  they  could  be  applied  to  it,  yet  not  a  single  bubble  will 
appear  on  that  wire. 

“When  electro-chemical  decomposition  takes  place,  there  is  great  reason  to 
believe  that  the  quantity  of  matter  decomposed  is  not  proportionate  to  the 
intensity,  but  to  the  quantity  of  electricity  passed.  Of  this  I  shall  be  able  to 
offer  some  proofs  in  a  future  part  of  this  paper.  But  in  the  experiment  under 
consideration  this  is  not  the  case.  If,  with  a  constant  pair  of  points,  the  elec¬ 
tricity  be  passed  from  the  machine  in  sparks,  a  certain  proportion  of  gas  is 
evolved;  but,  if  the  sparks  be  rendered  shorter,  less  gas  is  evolved;  and  if  no 
sparks  be  passed,  there  is  scarcely  a  sensible  portion  of  gases  set  free.  On 
substituting  solution  of  sulphate  of  soda  for  water,  scarcely  a  sensible  quantity 
of  gas  could  be  procured  even  with  powerful  sparks,  and  almost  none  with  the 
mere  current;  yet  the  quantity  of  electricity  in  a  given  time  was  the  same  in 
all  these  cases. 

“  I  do  not  intend  to  .deny  that  with  such  an  apparatus  common  electricity 
can  decompose  water  in  a  manner  analogous  to  that  of  the  voltaic  pile;  I  be¬ 
lieve  at  present  that  it  can.  But  when  what  I  consider  the  true  effect  only 
was  obtained,  the  quantity  of  gas  given  off  was  so  small  that  I  could  not  ascer¬ 
tain  whether  it  was,  as  it  ought  to  be,  oxygen  at  one  wire  and  hydrogen  at 
the  other.  Of  the  two  streams  one  seemed  more  copious  than  the  other,  and 
on  turning  the  apparatus  round,  still  the  same  side  in  relation  to  the  machine 
gave  the  largest  stream.  On  substituting  solution  of  sulphate  of  soda  for  pure 
water,  these  minute  streams  were  still  observed;  but  the  quantities  were  so 
small  that  on  working  the  machine  for  half  an  hour  I  could  not  obtain  at  either 
pole  a  bubble  of  gas  larger  than  a  small  grain  of  sand.  If  the  conclusion 
which  I  have  drawn  relating  to  the  amount  of  chemical  action  be  correct,  this 
ought  to  be  the  case. 

“  I  have  been  the  more  anxious  to  assign  the  true  value  of  this  experiment 
as  a  test  of  electro-chemical  action,  because  I  shall  have  occasion  to  refer  to 
it  in  cases  of  supposed  chemical  action  by  magneto-electric  and  other  electric 
currents  and  elsewhere.  But,  independent  of ‘it,  there  cannot  be  now  a  doubt 
that  Dr.  Wollaston  was  right  in  his  general  conclusion,  and  that  voltaic  and 
common  electricity  have  powers  of  chemical  decomposition  alike  in  their 
nature  and  governed  by  the  same  law  of  arrangement. 

'‘‘Physiological  Effects.  —  The  power  of  the  common  electric  current  to  shock 
and  convulse  the  animal  system,  and  when  weak  to  affect  the  tongue  and  the 
eyes,  may  be  considered  as  the  same  with  the  similar  power  of  voltaic  elec¬ 
tricity,  account  being  taken  of  the  intensity  of  the  one  electricity  and  duration 
of  the  other.  When  a  wet  thread  was  interposed  in  the  course  of  the  current  of 
common  electricity  from  the  battery  charged  by  eight  or  ten  revolutions  of 
the  machine  in  good  action,  and  the  discharge  made  by  platina  spatulas 


VOLTAIC  ELECTRICITY. 


32  7 


through  the  tongue  or  the  gums,  the  effect  upon  the  tongue  and  eyes  was 
exactly  that  of  a  feeble  voltaic  circuit. 

“Spark. — The  beautiful  flash  of  light  attending  the  discharge  of  common 
electricity  is  well  known.  It  rivals  in  brilliancy,  if  it  does  not  even  very  much 
surpass,  the  light  from  the  discharge  of  voltaic  electricity;  but  it  endures  for 
an  instant  only,  and  is  attended  by  a  sharp  noise  like  that  of  a  small  explosion. 
Still  no  difficulty  can  arise  in  recognizing  it  to  be  the  same  spark  as  that  from 
the  voltaic  battery,  especially  under  certain  circumstances.  The  eye  cannot 
distinguish  the  difference  between  a  voltaic  and  a  common  electricity  spark,  if 
they  be  taken  between  amalgamated  surfaces  of  metal,  at  intervals  only,  and 
through  the  same  distance  of  air.” 

The  simple  voltaic  circuit  may  be  variously  modified,  but  usually  consists 
of  three  elements,  viz.,  two  solids  and  one  fluid,  or  one  solid  and  two  fluids. 
The  first  is  well  represented  by  a  plate  of  copper,  a  plate  of  zinc,  and  some 
water  acidulated  with  sulphuric  acid  ;  the  second  by  a  single  plate  of  zinc,  one 
half  of  which  is  immersed  in  salt  and  water,  and  the  other  in  weak  nitric  acid. 


FlG.  272. — A  simple  Voltaic  Circuit ,  consisting  of  two  Metals  anti  one  Fluid. 

a.  zinc;  b,  copper.  The  liquid  represents  the  acid,  and  the  arrows  show  the  direction  of  the  current. 


In  the  above  figure  it  is  seen  that  the  zinc  fulfils  the  part  of  the  glass  in  the 
electrical  machine;  the  acid,  the  rubber  or  excitant;  the  copper,  the  con- 


Fig.  273. — Magnetic  Needle ,  suspended  over  two  Plates  which  are  immersed 

in  acid  and  water. 


328 


ELECTRICITY. 


ductor.  By  using  a  galvanometer,  it  is  found  that  a  current  of  +  electricity 
flows  from  the  zinc  to  the  copper;  and  when  the  wires  attached  to  the  plates 
are  brought  in  contact,  this  is  called  a  closed  circuit. 

Every  part  of  the  circuit  exercises  an  influence  upon  the  magnetic  needle. 

If  a  needle  is  suspended  over  the  two  plates  (Fig.  273)  lying  in  any  convenient 
glass  or  porcelain  dish,  the  needle,  which  should  be  arranged  so  that  its  direction 
is  at  right  angles  to  the  immersed  plates,  is  then  deflected  parallel  with  them. 

If  we  take  one  cell  of  a  Cruikshank  battery,  we  find  a  plate  of  zinc  soldered 
to  one  of  copper,  these  compound  plates  forming  the  sides  of  the  cell,  in  which 
dilute  acid  is  poured. 


\v 


z,  c,  zinc  and  copper,  soldtred  together  and  cemented  into  a  trough,  a  a.  The  current  does  not  pass  until 
a  bent  wive,  w,  connects  the  two  sides  containing  the  dilute  sulphuric  acid 


In  Volta's  crown  of  cups  a  simple  voltaic  circuit,  formed  of  slips  of  zinc  and 
copper,  soldered  together  and  placed  alternately  in  separate  glass  vessels, 
represents  another  arrangement  for  producing  the  same  result. 


A  \  a,  the  tr  ugh,  divided  by  a  water-tight  partition  ;  z,  the  zinc  plate;  c,  the  copper  plate  The  cur¬ 
rent  c  rculates  in  the  direction  of  the  arrows  when  the  wire,  w  w  w  w.  is  bent  over  and  dips  into  the 
dilute  acid 

A  plate  of  zinc,  inserted  water-tight  into  a  wooden  trough,  usually  lined  with 


VOLTAIC  ELECTRICITY. 


329 


a  cement  made  of  rosin  and  tallow,  filled  on  one  side  with  a  solution  of  common 
salt,  and  on  the  other  with  dilute  nitric  .acid,  gives  a  current  if  two  wires  are 
inserted  on  either  side,  but  not  touching  the  metal 


F IG.  276.  —Zinc  Plate ,  cemented  into  a  Mahogany  Trough. 

The  arrows  show  the  direction  of  the  current. 


Or  the  arrangement  may  be  varied  by  placing  a  long  strip  of  clean  copper  in 
a  cylindrical  glass  (Fig.  277) ;  into  this  is  poured  dilute  nitric  acid  until  half  the 
vessel  is  filled;  then,  with  a  tube  and  funnel,  a  strong  solution  of  sulphate  of 
copper  is  poured  down  to  the  bottom  of  the  glass,  which,  gravitating  by  its 
weight,  raises  the  weak  nitric  acid  above  it,  and  thus  the  copper  is  immersed 
in  two  solutions,  the  shaded  one,  A,  being  the  solution  of  copper,  and  the  one 
above  it,  B,  the  dilute  nitric  acid. 

A  wire,  G,  covered  with  gutta  percha,  but  exposing  an  inch  or  two  of  the 
rim,  is  now  let  down  quickly  into  the  glass  vessel,  so  that  the  gutta-percha 
covered  portion  passes  through  the  upper  stratum,  and  the  exposed  wire  only 
is  in  contact  with  the  solution  of  sulphate  of  copper. 

An  uncovered  copper  wire,  H,  is  put  into  the  dilute  nitric  acid;  and  when 
the  ends  of  the  two  wires,  G  and  H,  are  brought  into  metallic  contact,  a  cur¬ 
rent  circulates  in  the  direction  of  the  arrows,  and  for  every  atom  of  copper 
dissolved  in  It  an  equivalent  proportion  of  the  metal  is  deposited  out  of  a  on 
to  the  lower  part  of  the  copper  plate,  C  C. 

Professor  Matteucci,  of  Pisa,  has  shown  that  dissected  legs  of  frogs,  so 
arranged  that  the  half-thighs,  skinned  and  laid  alternately  upon  each  other, 
the  inner  half  touching  the  outer,  and  vice  versa ,  produce  a  current  of  elec¬ 
tricity  with  which  all  the  ordinary  effects  are  produced,  viz.,  deflection  of 
galvanometer,  decomposition  of  iodide  of  potassium,  and  divergence  of  the 
gold  leaves  of  an  electroscope.  The  electricity  is  that  which  belongs  to  the 
animal,  and,  as  proved  by  Matteucci,  circulates  from  the  interior  to  the  exterior 
of  the  muscle.  He  found  that  -f-  electricity  always  circulates  from  the  inside 
to  the  outside  of  the  muscles  of  all  animals,  whether  of  birds,  mammals, 
fishes,  or  cold-blooded  reptiles.*  Thus  it  is  shown  that  metals  may  be  dis- 


*  Matteucci  has  suggested  that  the  true  muscular  fibre,  which  is  oxidized,  represents  the  zinc;  the 
sarcoltmma  of  the  animal  body,  the  platinum ;  whilst  the  exciting  fluid  is  the  blood. 


33° 


ELECTRICITY. 


Fig.  277. 

pensed  with,  and  the  exclamation  ascribed  to  Napoleon  I.,  by  Chaptal,  whilst 
looking  at  the  action  and  power  of  his  voltaic  battery,  derives  additional  force 
on  reviewing  the  last-named  fact.  The  remark  of  the  august  man  was  this: 

“  Voilk,  docteur,  l’image  de  la  vie:  la  colonne  vertebrale  est  le  pile,  la  vessie 
le  pole  positif,  et  le  foie  le  pole  negatif.” 

Sir  H.  Davy  endeavoured  to  protect  the  copper  sheathing  of  vessels  by 
attaching  a  metal  which  was  more  rapidly  oxidized  than  the  copper.  His  ex¬ 
periments  appeared  at  first  to  be  thoroughly  successful,  a  bit  of  zinc  as  large  as 


Fig.  278. — Original  Experiments  of  Sir  H.  Davy , 

Given  to  the  late  Professor  Griffith  by  Davy,  and  passing  to  the  writei,  being  pieces  of  copper  and  their 
proiectors,  arranged  by  Sir  Humphrey  Davy’s  own  hands  in  his  first  experiments  on  the  protection  of 

copper  sheathing. 


a  small-bore  bullet  being  sufficient  to  protect  a  surface  of  copper  40  or  50  inches 
square;  indeed,  it  may  be  said  that  Davy’s  experiments  were  too  successful, 
for  directly  the  action  of  the  chlorides  in  the  sea-water  was  stopped,  and  the 


VOLTAIC  ELECTRICITY. 


33i 


poisonous  salt  of  copper  no  longer  produced,  the  living  things — the  barnacles, 
the  sea-weed,  &c. — attached  themselves,  like  Sinbad  to  the  floating  island, 
and,  whilst  making  themselves  uninvited  passengers,  they  impeded  the  motion 
of  the  vessel  by  fouling  its  coppered  sides. 

The  drawing,  Fig.  278,  represents  the  actual  slips  of  copper,  w'ith  bits  of  zinc 
tied  round  them  with  silk,  used  by  Sir  H.  Davy  in  his  first  experiments. 

The  principle  of’ the  action  of  the  simple  voltaic  circle — zinc,  copper,  acid 
— is  the  use  of  dissimilar  metals,  one  being  acted  upon  more  than  the  other. 

The  principle  is  so  true,  that  a  current  may  be  obtained  from  two  plates 
of  zinc,  provided  they  differ  in  their  mechanical  or  chemical  state.  By 
melting  zinc  repeatedly  and  pouring  it  into  cold  water,  a  metal  is  obtained 
which  is  remarkably  pure,  and  upon  w'hich  dilute  sulphuric  acid  acts  very 
feebly. 

If  now  a  plate  of  this  pure  metal  is  made  the  opposite  one  to  another  of 
ordinary  zinc,  and  the  two  connected  with  wires,  a  current  is  obtained,  which 
distinctly  deflects  the  galvanometer  needle. 

The  writer,  whilst  making  a  great  number  of  experiments  on  the  probable 
effect  of  the  water  contained  in  the  various  docks  on  the  copper  sheathing  of 
vessels,  found  that  the  plates  of  the  sheathing  lost  weight,  whilst  the  nail 
increased  in  weight  in  the  exact  proportion  lost  by  the  sheathing — as  if  the 
soft  copper  sheathing  became  the  zinc  element,  and  the  harder  pure  copper 
nails  the  copper  element. 

The  experiments  were  twenty  in  number,  a  bit  of  sheathing  and  a  nail  in¬ 
serted  through  a  hole  in  the  metal  being  suspended  by  a  silk  thread  in  twenty 
different  samples  of  London  water.  With  hardly  one  exception,  the  sheathing 
lost  weight,  which  the  nad  gained. 

The  writer’s  experiment  with  fused  nitre  and  charcoal  (p.  291)  demonstrates 
that  water  can  be  entirely  dispensed  with,  thus  proving,  as  in  Matteucci’s  ex¬ 
periments,  that  metals  arc  not  absolutely  necessary.  Fluidity  of  some  kind 
is,  however,  indispensable  to  the  production  of  current  or  dynamical  electricity ; 
and  this  fact  conducts  us  to  an  assemblage  of  simple  voltaic  circles,  or  v^hat 
is  termed  a  voltaic  pile  or  battery. 

In  1819  a  writer  on  Voltaism  says: 

“In  the  galvanic  battery  there  appear  to  be  two  sources  from  which  the 
electricity  is  obtained.  The  one  is  that  which  arises 
from  the  contact  of  the  metals,  and  the  other  from  the 
chemical  action  between  the  interposing  fluid  and  the 
zinc  surface.  The  first  does  not  require  even  the  pre¬ 
sence  of  moisture,  as  is  shown  in  the  electric  column  of 
De  Luc.  The  second  is  rendered  greatly  conspicuous 
by  introducing  between  the  opposite  surfaces  any  sub¬ 
stance  capable  of  oxidating  and  dissolving  the  zinc.” 

It  is  well  to  mention  here  that  Faraday  has  shoum, 
by  one  of  his  simple  and  original  experiments,  that  an 
electric  current  can  be  set  up  independent  of  all  con¬ 
tact. 

It  consists  of  a  piece  of  zinc,  b ,  bent  as  in  the  figure, 
and  a  plate  of  platinum,  a ,  to  which  is  soldered  a  pla¬ 
tinum  wire.  A  little  piece  of  bibulous  paper  is  moistened 
with  a  solution  of  iodide  of  potassium  and  starch,  and 
laid  upon  b.  When  the  two  metais  are  placed  in 


Fig.  279. 


ELECTRICITY. 


33  2 


the  glass  vessel  containing  diluted  sulphuric  acid,  and  the  end  of  the  wire 
pressed  upon  it,  iodine  is  liberated,  which,  uniting  with  the  starch,  produces 
a  purple  compound  ;  and  thus  proves  satisfactorily  that  a  current  of  electricity 
has  passed  through  the  salt,  and  that  true  electro-chemical  decomposition  has 
taken  place. 

“  Acids  are  the  great  promoters  of  the  energy  afforded  by  chemical  action, 
because  they  dissolve  the  zinc  after  it  has  been  oxidated  by  the  oxygen  of  the 
water. 

“  This  is  more  especially  the  case  with  the  sulphuric  and  muriatic  acids, 
because  these  acids  are  not  decomposed  by  the  zinc. 

“  The  nitric  acid  produces  a  still  greater  galvanic  effect,  because  the  acid  is 
decomposed  and  oxidates  the  zinc  with  greater  facility  than  water. 

“The  water  is  also  decomposed  when  this  acid  is  used,  and  hydrogen  is 
always  evolved.” 

These  views  of  the  rationale  of  the  action  of  the  acids  in  the  voltaic  bat¬ 
tery  are  substantially  correct,  although  written  forty-eight  years  ago. 

The  same  writer*  anticipates  the  porous  material  required  in  Daniell’s  and 
Grove’s  batteries ;  and,  indeed,  the  more  frequently,  we  consult  old  works,  the 
more  difficult  do  we  find  it  to  disprove  the  words  of  Solomon,  “There  is 
nothing  new  under  the  sun.”  The  writer  remarks  : 

“When  the  fluids  are  required  to  be  strictly  separate,  a  bladder  answers 
very  well  as  a  separating  medium.  Animal  and  vegetable  substances,  how¬ 
ever,  abound  with  so  many  elements  that  in  nice  experiments  they  would  be 
objectionable.  A  vessel,  divided  into  a  proper  number  of  cells,  of  earthen¬ 
ware ,  in  the  state  of  biscuit ,  would  be  best  calculated  for  these  experiments. 

“  This  vessel  should  be  made  of  pure  silex  and  pure  alumina. 

“  Should  it  ever  become  an  object  of  manufacture  to  separate  acids  and 
alkalies  from  neutral  salts,  a  vessel  of  wood,  with  a  separation  in  the  middle 
of  unglazed  earthenware ,  would  answer  very  well.” 

Here  we  have  porous  cells  anticipated  distinctly. 

The  important  discovery  of  accumulating  the  effects  of  single  voltaic  circles 
was  made  by  Volta  in  1800,  and  the  first  apparatus  constructed  with  that  view 
was  called  the  voltaic  pile. 

The  apparatus  as  first  made  by  Volta  (Fig.  280)  consisted  of  a  certain  number 
of  pairs  of  zinc  and  silver  plates,  separated  from  each  other  by  pieces  of  wet 
cloth.  Hence  the  arrangement  was  as  follows:  —  zinc,  silver,  and  wet  cloth; 
zinc,  silver,  wet  cloth,  and  so  on.  The  silver  plates  were  chiefly  silver  coins, 
the  plates  of  zinc  and  the  pieces  of  cloth  being  of  the  same  size.  He  found 
this  pile  much  more  powerful  when  the  pieces  of  cloth  were  moistened  with  a 
solution  of  common  salt  instead  of  pure  water.  A  pile  consisting  of  forty  pairs 
of  plates  he  found  to  possess  the  power  of  giving  a  very  smart  shock  similar 
to  that  of  an  electric  jar,  and  that  this  effect  took  place  as  often  as  a  commu¬ 
nication  was  made  between  each  end  of  the  pile,  and  as  long  as  the  pieces 
of  cloth  remained  moist.  An  account  of  this  discovery  was  communicated  to 
the  Royal  Society,  and  published  in  the  “Philosophical  Transactions.” 

We  do  not  hear  of  this  celebrated  philosopher  making  any  further  discovery 
after  the  invention  of  the  pile  and  ascertaining  the  nature  and  extent  of  its 
effect  upon  animals. 

Mr.  Cruikshank  improved  upon  Volta’s  apparatus  by  cementing  the  plates 


*  “Rees’s  Cyclopaedia,”  article  Voltaism. 


VOLTAIC  ELECTRICITY. 


333 


Fig.  280. — The  Voltaic  Pile. 


of  zinc  and  copper  into  a  wooden  box,  which  was  then  called  the  galvanic 
trough.  In  fact,  the  trough  was  Volta’s  pile  placed  horizontally,  the  cells 
being  for  the  reception  of  the  fluid  to  answer  the  purpose  of  pieces  of  wet 

cloth. 


Fig.  281. — Babington's  improved  Volta’s  “  Couronne  de  Passes.” 

The  places  lift  in  and  out  of  the  acid. 


The  learned  Dr.  Wollaston  improved  upon  Cruikshank’s  arrangement  by 
increasing  the  area  of  the  conducting  clement,  viz.,  the  copper,  by  doubling 
this  over  the  zinc  ;  and,  in  fact,  surrounding  the  latter  with  copper,  he  increased 
the  power  immensely.  (Fig.  283.) 

All  his  arrangements  were  so  peculiarly  neat  and  compact.  An  apparatus 
is  sold  at  Elliott’s  (Fig.  282  a),  called  Wollaston's  calorimeter,  consisting  of  one 
pair  of  4-in.  zinc  and  double  copper  plates,  movable  in  and  out  of  a  mahogany 


334 


ELECTRICITY. 


trough.  By  this  simple  arrangement  the  calorific  effect  of  an  electric  current 
is  shown  by  the  ignition  of  fine  platinum  wire,  stretched  between  the  ter¬ 
minals  of  the  two  metallic  elements,  zinc  and  copper. 

We  now  come  to  the  first  important  change  in  the  adjustment  of  the  elements 
and  the  choice  of  fluids,  which  originated  with  the  late  Professor  Daniell.  His 


A 


a,  Wollastoi.’s  calorimeter;  b,  Grove’s  constant  Wollaston  wire-gauze  calorimeter.  The  gauze  facili' 
tates  the  escape  of  hydrogen,  and  this  form  is  more  constant. 


discovery  in  1836  of  a  “  constant  battery marks  an  era  in  the  construction  of 
batteries,  and  is  a  fundamental  or  starting-point  for  various  improvements 
in  the  convenience  of  using  and  adapting  this  valuable  source  of  electrical  or 
current  force.  In  this  work,  the  writer  prefers  that  each  author  and  inventor 
quoted  here  should  speak  for  himself :  the  enthusiasm  of  an  inventor  supplies 
expressive  language,  which  may  be  paraphrased,  but  can  rarely  be  improved.* 


A 


Fig.  283. 

a,  the  single  cell,  Daniell’s ;  b,  a  Daniell’s  battery 


“  The  liquid  employed  in  the  voltaic  batteries,  when  it  has  been  desired  to 
excite  them  to  the  utmost,  has  generally  been  a  mixture  of  sulphuric  and  nitric 
acids  diluted  with  water,  in  which  case  much  local  action  takes  place  from  the 
zinc  plates,  which  contributes  nothing  to  the  force  which  circulates,  and  which 


*  Daniell  s  “  Introduction  to  Chemical  Philosophy. 


VOLTAIC  ELECTRICITY. 


335 


rapidly  destroys  them.  Their  power,  moreover,  speedily  declines  by  the  zinc 
which  forms  upon  the  copper  plates;  and  they  are  very  inconstant  in  their 
action.  These  defects  are  obviated  in  the  construction  of  the  constant  bat¬ 
tery,  the  contrivance  of  the  author,  which  consists  of  a  series  of  single  cir¬ 
cuits,  constructed  upon  the  principle  of  a  central  disposition  of  the  active 
metal  with  regard  to  the  conducting  surface,  as  formerly  explained.  A  cell  of 
this  battery  consists  of  a  cylinder  of  copper,  3!  in.  in  diameter,  which  expe¬ 
rience  has  proved  to  afford  the  most  advantageous  distance  between  the  gene¬ 
rating  and  conducting  surfaces,  but  which  may  vary  in  height  according  to  the 
power  which  it  is  wished  to  obtain.  A  membraneous  tube,  formed  of  the  gullet 
of  an  ox,  is  hung  in  the  centre  by  a  collar  and  circular  copper  plate,  resting 
on  the  rim  placed  near  the  top  of  the  cylinder;  and  in  this  is  suspended,  by  a 


Fig.  284. 


T> 


wooden  cross  bar,  a  cylindrical  rod  of  amalgamated  zinc,  half  an  inch  in  dia¬ 
meter.  The  cell  is  charged  with  a  mixture  of  8  parts  of  water  to  1  part  of 
oil  of  vitriol,  which  has  been  saturated  with  sulphate  of  copper,  and  portions 
of  the  solid  salt  are  placed  upon  the  upper  copper  plate,  which  is  perforated 
like  a  colander,  for  the  purpose  of  keeping  the  solution  always  in  a  state  of 
saturation.  The  internal  tube  is  filled  with  the  same  acid  mixture,  without  the 
copper.  A  tube  of  porous  earthenware  may  be  substituted  for  the  membrane, 
with  great  convenience,  but  probably  with  some  loss  of  power.  A  number  of 
such  cells  admit  of  being  connected  together  very  readily  into  a  compound 
circuit,  and  will  maintain  a  perfectly  equal  and  steady  current  for  many  hours 
together,  with  a  power  far  beyond  that  which  can  be  produced  by  any  other 
arrangement  of  a  similar  quantity  of  the  same  metals.  The  surface  of  the 
conducting  metal  is  thus  perpetually  renewed  by  the  deposition  of  pure  copper, 
and  the  counteraction  of  zinc  or  any  other  precipitated  metal  effectually  pre¬ 
vented.  The  minor  affinity  of  the  copper  for  the  acid,  however,  still  remains ; 
and  such  an  opposition  could  only  be  effectually  avoided  by  the  employment 


336 


ELECTRICITY. 


of  platinum  plates,  perpetually  renewed  by  the  decomposition  in  the  circuit 
of  chloride  of  platinum.  Such  an  arrangement  would  be  perfect,  but  too  costly 
for  ordinary  applications. 

“  One  of  the  cells  of  the  constant  battery  is  represented  (Fig.  284).  a  b  c  d  is  a 
copper  cylinder,  in  which  is  placed  a  smaller  cylinder  of  porous  earthenware. 
Upon  the  upper  part  of  the  copper  cylinder  rests  a  perforated  colander,  h  i, 
through  which  the  earthenware  cylinder  passes ;  l  m  is  a  cast  rod  of  amalga¬ 
mated  zinc,  resting  upon  the  top  of  the  interior  cylinder  by  a  cross-piece  of 
wood,  and  forming  the  axis  of  the  arrangement.  The  cell  is  charged  by 
pouring  into  the  earthenware  cylinder  water  acidulated  with  one-eighth  part 
of  its  bulk  of  oil  of  vitriol,  the  space  between  the  earthenware  tube  and  the 
copper  being  filled  with  the  same  acidulated  water,  saturated  with  sulphate  of 
copper,  and  solid  sulphate  being  placed  in  the  colander.  A  number  of  such 
cells  may  be  connected  into  a  compound  circuit  by  wires  attached  to  the  copper 
cylinders,  and  fastened  to  the  zinc  by  clamps  and  screws,  as  shown  below. 

“A  more  powerful  combination  upon  the  same  principle,  thou.  Th  not  so 
constant  in  its  working  or  conveniently  applicable  to  such  extensive  operations 
as  that  of  the  constant  battery,  has  been  contrived  by  Professor  Groves  (Fig. 
285),  who  makes  use  of  conducting  plates  of  platinum-foil,  immersed  in  strong 


Fig.  285. — A  Groves's  Battery. 


nitric  acid,  separated  from  the  dilute  sulphuric  acid,  in  which  the  zinc  is 
plunged,  by  a  diaphragm  of  porous  earthenware.  The  conducting  po  ver  of 
the  liquid  portion  of  the  combination  is  of  the  most  perfect  kind,  and  the 
hydrogen  which  travels  in  the  circuit  is  immediately  absorbed  by  the  ac.d  upon 
the  conducting  plate,  and,  reacting  upon  it,  decomposes  it  with  the  evomtion 
of  copious  fumes  of  nitrous  gas.  It  has  been  already  seen  that  a  single  cell  of 
this  construction  is  capable  of  overcoming  the  exterior  resistance  of  a  volta¬ 
meter  ;  and  a  very  efficient  series  may  thus  be  made  with  the  bowls  of  tobacco- 
pipes  and  corresponding  pieces  of  platinum-foil.” 

Mr.  Warren  De  la  Rue  and  Hugo  Muller  have  invented  another  entirely 
new  form  of  constant  battery,  which  the  authors  recommend  strongly  *  to  the 
chemist  and  physicist.  “  As  a  ready  source  of  dynamic  electricity  always  at 
hand,  and  that  especially  when  from  a  few  hundreds  to  several  thousand  ele¬ 
ments  are  requisite,  it  will  be  found  to  be  valuable,  handy,  and  compact.  In 


*  “  Journal  of  Chemical  Society,”  November,  i863, 


VOLTAIC  BA  TTERIES. 


337 


its  construction  no  porous  cell  is  needed,  and  the  electrolyte  is  solid  and  very 
nearly  insoluble,  so  that  practically  the  electro-positive  metal  is  scarcely  at¬ 
tacked,  even  when  the  elements  are  left  immersed  with  the  electrodes  discon¬ 
nected  for  several  weeks.  In  our  battery  the  generating  or  electro-positive 
metal  is  zinc,  which  it  is  better  to  amalgamate,  although  it  is  not  essential  to 
do  so ;  the  negative  metal  is  silver,  and  the  electrolyte  solid  chloride  of  silver, 
the  whole  being  immersed  in  a  solution  of  chloride  of  sodium  or  chloride  of 
zinc.  The  solution  we  generally  use  contains  25  grammes  of  common  salt  to 
a  like  quantity  of  distilled  water  (219  grains  to  a  pint).  It  is  not  desirable  to 
use  common  water  for  dissolving  the  chloride  of  sodium,  as  the  carbonates 
present  cause  a  cloudiness  by  precipitating  the  zinc  as  carbonate  when  the 
battery  is  in  action.  The  form  of  the  battery  which  we  have  adopted  is  repre¬ 
sented  in  Figs.  286  and  287;  but  where  a  very  large  number  of  elements  is 
wanted,  it  is  more  economical  and  convenient  to  employ  a  modification,  pre¬ 
sently  to  be  described.  The  zinc  element  is  formed  of  Belgian  zinc  wire 
(English  zinc  being  too  impure  to  be  used  advantageously),  2f  in.  (6  centi¬ 
metres)  long  and  o‘2  in.  (5T  mm.)  diameter.  The  electro-negative  element 
consists  of  a  wire  of  pure  silver  <ro3  in.  (077  mm.)  in  diameter,  and  round 
this  is  cast*  a  cylindei  of  chloride  of  silver,  o-22  in.  (5-6  mm.)  in  diameter. 


is. 


Fig.  286. 

The  silver  wire  projects  about  o'2  in.  (5  mm.)  beyond  the  bottom  end  of  the 
chloride  cf  silver,  and  about  l|  in.  (3’8  centimetres)  beyond  the  top  end  of  it, 
so  as  to  permit  of  its  connection  with  the  zinc  of  the  next  pair  of  elements 
The  cells  are  conveniently  formed  out  of  1  oz.  vials,  by  cutting  off  the  necks  by 
a  diamond  or  an  ignited  splint-coal. 

“  The  zinc  and  chloride  of  silver  rods  pass  through,  and  are  supported  by,  a 
lath  or  bar  of  varnished  mahogany,  A  A,  which  is  pierced  for  that  purpose 
The  ends  of  this  bar  are  also  pierced  with  two  larger  holes,  through  which 
two  supporting  glass  rods,  B  B,  pass  ;  it  slides  up  and  down  these  rods  freely, 
and  is  retained  in  any  required  position  by  means  of  the  vulcanized  caoutchouc 


*  "In  making  these  cylinders  a  mould  which  was  designed  for  casting  rods  of  lunar  caustic  (nitrate  of 
silver)  W3s  found  to  he  convenient.  The  mould  contained  a  series  of  recesses  which  permuted  of  several 
tods  be'ng  cast  at  a  time.  The  silver  wire  was  held  firmly  in  the  centre  of  the  cylindrical  ’ecess  by 
passing  through  a  hole  in  the  bottom  ot  the  mould,  and  by  a  series  of  arms  projecting  over  the  mouth 
ot  each  recess  at  a  sufficient  distance  to  permit  of  the  lused  chloride  Ivemg  poured  into  them.” 

22 


338 


ELECTRICITY. 


collars,  C  C,  on  which  it  rests  ;  these  grip  the  rods,  B  B,  with  adequate  firmness 
to  support  the  bar,  but  at  the  same  time  permit  of  its  being  moved  up  and 
down  with  sufficient  freedom  to  immerse  the  element  partially  or  wholly,  as  in 
Fig.  286,  or  to  raise  them  entirely  out  of  the  liquid,  as  in  Fig.  287.  The  raising 
is  conveniently  performed  by  placing  the  two  forefingers  of  each  hand  under 
the  collars,  C  C,  and  pressing  the  thumbs  on  the  top  of  the  glass  rods,  B  B. 
The  lowering  of  the  bar  can  be  effected  by  pressing  down  the  two  ends.  These 
glass  rods  should  not  be  varnished  on  that  portion  over  which  the  vulcanized 
collars  have  to  slide,  as  the  varnish  causes  too  much  friction  and  a  liability 
of  jerking ;  below  this  point  they  may  be  varnished  with  advantage.  They 

j 


B  n 


are  cemented  into  the  base  of  varnished  mahogany,  D  D,  in  which  is  made  a 
series  of  recesses  to  fit  the  cells,  E,  and  keep  them  in  their  places.  This  base 
rests  on  feet  of  vulcanite  to  increase  the  insulation.  The  rods  of  zinc  and 
chloride  of  silver  are  prevented  from  falling  through  the  holes  in  bar  A  A  by 
means  of  heads  formed  in  the  zinc  by  hammering  the  wire  while  it  is  held  in 
a  properly  shaped  tool,  and  on  the  chloride  of  silver  by  suitably  shaping  the 
upper  end  of  the  mould  into  which  it  is  cast.  A  collar  of  caoutchouc  is  placed 
on  the  lower  end  of  the  zinc  element  to  prevent  contact  between  it  and  the 
rod  of  chloride  of  silver.  Another  plan  of  support  is,  however,  more  advan¬ 
tageous  when  a  very  numerous  series  of  elements  is  used,  as  shown  in  Fig. 
288,  for  it  permits  both  of  economizing  the  chloride  of  silver  and  of  readily 
renewing  it  from  time  to  time.  Pieces  of  gutta  percha  or  ebonite,  I  I,  are 
well  fitted  into  the  bar  A ;  they  are  pierced  with  a  hole  just  large  enough  to 
permit  of  the  silver  wire,  M,  being  drawn  through  them.  The  zincs  are  held 
in  position  by  means  of  the  vulcanized  collars,  N,  while  a  second  collar,  O, 
serves  as  a  clip  for  making  connection  with  the  silver  wire,  M,  which  is  done 
by  passing  the  wire  between  the  zinc  and  the  collar,  o. 

“  It  should  be  observed  that,  as  the  chloride  of  silver  becomes  reduced,  the 
resulting  spongy  silver  is  of  greater  diameter  and  less  regular  in  form  than  the 
original  rods  of  chloride.  It  is  evident,  therefore,  that  the  reduced  silver  can¬ 
not  be  withdrawn  through  the  holes  in  the  bar  A  A  with  the  arrangement  shown 
in  Figs.  286  and  287 ;  moreover,  that  portion  of  the  chloride  which  remains 
out  of  the  liquid  in  the  arrangement  (Figs.  286  and  287)  is  not  reduced;  and 
although  no  silver  is  ultimately  lost,  yet  a  portion  of  the  useful  effect  of  its 
chloride  is  sacrificed;  and,  consequently,  the  arrangement  of  Fig.  288  is  both 


VOLTAIC  BATTERIES. 


339 


more  economical  and  convenient.  When  the  chlorine  is  more  or  less  com¬ 
pletely  exhausted  by  the  reduction  of  the  cylinders  through  their  entire  thick¬ 
ness,  the  resulting  rods  of  spongy  silver  should  be  placed  in  a  vessel  of  water 
acidulated  with  hydrochloric  acid  and  some  rods  of  zinc,  in  order  to  reduce 


FIG.  288. 


any  undecbmposed  chloride,  especially  at  their  upper  ends.  After  removal  of 
the  zinc,  the  spongy  silver  must  be  treated  with  dilute  hydrochloric  acid,  and 
well  washed  to  remove  all  traces  of  zinc.  Very  little,  if  any,  loss  of  silver 
occurs,  and  the  cost  of  renewal  of  the  electrolyte  is  chiefly  one  of  labour. 

“  There  are  many  other  forms  of  batteries.  Professor  Hare,  of  Philadelphia, 
devised  an  enormous  calorimeter.  Mr.  Alfred  Smee’s  battery,  A,  I'ig.  289,  is 
a  most  useful  and  popular  form  ;  it  consists  of  a  plate  of  silver,  covered  with 
black  powder  of  platinum,  and  surrounded  with  amalgamated  zinc.  It  is  in 
form  a  reversed  Wollaston  battery.  The  conductor,  the  platinized  silver,  is 
placed  inside,  and  the  amalgamated  zinc  outside.” 

Sturgeon’s  battery,  u,  Fig.  289,  is  a  cylindrical  modification  of  Wollaston’s 
battery.  It  consists  of  two  copper  cylinders  brazed  on  to  a  foot,  so  as  to  form 
a  hollow  cylindrical  vessel.  Into  this  is  placed  a  cylinder  of  zinc,  which  is 
made  movable,  so  that  the  surface  can  be  scraped  and  cleaned,  or  the  whole 
cylinder  renewed. 

If  amalgamated  zinc  is  used,  the  mercury  must  be  used  sparingly,  or  else 
the  excess  will  fall  to  the  bottom  of  the  copper  cylindrical  vessel,  and,  amal¬ 
gamating  the  copper,  will  soon  pass  through  the  metal,  rendering  it  so 
brittle  that  any  hard  substance,  even  the  finger.,  may  be  thrust  through  it ; 
indeed,  very  pure  zinc  cylinders  should  be  used  in  preference  to  amalgamated 
zinc  in  this  particular  instance. 


2 ' — 2 


340 


ELECTRICITY. 


a,  Smee’s  single  cell;  B,  Sturgeon’s  cylindrical  battery  ,  c,  Mullins’s  sustaining  battery,  d,  Sturgeon’s  cast 

iron  and  ama'gamated  zinc  battery. 


C,  Fig.  289,  is  a  single  cell  of  Mullins’s  sustaining  battery.  It  consists  of 
a  narrow  cylindrical  slip  of  sheet  zinc,  surrounding  a  copper  vessel  closed  at 
the  bottom  with  wood,  and  a  shelf  provided  at  the  top  to  carry  crystals  of  the 
blue  sulphate  of  copper.  The  copper  vessel  is  enveloped  with  a  membrane, 
and  the  whole  arrangement  placed  in  a  stoneware  jar.  Sulphate  of  copper  is 
used  inside  the  membrane,  and  chloride  of  ammonium  or  dilute  sulphuric 
acid  outside  the  membrane.  The  title  of  sustaining  battery  is  well  maintained. 
The  writer  has  seen  them  in  use,  and  rough  use  too,  and  found  that  they  gave 
a  distinct  current  for  months;  always,  of  course,  taking  care  that  water  is 
added,  so  that  the  salts  do  not  dry  up. 

D,  Fig.  289,  Sturgeon’s  battery  of  cast  iron  and  amalgamated  rolled  zinc. 
It  consists  of  two  cylinders,  one  of  cast  iron  and  the  other  of  amalgamated 
zinc ;  they  are  placed  one  within  the  other,  in  dilute  sulphuric  acid,  contained 
in  a  stoneware  jar.  This  arrangement  is  well  adapted  for  quantity  e'ffects  ;  but 
its  intensity  is,  of  course,  very  low.  This  form  is  remarkably  economical,  and 
when  made  on  the  large  scale  is  powerful. 

All  these  batteries  can  be  obtained  from  Messrs.  Elliot,  of  Charing  Cross, 
and  the  youthful  student  in  looking  at  so  many  forms  is  apt  to  be  puzzled  with 
regard  to  selection,  and  naturally  asks,  Which  is  the  best  ?  The  answer  should 
be.  What  do  you  want  to  use  the  battery  for ?  If  you  wish  to  make  electro¬ 
types,  and  to  throw  down  silver  or  gold  upon  other  surfaces  by  the  voltaic 
current,  you  cannot  select  a  cheaper,  more  convenient,  and  constant  battery 
than  that  of  Smee  or,  better  still,  Daniell.  If  the  battery  is  required  for  the 
more  brilliant  effects,  such  as  heating  platinum  wire,  deflagrating  the  metals, 
and  producing  the  electric  light,  there  is  no  battery  yet  constructed  which 
surpasses  Professor  Groves’s  for  certainty  and  steadiness  of  results. 

If  you  require  a  battery  to  work  a  small  telegraphic  system,  or  to  move 
electro-magnetic  machines,  use  a  few  cells  of  Smee,  arranged  on  a  bar  of 
wood,  and  dropping  into  a  trough  made  of  stoneware  and  divided  into  cells, 
all  of  which  contain  dilute  sulphuric  acid  (by  making  a  stand  and  two  up¬ 
rights  with  pulleys,  the  metals  can  be  drawn  out  by  catgut  cords  and  counter¬ 
poise  weights  at  the  sides  when  not  in  use,  and  immediately  placed  in  position 
when  required  to  perform  the  above-named  work) ;  or,  still  better,  the  im¬ 
proved  bichromate  battery,  which  is  one  of  the  best  forms  that  can  be  em- 


VOLTAIC  ELECTRICITY. 


34i 


Fig.  290. 


ployed :  its  advantages  are  freedom  from  smell,  economy,  and  it  is  always 
ready  for  immediate  use.  Apps’s  patent  battery  is  the  best  of  all  forms  where 
the  bichromate  solution  is  used :  the  proportions  are  a  saturated  solution  of 
bichromate  of  potash  in  water,  with  one-seventh  part  of  sulphuric  acid.  A 
two-cell  battery  on  this  principle  is  shown  in  Fig.  290,  and  consists  of  two 
plates  of  zinc,  surrounded  by  three  plates  of  carbon,  so  arranged  that  the  plates 
can  be  placed  in,  or  out  of,  the  bichromate  solution. 

Dynamical  Electrical  Phenomena  obtained  from  the 

Voltaic  Battery. 

* 

The  effects  obtainable  from  the  current  of  electricity  flowing  or  in  motion 
from  pole  to  pole,  and  through  the  whole  system  of  a  voltaic  battery,  can  be 
summed  up  under  four  heads: 

1.  Chemical  phenomena — chemical  action. 

2.  Calorific  and  lighting  effects — heat  and  light. 

3.  Magnetic  phenomena — magnetism. 

4.  Dynamical  effects— mechanical  motion. 

As  the  action  of  a  voltaic  battery  depends  on  “chemical  action,”  it  will  be 
most  interesting  to  commence  the  inquiry  by  speaking  first  of  the  chemical 
phenomena  which  may  be  rendered  evident  during  the  passage  ot  a  current 
of  electricity  through  any  given  substance,  the  conditions  ot  success  being 


342 


ELECTRICITY. 


first  understood  to  be  the  fluidity  of  the  matter  under  decomposition  and  its 
power  of  conducting  the  electric  current. 

“The  first  experiments,”  says  a  clear-headed  writer  in  1819,  “made  upon 
the  pile  in  this  country  appear  to  have  been  made  by  Messrs.  Nicholson  and 
Carlisle.  After  observing  the  effects  then  already  ascribed  to  the  piles,  on 
bringing  the  wires  from  each  end  of  the  column  in  contact  with  a  drop  of 
water,  they  observed  a  disengagement  of  bubbles  of  some  elastic  fluid;  on 
close  examination,  they  took  the  gas  to  be  hydrogen.  They  then  took  a  glass 
tube,  about  half  an  inch  in  diameter,  into  each  end  of  which  a  cork  was  in¬ 
serted,  the  tube  being  filled  with  water.  Through  each  cork  was  introduced 
a  brass  wire,  so  that  the  ends  of  the  wires  in  the  glass  were  about  if  of  an 
inch. 

“  The  pile  employed  consisted  of  thirty-six  half-crowns,  and  as  many  pieces 
of  zinc  and  wet  pasteboard.  The  zinc  end  of  the  pile  was  then  connected 
with  one  of  the  wires  in  the  tube,  and  the  silver  end  to  the  other,  so  that  the 
circuit  formed  by  the  wires  was  separated  by  the  water  in  the  tube  placed  be¬ 
tween  them.  A  stream  of  bubbles  was  observed  at  the  end  of  the  wire,  in  the 
tube  connected  with  the  silver  end  of  the  pile.  No  gas  was  disengaged  from 
the  opposite  wire,  but  it  speedily  became  tarnished,  first  of  an  orange  colour  and 
ultimately  black.  The  tube  was  reversed,  when  it  was  observed  that  the  wire 
which  in  the  first  experiment  became  black  gave  out  bubbles,  while  that  which 
previously  gave  out  bubbles,  in  its  turn,  became  tarnished.  The  emission  of 
gas  from  the  wire  connected  with  the  silver  end  of  the  pile  was  constant  and 
uniform,  except  when  a  metallic  current  was  formed  between  the  ends  of  the 
pile,  during  which  no  gas  whatever  appeared.  It  was  observed  that  when  this 
metallic  conductor  was  removed  the  appearance  of  the  gas  was  not  immediate, 
since  there  was  an  interval  of  two  seconds  between  removing  the  wire  and  the 
appearance  of  the  bubbles.  After  the  process  had  continued  two  and  a  half 
hours,  a  bulk  of  gas  was  produced  equal  to  two-thirds  of  a  cubic  inch.  This 
gas  was  mixed  with  an  equal  bulk  of  common  air,  and  exploded  on  the  appli¬ 
cation  of  a  lighted  taper. 

“These  ingenious  experimenters,  supposing  the  phenomena  tG  arise  from 
the  decomposition  of  the  water,  thought  it  surprising  that  the  hydrogen  should 
make  its  appearance  at  a  distance  of  if  in.  from  the  point  where  the  oxygen 
was  disposed  of.  They  made  the  experiment  with  a  longer  tube,  but  no  appear¬ 
ance  of  gas  was  observed  at  the  distance  of  36  in.  When  they  introduced  an 
infusion  of  litmus,  instead  of  pure  water,  they  observed  that  the  fluid  in  the 
vicinity  of  the  wire  connected  with  the  zinc  end  of  the  pile  became  red, 
and  hence  were  led  to  suppose  that  an  acid  was  produced.  The  fluid  at  the 
other  wire  was  not  changed;  but  gas,  as  usual,  was  evolved.  Mr.  Nicholson 
ascertained  that  the  zinc  end  of  the  pile  was  in  the  plus  state  of  electricity, 
and  the  opposite  end  was  in  the  minus  state. 

“  They  next  varied  the  experiment  by  inserting  in  the  tube  of  water  wires 
of  platina,  instead  of  brass.  Under  these  circumstances  both  the  wires  gave 
out  gas,  'out  neither  of  them  was  tarnished.  There  appeared  to  be  a  larger 
volume  of  gas  from  the  silver  end  than  from  the  zinc.  The  apparatus  was  so 
arranged  that  the  gases  were  separately  collected.  On  examination,  the  gas 
from  the  silver  end  was  found  to  be  hydrogen,  as  before,  and  that  from  the 
zinc  end  oxygen.  Their  proportions  were  found  to  agree  with  the  component 
parts  of  water. 

“  The  galvanic  energy  evinced  in  the  decomposition  of  bodies  was  further 


VOLTAIC  ELECTRICITY. 


343 


prosecuted  by  Mr.  Cruikshank,  of  Woolwich;  he  employed  in  his  experiments 
a  pile  consisting  of  from  40  to  100  pairs  of  plates  of  silver  and  zinc,  about 
in.  square.  He  also  provided  a  glass  tube,  into  each  end  of  which  was  inserted 
a  cork,  one  of  whicn  was  closely  cemented,  so  as  to  be  air-tight.  Through 
each  of  the  corks  a  silver  wire  was  passed,  the  ends  in  the  tube  being  a  certain 
distance  from  each  other.  The  tube,  being  filled  with  water,  was  placed  per¬ 
pendicularly  in  a  cup  containing  water,  with  the  uncemented  cork  downwards. 
On  the  em  s  of  the  wires  being  connected  with  the  ends  of  the  pile,  bubbles 
began  to  appear  at  the  wire  connected  with  the  silver  end  of  the  pile;  at  the 
end  of  the  other  wire  bubbles  also  appeared,  and  at  the  same  time  a  white 
cloud,  which  became  of  a  darker  colour,  and  ultimately  purple  and  black. 
The  gas  was  collected,  and  found  to  consist  of  oxygen  and  hydrogen  in  the 
proportion  of  one  to  three.  The  wire  from  the  zin._  end  of  the  pile  was  much 
corroded  and  even  dissolved,  which  accounted  for  the  deficiency  of  oxygen  in 
the  gaseous  form.  Mr.  Cruikshank  very  truly  conjectured  that  tfk  cloud  that 
became  black  was  muriate  of  silver,  the  muriatic  acid  having  been  derived 
from  some  muriatic  salt  in  the  water  employed. 

“With  a  view  to  ascertain  how  far  his  conjecture  was  right,  he  filled  the 
tube  with  distilled  water,  containing  a-n  infusion  of  litmus.  The  appearance 
with  regard  to  the  evolution  of  gas  was  similar  to  the  last  experiment ;  but  the 
fluid  in  the  vicinity  of  the  wire  coming  from  the  zinc  end  of  ti  e  pile  became 
of  a  red  colour,  while  the  fluid  about  the  other  gradually  lost  its  purple  tinge 
and  became  of  a  deeper  blue.  In  short,  an  acid  appeared  to  be  produced 
about  the  fornur  wire,  and  an  alkali  about  the  latte*.  An  infusion  of  Brazil 
wood  underwent  similar  changes  to  those  observed  by  an  acid  and  an  alkali. 

“  In  all  these  experiments  a  quantity  of  silver  was  oxidated,  and  where  water 
was  employed  a  portion  was  always  dissolved,  some  of  which  was  precipitated 
at  the  wire  from  the  silver  end  of  the  pile  by  the  alkali  which  was  produced. 
This  ingenious  experimenter,  knowing  that  hydiogen  in  its  nascent  state 
was  capable  of  reducing  most  metallic  oxides,  filled  the  tube  with  a  solu¬ 
tion  of  acetate  of  lead,  and  found  that  the  hydrogen  all  disappeared,  being 
employed  in  the  reduction  of  the  metal ;  by  this  means  he  also  obtained  pure 
oxygen  gas.  The  same  was  observed  when  sulphate  of  copper  and  nitrate  of 
silver  were  employed.  When  a  solution  of  muriate  of  ammonia  was  employed 
in  the  tube,  the  silver  became  oxidated,  the  oxide  combined  with  the  muriatic 
acid  of  the  salt,  and  the  liquor  afterwards  smelt  strongly  of  ammonia.  In  a 
similar  way  the  muriate  of  soda  and  nitrate  of  magnesia  were  decomposed. 
Mr.  Cruikshank  repeated  the  above  experiments ;  but,  instead  of  silver  wires,  he 
inserted  into  the  tubes  gold  wires.  The  proportion  of  oxygen  gas  was  now 
much  greater  than  with  the  silver  wires,  the  gold  not  being  susceptible  of  oxi¬ 
dation  in  the  process. 

“His  next  attempt  was  to  collect  the  gas  separately;  this  he  effected  by 
a  tube  about  10  in.  long,  which  was  bent  into  the  form  of  the  letter  V;  the 
wires  were  passed  through  corks  firmly  cemented  into  the  ends  of  the  tubes, 
coming  near  to  the  angular  point.  A  small  hole  was  made  in  the  angular  point 
of  the  tube,  by  which  it  was  filled  with  water.  The  tube  was  then  inverted 
in  a  cup  of  water,  and  the  connection  made  with  the  other  ends  of  the  wires 
and  the  pile.  By  this  contrivance  the  hydrogen  gas  ascended  into  one  leg  of 
the  tube,  and  the  oxygen  into  the  other,  lie  next  filled  the  tube  next  employed, 
instead  of  water,  with  muriate  of  lime :  the  rapidity  of  the  process  was  much 
increased  ;  the  gold  wire  on  the  zinc  side  became  partly  dissolved,  and  the  fluid 


344 


ELECTRICITY. 


in  its  vicinity  assumed  a  yellow  colour.  When  the  tube  was  opened,  a  strong 
smell  of  aqua  regia  was  perceived.  Similar  phenomena  were  observed  when 
muriate  of  soda  was  employed.  Many  very  anomalous  facts  were  known  in 
chemistry  long  previous  to  the  discovery  of  galvanism.  All  those  chemical 
phenomena  under  which  the  appearance  called  arborescence  was  observed 
were  inexplicable  till  it  was  shown  by  seme  experiments,  published  in  ‘Nichol¬ 
son’s  Journal’  (vol.  xv.,  p.  94),  that  galvanism  is  the  cause  of  these  singular 
phenomena.  In  the  experiment  where  lead  is  so  beautifully  precipitated  by 
suspending  a  piece  of  zinc  in  a  solution  of  acetate  of  lead,  the  zinc  first  receives 
a  small  portion  of  lead,  which  with  the  lead  forms  a  galvanic  combination. 
The  lead,  if  no  solution  of  lead  were  present,  would  now  give  out  hydrogen 
gas ;  but  the  hydrogen,  instead  of  appearing  in  that  form,  combines  with  the 
oxygen  of  the  oxide,  and  the  metallic  lead  is  formed  at  the  same  point.  Hence 
the  lead  appears  to  grow  from  the  last  point  formed,  which  gives  the  appear¬ 
ance  of  vegetation.  That  this  effect  does  not  depend  upon  the  presence  of 
zinc  may  be  proved  by  the  following  experiment : 

“  Tie  on  one  end  of  a  glass  tube,  about  half  an  inch  wide,  a  piece  of  bladder, 
so  that  it  may  hold  water,  and  fill  it  with  a  solution  of  acetate  of  lead ;  inth 
the  other  end  insert  a  cork  loosely,  and  through  the  cork  let  a  platina  wire 
pass  within  about  half  an  inch  of  the  bladder.  Into  a  wine-glass  put  some 
diluted  muriatic  acid,  in  which  place  a  zinc  wire.  When  the  tube  with  the 
bladder  is  immersed  in  the  wine-glass,  if  that  part  of  the  zinc  wire  that  is 
without  the  glass  be  brought  in  contact  with  that  part  of  the  platina  wire  with¬ 
out  the  tube,  beautiful  crystals  of  metallic  lead  will  appear  upon  the  platina 
wire.  If  the  acetate  of  lead  be  removed,  and  a  dilute  acid  put  in  its  place, 
bubbles  of  hydrogen  will  appear  on  the  platina  wire. 

“  Another  experiment,  similar  to  that  of  the  lead  tree,  and  equally  anomalous, 
has  been  long  known  in  chemistry.  If  a  plate  of  glass  be  smeared  over  with 
a  solution  of  nitrate  of  silver,  and  a  brass  pin  or  a  piece  of  zinc  wire  be  laid 
in  the  middle  of  the  plate,  beautiful  ramifications  of  silver  will  soon  appear 
as  if  growing  out  of  the  pin.  very  much  resembling  vegetation.  By  observing 
the  process  by  a  magnifying-glass,  each  branch  of  this  arborescence  may  be 
seen  to  grow  from  the  side  or  end  of  another,  which  proves  that  the  silver 
forming  the  vegetative  appearance  is  not  reduced  by  the  oxidable  metal  laid 
on  the  plate,  but  by  something  at  the  successive  points  of  the  silver  branches. 
With  a  view  to  ascertain  this  fact,  one  half  of  the  plate  of  glass  should  be 
smeared  with  nitrate  of  silver  and  the  other  half  with  dilute  muriatic  acid. 
If  a  piece  of  zinc  wire  be  tied  to  a  piece  of  platina  wire,  and  the  compound 
wire  be  so  bent  that  the  zinc  may  touch  the  dilute  acid  and  the  platina  the 
nitrate  of  silver,  the  ramifications  of  silver  will  soon  appear  on  the  platina 
wire.  That  the  silver  is  reduced  by  the  hydrogen  carried  in  the  galvanic 
current  is  probable  from  varying  the  experiment  as  follows: 

“  If,  instead  of  smearing  the  plate  with  nitrate  oi  silver,  the  whole  be 
covered  with  dilute  acid,  and  the  same  compound  arc  be  laid  upon  it,  the  platina 
will  give  out  bubbles  of  hydrogen.  In  the  common  way  of  making  this  expe¬ 
riment  with  the  pin,  as  well  as  the  variation  above  stated,  it  appears  that  the 
process  is  kept  up  by  the  galvanic  current  which  furnishes  the  hydrogen.  The 
pin  first  reduces  a  small  portion  of  silver,  which  forms  a  galvanic  combination 
with  the  pin.  The  hydrogen,  which,  bat  for  the  presence  of  the  remaining 
nitrate  of  silver,  would  appear  in  the  gaseous  form,  is  employed  to  deprive  the 
silver  of  its  oxygen.  With  the  compound  arc  the  zinc  does  not  require  to 


FAR  ABA  Y'S  RESEARCHES. 


345 


touch  the  nitrate  of  silver,  because  the  platina  with  the  zinc  is  already  a  gal¬ 
vanic  combination.  The  theory  of  whitening  common  pins  can  be  explained 
only  on  this  principle.  The  tin  in  a  small  pioportion  is  dissolved  in  the  tar¬ 
trate  of  potash ;  pieces  of  metallic  tin  with  the  pins  are  also  present.  *The 
two  latter  form  the  galvanic  combination,  and  a  portion  of  tin  is  reduced  from 
the  solution  upon  the  pins,  to  which  they  owe  their  whiteness.  We  may  gene¬ 
rally  conclude  that,  in  all  cases  where  one  metal  becomes  the  precipitant  of 
another,  the  precipitation  is  much  facilitated  by  the  agency  of  the  galvanic 
combination  formed  between  the  precipitating  and  the  precipitated  metals, 
and  the  consequent  presence  of  hydrogen. 

“  If  a  piece  of  zinc  be  introduced  into  a  solution  of  sulphate  of  copper,  the 
zinc  in  the  first  instance  becomes  covered  with  copper,  and  the  effect  appears 
to  stop.  If,  however,  a  very  small  excess  of  sulphuric  acid  be  added,  the 
process  will  go  on  with  such  rapidity  that  the  copper  becomes  precipitated  in  a 
very  short  time.  By  minutely  observing  the  process,  the  copper  will  be  seen  to 
be  reduced  upon  that  already  produced,  which  is  a  proof  that  it  is  not  done  by 
the  mere  agency  of  zinc.  It  appears  very  evident  that,  when  a  galvanic  com¬ 
bination  of  zinc  with  any  lesser  oxidable  metal  is  placed  in  a  dilute  acid, 
a  much  larger  quantity  of  hydrogen  will  be  evolved  from  the  lesser  oxidable 
wire  than  could  possibly  be  produced  by  any  electrical  intensity  generated  by 
the  contact  of  the  bodies  employed  ;  but  that,  independently  of  this,  there  is  an 
immense  quantity  of  electricity  generated  during  the  chemical  action,  by 
which  the  hydrogen  is  transported  from  the  greater  oxidable  surface  to  the 
lesser  one.  If  the  quantity  of  hydrogen  produced  depended  upon  the  attrac¬ 
tions  of  the  wires  for  the  elements  of  the  water,  this  power  would  depend  upon 
the  electrical  intensity  alone,  and,  of  course,  upon  the  series  of  the  galvanic 
battery,  whatever  might  be  its  surface;  but  it  is  found  that  the  power  of 
galvanism  to  decompose  water  is  much  increased  by  an  increase  of  surface 
only.” 

Any  clever  experimentalist,  reading  this  account  carefully,  would  at  once 
perceive  that  these  experiments  were  capable  of  great  extension,  and,  thus 
stimulated,  his  mind  might  pass,  like  that  of  Daniell  and,  later,  of  Warren  De 
la  Rue,  to  indicate  the  discovery  of  the  electrotype,  which  Jacobi  in  Russia 
and  Spenser  in  England  brought  before  the  scientific  world,  under  the  names 
of  “  Galvano-plastic  ”  and  “  Electrography.” 

But  it  was  left  for  the  genius  of  Faraday  to  put  “electro-chemical  decom¬ 
position  ”  in  a  clear  light,  and,  in  fact,  to  devise  new  instruments  and  a  new 
nomenclature,  which  are  set  forth  in  the  seventh  series  of  his  “  Experimental 
Researches  in  Electricity:” — “On  Electro-chemical  Decomposition;  “On 
a  new  Measurer  of  Voltaic-electricity ;”  “On  the  Absolute  Quantity  of  Elec¬ 
tricity  associated  with  the  Particles  or  Atoms  of  Matter.” 

The  simplicity  of  Faraday’s  diction,  and  the  clearness  with  which  lie  c  e- 
scribes  the  phenomena  observed,  are  most  remarkable,  and  supply  a  “standard 
of  excellence  ”  which  scientific  writers  may  well  try  to  imitate.  1  he  following 
are  some  of 

“FARADAY’S  RESEARCHES.” 

The  theory  which  I  believe  to  be  a  true  expression  of  the  facts  of  electro¬ 
chemical  decomposition,  and  which  I  have  therefore  detailed  in  a  former 
series  of  these  Researches,  is  so  much  at  variance  with  those  previously 
advanced,  that  I  find  the  greatest  difficulty  in  stating  results,  as  I  think, 


ELECTRICITY. 


346 


correctly,  whilst  limited  to  the  use  of  terms  which  are  current  with  a  certain 
accepted  meaning.  Of  this  kind  is  the  term  pole,  with  its  prefixes  of  positive 
and  negative,  and  the  attached  ideas  of  attraction  and  repulsion.  The  general 
phraseology  is,  that  the  positive  pole  attracts  oxygen,  acids,  &c.,  or,  more 
cautiously,  that  it  determines  their  evolution  upon  the  surface  ;  and  that  the 
negative  pole  acts  in  an  equal  manner  upon  hydrogen,  conbustibles,  metals, 
and  bases.  According  to  my  view,  the  determining  force  is  not  at  the  poles, 
but  within  the  decomposing  body  ;  and  the  oxygen  and  acids  are  rendered 
at  the  negative  extremity  of  that  body,  whilst  hydrogen,  metals,  &c.,  are 
evolved  at  the  positive  extremity. 

To  avoid,  therefore,  confusion  and  circumlocution,  and  for  the  sake  of 
greater  precision  of  expression  than  I  can  otherwise  obtain,  I  have  delibe¬ 
rately  considered  the  subject  with  two  friends,  and,  with  their  assistance  and 
concurrence  in  framing  them,  I  purpose  henceforward  using  certain  other 
terms,  which  I  will  now  define.  The  poles,  as  they  are  usually  called,  are 
only  the  doors  or  ways  by  which  the  electric  current  passes  into  and  out  of 
the  decomposing  body  ;  and  they,  of  course,  when  in  contact  with  that  body, 
are  the  limits  of  its  extent  in  the  direction  of  the  current.  The  term  has  been 
generally  applied  to  the  metal  surfaces  in  contact  with  the  decomposing 
substance;  but  whether  philosophers  generally  would  also  apply  it  to  the 
surfaces  of  air  and  water,  against  which  I  have  effected  electro-chemical 
decomposition,  is  subject  to  doubt.  In  place  of  the  term  pole,  I  propose 
using  electrode *,  and  I  mean  thereby  that  substance,  or  rather  surface, 
whether  of  air,  water,  metal,  or  any  other  body,  which  bounds  the  extent  of 
the  decomposing  matter  in  the  direction  of  the  electric  current. 

The  surfaces  at  which,  according  to  common  phraseology,  the  electric 
current  enters  and  leaves  a  decomposing  body,  are  most  important  places  of 
action,  and  require  to  be  distinguished  apart  from  the  poles,  with  which  they 
are  mostly,  and  the  electrodes,  with  which  they  are  always,  in  contact.  Wish¬ 
ing  for  a  natural  standard  of  electric  direction  to  which  I  might  refer  these, 
expressive  of  their  difference  and  at  the  same  time  free  from  all  theory,  I  have 
thought  it  might  be  found  in  the  earth.  If  the  magnetism  of  the  earth  be  due 
to  electric  currents  passing  round  it,  the  latter  must  be  in  a  constant  direction, 
which,  according  to  present  usage  of  speech,  would  be  from  east  to  west,  or, 
which  will  strengthen  this  help  to  the  memory,  that  in  which  the  sun  appears 
to  move.  If  in  any  case  of  electro-decomposition  we  consider  the  decompo¬ 
sing  body  as  placed  so  that  the  current  passing  through  it  shall  be  in  the  same 
direction,  and  parallel  to  that  supposed  to  exist  in  the  earth,  then  the  surfaces 
at  which  the  electricity  is  passing  into  and  out  of  the  substance  would  have 
an  invariable  reference,  and  exhibit  constantly  the  same  relations  of  powers. 
Upon  this  notion  we  purpose  calling  that  towards  the  east  the  anode +,  and 
that  towards  the  west  the  cathodeX ;  and  whatever  changes  may  take  place  in 
our  views  of  the  nature  of  electricity  and  electrical  action,  as  they  must  affect 
the  natural  standard  referred  to  in  the  same  direction,  and  to  an  equal  amount 
with  any  decomposing  substances  to  which  these  terms  may  at  any  time  be 
applied,  there  seems  no  reason  to  expect  that  they  will  lead  to  confusion,  or 
tend  in  any  way  to  support  false  views.  The  anode  is  therefore  that  surface 


*  r)\rKTpov  and  oSos  a  nay 

t  an  up-wards,  060s  a  ivay ;  the  way  which  the  snn  rises 
t  Kara  da-wn-wards,  oSos  a  -way ;  the  way  which  the  sun  sets. 


FARADAY'S  RESEARCHES. 


347 


at  which  the  electric  current,  according  to  our  present  expression,  enters ;  it 
is  the  negative  extremity  of  the  decomposing  body;  is  where  oxygen,  chlorine, 
acids,  &c.,  are  evolved,  and  is  against  or  opposite  the  positive  electrode. 
The  cathode  is  that  surface  at  which  the  current  leaves  the  decomposing  body, 
and  is  its  positive  extremity  ;  the  combustible  bodies,  metals,  alkalies,  and 
bases,  are  evolved  there,  and  it  is  in  contact  with  the  negative  electrode. 

I  shall  have  occasion  in  these  Researches,  also,  to  class  bodies  together 
according  to  certain  relations  derived  from  their  electrical  actions  ;  and  wish¬ 
ing  to  express  those  relations  without  at  the  same  time  involving  the  expres¬ 
sion  of  any  hypothetical  views,  I  intend  using  the  following  names  and  terms: 
--Many  bodies  aie  decomposed  directly  by  the  electric  current,  their  elements 
being  set  free;  these  I  propose  to  call  electrolytes *.  Water,  therefore,  is  an 
electrolyte.  The  bodies  which,  like  nitric  or  sulphuric  acids,  are  decomposed 
in  a  secondary  manner  are  not  included  under  this  term.  Then  for  electro- 
chemically  decomposed  I  shall  often  use  the  term  electrolyzed,  derived  in  the 
same  way,  and  implying  that  the  body  spoken  of  is  separated  into  its  com¬ 
ponents  under  the  influence  of  electricity;  it  is  analogous  in  its  sense  and 
sound  to  analyze ,  which  is  derived  in  a  similar  manner.  The  term  electroly- 
tical  will  be  understood  at  once.  Muriatic  acid  is  electrolytical ;  boracic  acid 
is  not. 

Finally,  I  require  a  term  to  express  those  bodies  which  can  pass  to  the  elec¬ 
trodes ,  or,  as  they  are  usually  called,  the  poles.  Substances  are  frequently 
spoken  of  as  being  electro-negative  or  electro-positive ,  according  as  they  go 
under  the  supposed  influence  of  a  direct  attraction  to  the  positive  or  negative 
pole.  Rut  these  terms  are  much  too  significant  for  the  use  to  which  I  should 
have  to  put  them ;  for  though  the  meanings  are  perhaps  right,  they  are  only 
hypothetical,  and  may  be  wrong ;  and  then,  through  a  very  imperceptible  but 
still  very  dangerous, because  continual,  influence,  they  do  great  injury  to  science, 
by  contracting  and  limiting  the  habitual  views  of  those  engaged  in  pursuing  it. 
I  propose  to  distinguish  these  bodies  by  calling  those  anionsX  which  go  to  the 
anode  of  the  decomposing  body ;  and  those  passing  to  the  cathode ,  cations%  ; 
and  when  I  have  occasion  to  speak  of  these  together,  1  shall  call  them  ions. 
Thus,  the  chloride  of  lead  is  an  electrolyte ,  and  when  electrolyzed  evolves  the 
two  ions ,  chlorine  and  lead  —  the  former  being  an  anion ,  and  the  latter  a 
cation. 

These  terms,  being  once  well  defined,  will,  I  hope,  in  their  use  enable  me  to 
avoid  much  periphrasis  and  ambiguity  of  expression.  I  do  not  mean  to  press 
them  into  service  more  frequently  than  will  be  required,  for  I  am  fully  aware 
that  names  are  one  thing  and  science  another§. 

It  will  be  well  understood  that  I  am  giving  no  opinion  respecting  the  nature 
of  the  electric  current  now,  beyond  what  I  have  done  on  a  former  occasion  ; 
and  that  though  I  speak  of  the  current  as  proceeding  from  the  parts  which 
are  positive  to  those  which  are  negative,  it  is  merely  in  accordance  with  the 
conventional,  though  in  some  degree  tacit,  agreement  entered  into  by  scientific 
men,  that  they  may  have  a  cons  ant,  certain,  and  definite  means  of  referring 
to  the  direction  of  the  forces  of  that  current. 


*  r)\tKT pov  and  A vio  joli  o  N.  Electrolyte  ;  V.  Electrolyze, 
t  av.ov  that  71  huh  unes  up  (Neuter  participle.'  X  tcariov  that  which  goes  dotm. 

5  Since  this  paper  was  read,  I  have  changed  some  of  the  terms  which  were  first  proposed,  that  I  might 
employ  only  such  as  were  at  the  same  time  simple  in  their  nature,  clear  in  their  relerence,  and  tree 
from  hypothesis. 


348 


ELECTRICITY. 


On  a  new  Measurer  of  Volta-Electricity. 

I  have  already  said,  when  engaged  in  reducing  common  and  voltaic  elec¬ 
tricity  to  one  standard  of  measurement,  and  again  when  introducing  my  theory 
of  electro-chemical  decomposition,  that  the  chemical  decomposing  action  of 
a  current  is  constant for  a  constant  quantity  of  electricity,  notwithstanding  the 
greatest  variations  in  its  sources,  in  its  intensity,  in  the  size  of  the  electrodes 
used,  in  the  nature  of  the  conductors  (or  non-conductors)  through  which  it  is 
passed,  or  in  other  circumstances.  The  conclusive  proofs  of  the  truth  of  these 
statements  shall  be  given  almost  immediately. 

I  endeavoured  upon  this,  law  to  construct  an  instrument  which  shoul4 
measure  out  the  electricity  passing  through  it,  and  which,  being  interposed  in 


Fig.  291. 


the  course  of  the  current  used  in  any  particular  experiment,  should  serve,  at 
pleasure,  either  as  a  comparative  standard  of  effect  or  as  a  positive  measurer 
of  this  subtile  agent. 

There  is  no  substance  better  fitted,  under  ordinary  circumstances,  to  be  the 
indicating  body  in  such  an  instrument  than  water  ;  for  it  is  decomposed  with 
facility  when  rendered  a  better  conductor  by  the  addition  of  acids  or  salts ;  its 
elements  may  in  numerous  cases  be  obtained  and  collected  without  any 
embarrassment  from  secondary  action,  and,  being  gaseous,  they  are  in  the 
best  physical  condition  for  separation  and  measurement.  Water,  therefore, 
acidulated  by  sulphuric  acid,  is  the  substance  1  shall  generally  refer  to, 
although  it  may  become  expedient  in  peculiar  cases  or  forms  of  experiment 
to  use  other  bodies. 

The  first  precaution  needful  in  the  construction  of  the  instrument  was  to 
avoid  the  recombination  of  the  evolved  gases,  an  effect  which  the  positive 
electrode  had  been  found  so  capable  of  producing.  For  this  purpose  various 
forms  of  decomposing  apparatus  were  used.  The  first  consisted  of  straight 
tubes,  each  containing  a  plate  and  wire  of  platina  soldered  together  by  gold, 
and  fixed  hermetically  in  the  glass  at  the  closed  extremity  of  the  tube  (Fig. 
291).  The  tubes  were  about  8  in.  long,  07  of  an  inch  in  diameter,  and 
graduated.  The  platina  plates  were  about  an  inch  long,  as  wide  as  the  tubes 


FARADAY'S  RESEARCHES. 


349 


would  permit,  and  adjusted  as  near  to  the  mouths  of  the  tubes  as  was  con¬ 
sistent  with  the  safe  collection  of  the  gases  evolved.  In  certain  cases,  where 
it  was  required  to  evolve  the  elements  upon  as  small  a  surface  as  possible,  the 
metallic  extremity,  instead  of  being  a  plate,  consisted  of  the  wire  bent  into  the 
form  of  a  ring.  When  these  tubes  were  us?d  as  measurers,  they  were  filled 
with  the  dilute  sulphuric  acid,  and  inverted  in  a  basin  of  the  same  liquid, 
being  placed  in  an  inclined  position  (Fig.  293  a),  with  their  mouths  near  to 
each  other,  that  as  little  decomposing  matter  should  intervene  as  possible;  and, 
ilso,  in  such  a  direction  that  the  platina  plates  should  be  in  vertical  planes. 

Another  form  of  apparatus  was  that  delineated  (Fig.  292).  The  tube  is  bent 
in  the  middle;  one  end  is  closed;  in  that  end  is  fixed  a  wire  and  plate,  a,  pro¬ 
ceeding  so  far  downwards,  that,  when  in  the  position  figured,  it  shall  be  as 
near  to  the  angle  as  possible,  consistently  with  the  collection,  at  the  closed 
extremity  of  the  tube,  of  all  the  gas  evolved  against  it.  The  plane  of  this  plate 
is  also  perpendicular.  The  other  metallic  termination,  b,  is  introduced  at  the 
time  decomposition  is  to  be  effected,  being  brought  as  near  the  angle  as 
possible,  without  causing  any  gas  to  pass  from  it  towards  the  closed  end  of 
the  instrument.  The  gas  evolved  against  it  is  allowed  to  escape. 

The  third  form  of  apparatus  contains  both  electrodes  in  the  same  tube;  the 
transmission,  therefore,  of  the  electricity,  and  the  consequent  decomposition, 
is  far  more  rapid  than  in  the  separate  tubes.  The  resulting  gas  is  the  sum 
of  the  portions  evolved  at  the  two  electrodes,  and  the  instrument  is  better 


Fig.  293. 


adapted  than  either  of  the  former  as  a  measurer  of  the  quantity  of  voltaic 
electricity  transmitted  in  ordinary  cases.  1 1  consists  of  a  straight  tube  (Fig.  293) 
closed  at  the  upper  extremity,  and  graduated,  through  the  sides  of  which  pass 
the  platina  wires  (being  fused  into  the  glass),  which  are  connected  with  two 
plates  within.  The  tube  is  fitted  by  grinding  into  one  mouth  of  a  double- 
necked  .bottle.  If  the  latter  be  one-half  or  two-thirds  full  of  the  dilute 
sulphuric  acid,  it  will,  upon  inclination  of  the  whole,  flow  into  the  tube  and 
fili  it.  When  an  electric  current  is  passed  through  the  instrument,  the  gases 
evolved  against  the  plates  collect  in  the  upper  portion  of  the  tube,  and  are  not 
subject  to  the  recombining  power  of  the  platina. 


ELECTRICITY. 


35° 


Another  form  of  the  instrument  is  given  at  Fig.  294. 

A  fifth  form  is  delineated  (Fig.  295  b).  This  I  have  found  exceedingly  useful 
in  experiments  continued  in  succession  for  days  together,  and  where  large 
quantities  of  indicating  gas  were  to  be  collected.  It  is  fixed  on  a  weighted 
foot,  and  has  the  form  of  a  small  retort  containing  the  two  electrodes:  the  neck 
is  narrow,  and  sufficiently  long  to  deliver  gas  issuing  from  it  into  a  jar  placed 
in  a  small  pneumatic  trough.  The  electrode  chamber,  sealed  hermetically 
at  the  part  held  in  the  stand,  is  5  in.  in  length  and  o'6  of  an  inch  in  diameter; 
the  neck  about  9  in.  in  length,  and  o-4  of  an  inch  in  diameter  internally.  The 
figure  will  fully  indicate  the  construction. 


It  can  hardly  be  requisite  to  remark,  that  in  the  arrangement  of  any  of 
these  forms  of  apparatus,  they,  and  the  wires  connecting  them  with  the 
substance,  which  is  collaterally  subjected  to  the  action  of  the  same  electric 
current,  should  be  so  far  insulated  as  to  ensure  a  certainty  that  all  the  elec¬ 
tricity  which  passes  through  the  one  shall  also  be  transmitted  through  the 
other. 

The  equivalent  numbers  do  not  profess  to  be  exact,  and  are  taken  almost 
entirely  from  the  chemical  results  of  other  philosophers  in  whom  I  could 
repose  more  confidence,  as  to  these  points,  than  in  myself. 


TABLE  OF  IONS. 
Anions. 


Oxygen  . 

8 

Phosphoric  acid  . 

•  357 

Chlorine 

•  35‘5 

Carbonic  acid 

.  .  22 

Iodine  . 

.  126 

Boracic  acid  . 

.  24 

Bromine 

•  78-3 

Acetic  acid  . 

•  5i 

Fluorine 

.  187 

Tartaric  acid . 

.  .  66 

Cyanogen 

26 

Citric  acid 

.  .  58 

Sulphuric  acid 

40 

Oxalic  acid  . 

•  •  36 

Selenic  acid  . 

.  64 

Sulphur  (?)  . 

.  .  16 

Nitric  acid 

•  54 

Selenium  (?)  . 

Chloric  acid  . 

•  75 '5 

Sulpho-cyanogen  . 

. 

FAR  A  DA  Y'S  RESEARCHES. 


35i 


Cations. 


Hydrogen 

1 

Mercury 

200 

Potassium 

39'2 

Silver  . 

108 

Sodium  . 

23'3 

Platina  .... 

98-6? 

Lithium . 

10 

Gold  .... 

(?) 

Barium  . 

68-7 

— 

St.ontium 

43'8 

Ammonia 

17 

Calcium 

20-5 

Potassa  .... 

47 ‘2 

Magnesium 

12  *7 

Soda  .... 

31  *3 

Manganese 

277 

Lithia  .... 

18 

Zinc 

32-5 

Baryta  .... 

76-7 

Tin 

<?7‘9 

Strontia . 

51*8 

Lead 

i°3*5 

Lime  .... 

28*5 

Iron 

28 

Magnesia 

207 

Copper  . 

3r6 

Alumina 

(?) 

Cadmium 

55-8 

Protoxides  generally. 

Cerium  . 

46 

Quinia  .... 

171-6 

Cobalt  . 

29-5 

Cinchona 

160 

Nickel  . 

29-5 

Morphia 

290 

Antimony 

64-6? 

Vegeto-alkalies  generally. 

Bismuth 

7i 

Now  it  is  wonderful  to  observe  how  small  a  quantity  of  a  compound  body 
is  decomposed  by  a  certain  portion  of  electricity.  Let  us,  for  instance,  con¬ 
sider  this  and  a  few  other  points  in  relation  to  water.  One  grain  of  water, 
acidulated  to  facilitate  conduction,  will  require  an  electric  current  to  be  con¬ 
tinued  for  three  minutes  and  three-quarters  of  time  to  effect  its  decomposition, 
which  current  must  be  powerful  enough  to  retain  a  platina  wire,  1- 104th  of  an 
inch  in  thickness*,  red  hot,  in  the  air  during  the  whole  time ;  and  if  interrupted 
anywhere  by  charcoal  points,  will  produce  a  very  brilliant  and  constant  star 
of  light.  If  attention  be  paid  to  the  instantaneous  discharge  of  electricity  of 
tension,  as  illustrated  in  the  beautiful  experiments  of  Mr.  Wheatstonef,  and 
to  what  I  have  said  elsewhere  on  the  relation  of  common  and  voltaic  electri¬ 
city,  it  will  not  be  too  much  to  say,  that  this  necessary-  quantity  of  electricity 
is  equal  to  a  very  powerful  flash  of  lightning.  Yet  we  have  it  under  perfect 
command;  can  evolve,  direct,  and  employ  it  at  pleasure;  and  when  it  has 
performed  its  full  work  of  electrolyzation,  it  has  only  separated  the  elements 
of  a  single  grain  of  water. 

1  showed  in  a  former  series  of  these  Researches  on  the  relation  by  measure 
of  common  and  voltaic  electricity,  that  two  wires,  one  of  platina  and  one  of 
zinc,  each  1  - 1  Sth  of  an  inch  in  diameter,  placed  5-i6ths  of  an  inch  apart, 


*  I  h.rce  not  stated  the  length  of  wire  used.  because  I  find  fcv  experiment,  as  would  be  expected  in 
theory,  that  it  is  inuitlerent  The  same  quantity  of  electricity  which,  passed  in  a  given  time,  can  heat 
an  inch  of  platina  wire  of  a  certain  diameier  red  hot,  can  also  heat  a  hundred,  a  thousand,  or  any  length 
of  the  same  wire  to  the  same  degTee,  provided  the  cooling  circumstances  are  the  same  for  every  part  in 
both  cases.  This  1  have  proved  bv  the  volta-electrometer.  I  found  that,  whether  half-an-inch  or  8  in 
were  retained  at  one  constant  temperature  of  dull  redness,  equal  quantities  of  water  were  decomposed 
in  equal  times  in  both  cases.  When  the  half-inch  was  used,  only  the  centre  portion  of  wire  was 
ienited.  A  tine  wire  may  even  be  used  as  a  rough  hut  ready  regulator  of  a  voltaic  current ;  for  if  it  be 
made  part  of  the  circuit,  and  th  larger  wires  commuivcaiing  with  it  be  shifted*  nearer  to  or  further 
apart,  so  as  to  keep  the  portion  of  wire  in  the  cncuit  sensibly  at  the  same  temperature,  the  current 
passing  through  it  will  he  nearly  uniform.  t 

+  “  Literary  Gazette,’'  1S33,  March  i  and  8  j  “  Philosophical  Magazine,”  1835,  p.  204;  "  L  Institute, 
1&.I0,  p.  abl. 


352 


ELECTRICITY. 


and  immersed  to  the  depth  of  5~8ths  of  an  inch  in  acid,  consisting  of  one  drop 
of  oil  of  vitriol  and  4  oz.  of  distilled  water,  at  a  temperature  of  about  6o°  Fahr., 
and  connected  at  the  other  extremities  by  a  copper  wire  18  ft.  long  and  I  - 1 8th 
of  an  inch  in  thickness,  yielded  as  much  electricity  in  little  more  than  three 
seconds  of  time  as  a  Leyden  ba  tery  charged  by  thirty  turns  of  a  very  large 
and  powerful  plate  electric  machine  in  full  action.  This  quantity,  though 
sufficient  if  passed  at  once  through  the  head  of  a  rat  or  a  cat  to  have  killed  it, 
as  by  a  flash  of  lightning,  was  evolved  by  the  mutual  action  of  so  small  a 
portion  of  the  zinc  wire  and  water  in  contact  with  it,  that  the  loss  of  weight 
sustained  by  either  would  be  inappreciable  by  our  most  delicate  instruments ; 
and  as  to  the  water  which  could  be  decomposed  by  that  current,  it  must  have 
been  insensible  in  quantity,  for  no  trace  of  hydrogen  appeared  upon  the 
surface  of  the  platina  during  those  three  seconds. 

What  an  enormous  quantity  of  electricity,  therefore,  is  required  for  the 
decomposition  of  a  single  grain  of  water!  We  have  already  seen  that  it  must 
be  in  quantity  sufficient  to  sustain  a  platina  wire  I-I04th  of  an  inch  in  thick¬ 
ness,  red  hot,  in  contact  with  the  air  for  three  minutes  and  three-quarters,  a 
quantity  which  is  almost  infinitely  greater  than  that  which  could  be  evolved 
by  the  little  standard  voltaic  arrangement  to  which  1  have  just  referred.  I 
have  endeavoured  to  make  a  comparison  by  the  loss  of  weight  of  such  a  wire 
in  a  given  time  in  such  an  acid,  according  to  a  principle  and  experiment  to 
be  almost  immediately  described  ;  but  the  proportion  is  so  high,  that  I  am 
almost  afraid  to  mention  it.  It  would  appear  that  800,000  such  charges  of 
the  Leyden  battery  as  I  have  referred  to  above  would  be  necessary  to  supply 
electricity  sufficient  to  decompose  a  single  grain  of  water;  or,  if  I  am  right, 
to  equal  the  quantity  of  electricity  which  is  naturally  associated  with  the 
elements  of  that  grain  of  water,  endowing  them  with  their  mutual  chemical 
affinity. 

In  further  proof  of  this  high  electric  condition  of  the  particles  of  matter,  and 
the  identity ,  as  to  quantity ,  of  that  belonging  to  them  with  that  necessary  for 
their  separation,  I  will  describe  an  experiment  of  great  simplicity,  but  extreme 
beauty,  when  viewed  in  relation  to  the  evolution  of  an  electric  current  and  its 
decomposing  powers. 

A  dilute  sulphuric  acid,  made  by  adding  about  one  part  by  measure  of  oil 
of  vitriol  to  thirty  parts  of  water,  will  act  energetically  upon  a  piece  of  plate 
zinc  in  its  ordinary  and  simple  state;  but,  as  Mr.  Sturgeon  has  shown*,  not 
at  all,  or  scarcely  so,  if  the  surface  of  the  metal  has  in  the  first  instance  been 
amalgamated ;  yet  the  amalgamated  zinc  will  act  powerfully  with  platina  as 
an  electromotor,  hydrogen  being  evolved  on  the  surface  of  the  latter  metal,  as 
the  zinc  is  oxidized  and  dissolved.  The  amalgamation  is  best  effected  by 
sprinkling  a  few  drops  of  mercury  upon  the  surface  of  the  zinc,  the  latter 
being  moistened  with  the  dilute  acid,  and  rubbing  with  the  fingers  so  as  to 
extend  the  liquid  metal  over  the  whole  of  the  surface.  Any  mercury  in  excess, 
forming  liquid  drops  upon  the  zinc,  should  be  wiped  ofTf. 

Two  plates  of  zinc  thus  amalgamated  were  dried  and  accurately  weighed  r 
one,  which  we  will  call  A,  weighed  1 63'  1  grains;  the  other,  to  be  called  B. 
weighed  I48'3  grains.  They  were  about  5  in.  long,  and  crq  of  an  inch  wide. 


*  “Recent  Experimental  Researches,"’ &c  ,  1830,  p.  74,  &  c. 
t  The  experiment  may  he  made  with  pure  7inc,  which,  as  chemists  weli  know,  is  but  slightly  acted 
upon  by  dilute  sulphuric  acid,  in  comparison  with  ordinary  zinc,  which  during  the  action  is  subject  to 
an  infinity  ot  voltaic  actions.  See  De  la  Rive  on  this  subject,  “  Bibliothbque  Universelle,’’  1830,  p.  3£I* 


FAR  AD  A  Y'S  RESEARCHES. 


353 


An  earthenware  pneumatic  trough  was  filled  with  dilute  sulphuric  acid,  of  the 
strength  just  described,  and  a  gas  jar,  also  filled  with  the  acid,  inverted  in  it*. 
A  plate  of  platina  of  nearly  the  same  length,  but  about  three  times  as  wide  as 
the  zinc  plates,  was  put  up  into  this  jar.  The  zinc  plate  A  was  also  intro¬ 
duced  into  the  jar,  and  brought  in  contact  with  the  platina,  and  at  the  same 
moment  the  plate  B  was  put  into  the  acid  of  the  trough,  but  out  of  contact 
with  other  metallic  matter. 

Strong  action  immediately  occurred  in  the  jar  upon  the  contact  of  the  zinc 
and  platina  plates.  Hydrogen  gas  rose  from  the  platina,  and  was  collected 
in  the  jar  ;  but  no  hydrogen  or  other  gas  rose  from  cither  zinc  plate.  In  about 
ten  or  twelve  minutes,  sufficient  hydrogen  having  been  collected,  the  experi¬ 
ment  was  stopped :  during  its  progress  a  few  small  bubbles  had  appeared 
upon  plate  B,  but  none  upon  plate  A.  The  plates  were  washed  in  distilled 
water,  dried,  and  reweigned.  Plate  B  weighed  I48’3  grains,  as  before,  having 
lost  nothing  by  the  direct  chemical  action  of  the  acid.  Plate  A  weighed  I54'65 
grains,  8-45  grains  of  it  having  been  oxidized  and  dissolved  during  the  experi¬ 
ment. 

The  hydrogen  gas  was  next  transferred  to  a  water-trough  and  measured ;  it 
amounted  to  12*5  cubic  inches,  the  temperature  being  52°,  and  the  barometer 
292  inches.  This  quantity,  corrected  for  temperature,  pressure,  and  moisture, 
becomes  12T5453  cubic  inches  of  dry  hydrogen  at  mean  temperature  and 
pressure,  which,  increased  by  one-half  for  the  oxygen  that  must  have  gone  to 
the  anode ,  i.e.  to  the  zinc,  gives  18*232  cubic  inches  as  the  quantity  of  oxygen 
and  hydrogen  evolved  from  the  water  decomposed  by  the  electric  current. 
According  to  the  estimate  of  the  weight  of  the  mixed  gas  before  adopted,  this 
volume  is  equal  to  2*3535  544  grains,  which  therefore  is  the  weight  of  water 
decomposed;  and  this  quantity  is  to  8*45,  the  quantity  of  zinc  oxidized. as  9  is 
to  32*31.  Now  taking  9  as  the  equivalent  number  of  water,  the  number  325 
is  given  as  the  equivalent  number  of  zinc — a  coincidence  sufficiently  near  to 
show,  what  indeed  could  not  but  happen,  that  for  an  equivalent  of  zinc  oxidized 
an  equivalent  of  water  must  be  decomposedf. 

But  let  us  observe  how  the  water  is  decomposed.  It  is  electrolyzed,  i  e.,  is 
decomposed  voltaically,  and  not  in  the  ordinary  manner  (as  to  appearance)  of 
chemical  decompositions;  for  the  oxygen  appears  at  the  anode  and  the  hydro¬ 
gen  at  the  cathode  of  the  decomposing  body,  and  these  were  in  many  parts  of 
the  experiment  above  an  inch  asunder.  Again,  the  ordinary  chemical  affinity 
was  not  enough  under  the  circumstances  to  effect  the  decomposition  of  the 
water,  as  was  abundantly  proved  by  the  inaction  on  plate  B;  the  voltaic 
current  was  essential.  And  to  prevent  any  idea  that  the  chemical  affinity  was 
almost  sufficient  to  decompose  the  water,  and  that  a  smaller  current  of  elec¬ 
tricity  might,  under  the  circumstances,  cause  the  hydrogen  to  pass  to  the 
cathode ,  I  need  only  refer  to  the  results  which  I  have  given  to  show  that  the 
chemical  action  at  the  electrodes  has  not  the  slightest  influence  over  the 
quantities  of  water  or  other  substances  decomposed  between  them,  but  that 
they  are  entirely  dependent  upon  the  quantity  of  electricity  which  passes. 

What,  then,  follows  as  a  necessary  consequence  of  the  whole  experiment  ? 
Why,  this — that  the  chemical  action  upon  32*31  parts,  or  one  equivalent  of 


*  The  acid  was  left  during  a  night  with  a  .mall  piece  of  unamalgamated  zinc  in  it.  for  the  purpose  of 
evolving  such  air  as  might  he  inclined  to  separate,  and  bringing  the  whole  into  a  constant  state, 
t  The  experiment  was-  repeated  several  times  with  the  same  results. 

23 


354 


ELECTRICITY. 


zinc,  in  this  simple  voltaic  circle,  was  able  to  evolve  such  quantity  of  electricity 
in  the  form  of  a  current  as,  passing  through  water,  should  decompose  9  parts, 
or  one  equivalent  of  that  substance;  and,  considering  the  definite  relations  of 
electricity  as  developed  in  the  preceding  parts  of  the  present  paper,  the  results 
prove  that  the  quantity  of  electricity  which,  being  naturally  associated  with 
the  particles  of  matter,  gives  them  their  combining  power,  is  able,  when  thrown 
into  a  current,  to  separate  those  particles  from  their  state  of  combination  ;  or, 
in  other  words,  that  the  electricity  which  decomposes ,  and  that  which  is  evolved 
by  the  decomposition  oj, ’  a  certain  quantity  of  matter  are  alike. 

But  admitting  that  chemical  action  is  the  source  of  electricity,  what  an 
infinitely  small  fraction  of  that  which  is  active  do  we  obtain  and  employ  in 
our  voltaic  batteries!  Zinc  and  platina  wires,  1 -1 8th  of  an  inch  in  diameter 
and  about  half  an  inch  long,  dipped  into  dilute  sulphuric  acid,  so  weak  that  it 
is  not  sensibly  sour  to  the  tongue,  or  scarcely  to  our  most  delicate  test-papers, 
will  evolve  more  electricity  in  i-2oth  of  a  minute  than  any  man  would  willingly 
allow  to  pass  through  his  body  at  once.  The  chemical  action  of  a  grain  of 
water  upon  four  grains  of  zinc  can  evolve  electricity  equal  in  quantity  to  that 
of  a  powerful  thunder-storm.  Nor  is  it  merely  true  that  the  quantity  is  active; 
it  can  be  directed  and  made  to  perform  its  full  equivalent  duty.  Is  there  not, 
then,  great  reason  to  hope  and  believe  that,  by  a  closer  experimental  investi¬ 
gation  of  the  principles  which  govern  the  development  and  action  of  this 
subtile  agent,  we  shall  be  able  to  increase  the  power  of  our  batteries,  or  invent 
new  instruments  which  shall  a  thousandfold  surpass  in  energy  those  which  we 
at  present  possess? 

After  Faraday  had  invented  his  first  apparatus  or  volta-measurer,  other 
and  more  convenient  contrivances  were  made  by  himself  and  others. 


F IG.  296. — Large  Voltameter  for  measuring  the  quantity  of  Mixed  Gases 
obtainable  from  small  or  large  batteries. 

The  apparatus  made  by  Elliott  Brothers  consists  of  a  large  pair  of  platina- 
plate  electrodes,  doubly  folded  and  approximated  one  to  the  other,  so  as  to 
present  the  largest  amount  of  surface  for  the  liberation  of  the  mixed  gases, 
oxygen  and  hydrogen  ;  the  plates  are  contained  in  a  glass  bell  jar,  surmounted 
by  a  bent  conducting  tube  to  convey  the  gases  to  the  graduated  cylindrical 
glass  jar,  which  is  provided  with  a  stop-cock. 


GROVE'S  GAS  BATTERY. 


355 


Faraday’s  voltameter  experiment  has  been  reversed  in  the  most  philosophi¬ 
cal  manner  by  Professor  Grove,  who  partly  filled  fifty  tubes  alternately  with 
oxygen  and  hydrogen.  The  tubes  each  contained  a  plate  of  platinum  roughened 
with  a  deposit  of  black  platinum  powder  upon  them,  and,  when  connected 
as  in  Fig.  297,  they  produced  a  current  which  afforded  all  the  ordinary  elec¬ 
trical  results.  The  tubes  are  partly  filled  with,  and  stand  in  glass  jars  con¬ 
taining,  dilute  sulphuric  acid,  specific  gravity  rcoo,  and,  when  placed  on  a 
stool  supported  on  glass  legs,  give  a  shock  which  can  be  felt  by  five  persons, 


affected  the  electroscope  and  the  galvanometer  needle,  gave  an  electi  ic  spark, 
and  decomposed  water,  iodide  of  potassium,  &c.  This  beautiful  experiment 
proved  that  just  as  the  current  of  electricity  decomposed  water  into  oxygen  and 
hydrogen  (Fig.  298),  so  the  same  gases  properly  disposed,  as  in  Fig.  299,  would 
reunite,  and,  in  the  act  of  reunion,  evolve  a  current  of  electricity  that  would 
again  repeat  itself  in  the  production  of  all  those  phenomena  already  detailed 


Fig.  299. —  Class  Cell  with  cardboard  Diaphragm  for  Chemical  Decomposition. 


When  the  poles  of  the  battery,  usually  platinum  plates,  are  immersed  in  a 
glass  cell,  divided  in  the  centre  with  a  slip  of  card,  and  filled  with  a  solution 
of  iodide  of  potassium  and  starch,  electrolytic  decomposition  occurs;  the 
iodine  is  liberated  on  one  side,  and,  combining  with  the  starch,  produces  a 
purple  colour,  whilst  the  other  side  remains  colourless  because  the  alkali  is 
there  liberated  and  has  no  action  upon  the  starch.  If,  however,  a  little  tinc¬ 
ture  of  turmeric  is  carefully  dropped  in  and  mixed,  it  turns  a  reddish  brown, 

23 — 2 


356 


ELECTRICITY. 


and  thus  indicates  the  presence  of  the  potassium  oxidized  and  changed  to 
potash  in  the  presence  of  water. 

A  number  of  amusing  chemical  decompcsitions  may  be  performed  with  the 
same  arrangement.  A  very  good  one  is  that  in  which  a  solution  of  common 
salt  and  indigo  is  used.  The  liberation  of  chlorine  at  one  pole  causes  the 
half  of  the  contents  of  the  trough  to  be  bleached,  the  other  remaining  a 
blue  colour. 

When  iodide  of  potassium  or  chloride  of  sodium  yield  their  elements  to 
the  pou’er  of  the  circulating  electricity,  such  and  other  similar  cases  are  called 
“ primary  results.”  But  when  metals  are  reduced,  as  already  mentioned,  the 
nascent  hydrogen  and  the  oxide  of  the  metal  are  deposited  together,  and 
the  former,  reacting  on  the  latter,  deoxidizes  the  oxide,  and  reduces  it  to  the 
metallic  state.  It  is  thus  we  have  the  art  of  electrotyping,  already  alluded 
to  at  page  313,  and  such  a  decomposition  would  be  called  a  “ secondary  result. 1 


Fig.  300. 


The  above  are  two  arrangements  of  a  Daniell’s  single  cell  and  trough,  con¬ 
taining  the  solution  of  sulphate  of  copper  and  the  various  seals,  casts,  &c., 
which  are  to  be  copied  by  the  deposit  of  metallic  copper  upon  them.  In  one, 
the  Daniell’s  cell  is  connected  with  a  trough ;  in  the  other,  the  cell  itself,  zinc, 
acid,  and  the  medals  to  be  copied  in  the  sulphate  of  copper,  perform  the  same 
functions. 


Ohm's  Law. 


In  the  admirable  and  exhaustive  work  on  the  electric  telegraph,  Mr.  Robert 
Sabine  says : 

“  Until  the  end  of  the  first  quaiter  of  the  present  century,  physicists  were 
still  in  darkness  as  to  the  mode  and  laws  of  the  propagation  of  the  galvanic 
current.  The  immense  velocity  with  which  the  galvanic  impulse  is  transmitted 
led  to  the  seeking  an  analogy  between  it  and  light,  and  on  this  wrong  scent 
much  time  and  labour  was  lost;  when  Ohm,  a  German  physicist,  conceived 
the  happy  idea  that  a  juster  analogy  was  to  be  found  in  the  propagation  of  heat, 
and  proceeded  to  apply  to  galvanic  electricity  the  formulae  of  Founder  and 
Poisson.  He  expressed  the  intensity  of  an  electric  current  as  directly  pro¬ 
portional  to  the  electro-motive  force,  and  inversely  to  the  resistance  ot  the 
circuit.  Algebraically,  if  E  is  the  electro-motive  force,  R  the  resistance,  and 
I  the  intensity, 


E 


(I- 


OHM'S  LAW. 


357 


“Of  these  magnitudes,  R  is  made  up  of  two  resistances — that  interior  and  that 
exterior  of  the  element.  The  internal  resistance,  or  resistance  of  the  element,  is 
again  the  sum  of  the  several  resistances  due  to  the  passage  of  the  current  from 
one  plate  to  the  liquid,  to  its  passage  through  the  liquid,  and  from  its  passage 
from  the  liquid  to  the  other  plate.  We  will  call  this  resistance  of  the  element  r. 
The  remaining  component,  the  external  resistance,  is  that  due  to  the  passage 
of  the  current  through  the  interiors  of  the  plates,  the  wire  connecting  them, 
and  through  whatever  conductor  may  be  otherwise  inserted  between  them. 
Let  this  be  p.  Substituting  these  values  for  R  in  (I. 


F, 


“  The  truth  of  this  equation  may  be  proved  experimentally  as  follows : 

“  Evidence  of  the  direct  proportion  of  the  intensity  to  the  electro  motive 
force  is  obtained  by  comparing  the  known  function  of  the  deflections  of  a  mag¬ 
netic  needle  of  a  galvanometer,  due  to  a  current  in  a  circuit,  in  which  rand  p, 
the  circuit  resistances,  remain  constant,  while  the  numbers  of  pairs  are  changed. 
The  resistance  r  of  a  pair  of  plates  of  equal  surface  at  the  same  distance 
diminishes  as  their  surface  is  increased,  and  vice  versa;  but  the  resistance  of 
more  pairs  joined  up  in  series  increases  proportionally  to  the  number.  There¬ 
fore  we  take  a  single  pair  of  plates  of  known  surface,  and  connect  them  in  the 
circuit  of  a  galvanometer,  and  of  a  length  of  wire,  determined  by  a  rhecord 
or  other  adjustible  resistance,  and  note  the  deflection  (f)u.  Then  we  double  the 
electro-motive  force  E  by  inserting  in  the  place  of  these  two  pairs  of  plates  of 
each,  double  the  surface  of  the  former,  by  which  the  resistance  r  remains  un¬ 
changed.  The  wire  p  remains  also  the  same;  but  we  have  another  deflec¬ 
tion,  (f)u  For  the  intensity  1  with  the  single  pair  we  have  the  expression — 


j)  .  .  I  =  F(<£°) 


and  with  the  second  reading  by  the  two  pairs — 


E 

p+r 


2) 


W>‘)  = 


2  E 
p+r 


F  being  the  function,  sine,  tangent,  or  whatever  it  may  be,  which  connects 
degrees  of  arc  with  those  of  force.  From  these  two  equations  it  follows,  and 
will  also  be  found,  that 

F  (</>!)  =  2  F 
1  =  2  I 


“  The  same  method  of  experimental  proof  may  be  extended  to  n  elements, 
connected  in  series,  by  increasing  the  surfaces  n  times.  The  remaining  relation 
expressed  by  Ohm’s  law,  that  of  current  and  resistance,  is  proved  experimen¬ 
tally  by  obtaining  a  deflection  c£,,  with  a  certain  inserted  resistance  p,  and 
electromotive  force  E,  and  then  doubling  the  length  of  the  wire  p,  diminishing 
the  size  of  the  plates  to  half,  and  doubling  their  distance  from  each  other,  by 
which  the  total  resistance  of  the  circuit  is  doubled,  while  the  electro-motive 
force  remains  the  same,  and  the  needle  is  deflected  a  smaller  angle  <f> i. 
Expressed  algebraically,  the  first  observation  gives 


I  =  F  (<£0)  = 


E 

r+p 


i) 


353 


ELECTRICITY. 


and  the  second 


2) 

from  which  it  follows  that 


Ii=F  (0?)  = 


E 

2p-j-2  r 


F  (0°)  =  2F  (<£?) 
1  =  2  I, 


which  will  be  verified  by  reducing  the  reflections  to  degrees  of  force.  A  law, 
upon  which  the  truth  of  these  results  depends,  has  yet  to  be  proved.  It  is  that 
the  resistance  is  reciprocal,  and  the  intensity  thereof  directly  proportional  to 
the  surface  of  the  plate  and  to  the  section  of  the  conductor.  If  the  plates  be 
first  immersed  a  known  fraction  of  their  surface  in  the  solution,  and  after¬ 
wards  other  fractions  and  completely,  and  at  the  same  time  the  sectional  area 
of  the  conductor  be  similarly  increased,  by  taking  thicker  wire  or  two  or  more 
wires  of  the  same  length  and  diameter  parallel  to  each  other,  the  intensity,  as 
indicated  by  the  functions  of  the  galvanometer,  will  be  found  to  increase, 
other  things  being  equal,  as  the  section  of  the  conductor  and  surface  of  the 
exciting  plates  increase.  The  application  of  Ohm’s  law  in  the  solution  of 
different  problems  which  the  electrician  finds  it  necessary  to  answer  is  very 
extended;  it  forms,  in  fact,  the  basis  upon  which  all  exact  inquirv  in  elec¬ 
trical  science  is  built  up.  We  will  see  now,  as  an  instance,  what  it  affords  us 
when  we  combine  elements  together  in  different  ways. 

“  When  the  poles  of  a  pair  of  plates  are  joined  together,  the  intensity,  I,  of 

£ 

the  current  passing  in  every  section  of  the  current  is  1=  — — .  There  are  two 

r  -rp 

principal  ways  in  which  a  number  of  galvanic  pairs  maybe  connected  together, 
ist.  They  may  be  connected  in  series  for  intensity,  so  as  to  add  their  electro¬ 
motive  forces  and  resistances  together;  and  (2nd)  they  may  be  connected 
parallel  to  each  other  (or  quantity,  as  it  is  called,  so  that  the  electro-motive 
force  of  the  combination  remains  the  same;  but  the  surfaces  of  the  plates  are 
increased,  and  hence  the  resistance  in  the  same  measure  diminished.  First, 
let  n  elements  be  connected  thus  •  the  negative  pole  of  the  first  element  is 
joined  to  the  positive  pole  of  the  seco  nd,  the  negative  pole  of  the  second  to 
the  positive  pole  of  the  third,  and  so  on,  up  to  the  //th  element.  We  have  then 
what  is  vulgarly  called  an  ‘intensity  battery,’  and  the  intensity  of  each  indi¬ 
vidual  element  of  the  series,  if  they  are  of  the  same  size  and  kind,  will  be 


E  _  E 

p+r  +  (« — 1)  r  o+u  r 
and  that  of  the  whole  battery 

t  E 

1  »-n  -  —  . 

p  +  «  r 


(ill. 


(IV. 


When  the  resistance,  n  r ,  of  the  battery  is  so  small  in  comparison  with  p,  that 
we  can,  without  appreciable  error,  neglect  it,  the  intensity  of  the  whole  battery 
becomes 


That  is  to  say,  that  when  the  resistance  of  the  battery  is  very  small  in  com¬ 
parison  with  the  resistance  of  the  circuit  exterior  to  the  battery,  the  strength 


THE  THE  OS  TAT  OF  WHEATSTONE. 


359 


of  the  current  is  increased  in  direct  proportion  to  the  number  of  elements 
added  to  it.  Dividing  both  numerator  and  denominator  of  the  above  fraction 
(iv.)  by  the  number  of  elements,  n,  we  get 


which  becomes,  if  we  set  p  =  o, 
_ E 

In  —  -  .  . 

r 


(vi. 


affording  us  light  upon  another  relation  of  the  galvanic  current,  viz.,  that  when 
the  resistance  exterior  to  the  battery  is  so  small  that  it  may  be  neglected,  the 
current  of  a  number  of  elements  will  do  more  work  than  that  of  a  single  pair. 

“  The  first  of  these  laws  applies  to  a  battery  used  for  working  a  long  line  of 
telegraph,  whose  resistance  with  the  coils  of  the  apparatus  is  very  great  in 
comparison  to  that  of  the  element,  and  where  it  is  evident  that  a  large  battery 
is  necessary. 

“The  second  law  applies  to  a  local  circuit,  where  the  resistance  of  the  cir¬ 
cuit  is  small,  and  a  few  elements  do  as  well  as  a  great  number.” 


The  Rheostat  of  Wheatstone. 

The  Rheostat,  or  Current  Regulator.—  We  print  from  the  memoirs  of  Sir 
Charles  Wheatstone,  in  the  Transactions  of  the  Royal  Society,  “An  account 
of  several  new  instruments  and  processes  for  determining  the  Constants  of  a 
Voltaic  Circle.”  This  most  distinguished  philosopher  says  : 

“The  instruments  and  processes  I  am  about  to  describe  being  all  founded 
on  the  principles  established  by  Ohm  in  his  theory  of  the  voltaic  circuit,  and 
this  beautiful  and  comprehensive  theory  being  not  yet  generally  understood 
and  admitted,  even  by  many  persons  engaged  in  original  research,  I  could 
scarcely  hope  to  make  my  descriptions  and  explanations  understood  without 
prefacing  them  with  a  short  account  of  the  principal  results  which  have  been 
deduced  from  it. 

“  It  will  soon  be  perceived  how  the  clear  ideas  of  electro-motive  forces  and 
resistances,  substituted  for  the  vague  notions  of  intensity  and  quantity,  which 
have  been  so  long  prevalent,  enable  us  to  give  satisfactory  explanations  of 
most  important  phenomena,  the  laws  of  which  have  hitherto  been  involved  in 
obscurity'  and  doubt.  Viewing  the  laws  of  the  electric  circuit  from  the  point 
at  which  the  labours  of  Ohm  has  placed  us,  there  is  scarcely  any  branch  of 
experimental  science  in  which  so  many  and  such  various  phenomena  are 
expressed  by  formulas  of  such  simplicity  and  generality.  In  most  of  the 
physical  sciences,  the  facts  of  obser\ration  and  experiment  have  kept  pace 
yvith  theoretical  generalization.  In  this  science  alone  they  had  gone  on  accu¬ 
mulating  in  prolific  abundance  without  any  successful  attempt  having  been 
made  to  reduce  them  to  mathematical  expression.  But  this  is  no\y  happily 
effected  ;  and  what  has  hitherto  been  mere  matter  of  speculative  conjecture  is 
removed  into  the  domain  of  positive  philosophy. 

“  By  electro-motive  force  is  meant  the  cause  which,  in  a  closed  circuit, 
originates  an  electric  current,  or,  in  an  unclosed  one,  gives  rise  to  an  elcctro- 
scopic  tension.  By  resistance,  is  signified  the  ol  s  acle  opposed  to  the  passage 


36° 


ELECTRICITY. 


of  the  electric  current  by  the  bodies  through  which  it  has  to  pass;  it  is  the 
inverse  of  what  is  usually  called  their  conducting  power.  When  the  activity 
of  any  portion  of  the  circuit  is  increased  or  diminished,  either  by  a  change  in 
the  electro-motive  force  or  in  the  resistance  of  that  portion,  the  activity  of  all 
the  other  parts  of  the  circuit  increases  or  decreases  in  a  corresponding  degree ; 
so  that  the  same  quantity  of  electricity  always  passes  in  the  same  instant  of 
time  through  every  transverse  section  of  the  circuit.  The  force  of  the  current 
is  directly  proportional  to  the  sum  of  the  electro-motive  forces  which  are 
active  in  the  circuit,  and  inversely  proportional  to  the  total  resistance  of  all 
its  parts,  or,  in  other  words,  the  force  of  the  current  is  equal  to  the  sum  of  the 
electro-motive  forces  divided  by  the  sum  of  the  resistances. 

******** 

“  It  is  seldom  that  any  real  advance  is  made  in  a  scientific  theory  without 
a  corresponding  change  in  its  terminology  being  required.  Now  that  it  is 
proved,  beyond  doubt,  that  the  various  sources  of  continued  electric  action 
differ  from  each  other  only  in  the  amount  of  their  electro-motive  forces, 
modified  by  the  resistances  of  the  circuit  of  which  they  form  a  part,  it 
becomes  of  importance,  in  order  to  give  precision  to  our  statements,  and  to 
avoid  circumlocutions  otherwise  inevitable,  to  adopt  general  terms  to  express 
the  source  of  a  current,  without  reference  to  the  peculiar  mode  of  its  produc¬ 
tion.  I  shall,  therefore,  employ  the  word  ‘rheometer’  to  denote  any  apparatus 
which  originates  an  electric  current,  whether  it  be  a  voltaic  current  or  a  voltaic 
battery,  a  thermo-electric  battery,  or  any  other  source  whatever  of  an  electric 
current.  When  speaking  of  a  single  element,  I  shall  term  it  a  rheomotive 
element ;  and  what  is  usually  called  a  voltaic  or  thermo-electric  pile  or  battery 
I  shall  term  a  rheomotive  series.  I  shall  still  use  the  ordinary  expressions 
when  I  have  to  refer  to  the  specific  sources  of  the  productions  of  electric 
currents;  but  when  I  employ  the  general  terms,  they  must  be  understood  to 
apply  to  all  these  sources  indifferently.  The  want  of  a  general  term  to  desig¬ 
nate  an  instrument  to  measure  the  force  of  an  electric  current,  without  refer¬ 
ence  to  its  particular  construction,  has  been  long  felt.  I  shall  use  the  word 
rheometer  for  this  purpose,  continuing  occasionally  to  employ  galvanometer, 
voltameter,  Sic.,  to  distinguish  the  particular  instruments  to  which  these 
names  have  been  applied — though,  perhaps,  the  terms  magnetic,  chemical, 
calorific,  &c.,  rheometer  would  be  more  appropriate. 

“  This  may  be  the  proper  place  to  explain  a  few  other  terms,  which  I  have 
frequent  occasion  to  use,  though  not  in  the  course  of  the  present  communica¬ 
tion.  By  rheotome  is  meant  an  instrument  which  periodically  interrupts  a 
current;  and  by  rheotrope,  an  instrument  which  alternately  inverts  it.  A 
rheoscope  is  an  instrument  for  ascertaining  merely  the  existence  of  an  electric 
current.  The  word  rheostat  will  be  explained  hereafter. 

“  I  have  not  introduced  these  terms  (which  will  be  found  greatly  convenient, 
and  will  enable  us  to  state  general  propositions  much  more  clearly)  without 
good  authority.  The  word  ‘  rheophore  ’  was  employed  by  Ampere  to  designate 
the  connecting  wire  of  a  voltaic  apparatus  as  being  the  carrier  or  transmitter 
of  the  current;  and  the  word  ‘rheometer,’  first  proposed  by  Peclet  as  a 
synonym  for  galvanometer,  has  been  generally  adopted  by  the  French 
writers  on  physics. 

“  The  method  of  obtaining  the  constants  of  a  rheophoric  circuit,  adopted  by 
Fechner,  Lenz,  Pouillet,  &c.,  in  their  experimental  verifications  of  Ohm’s  . 
theory,  is  essentially  the  following:  The  resistance  of  a  circuit  is  determined 


THE  EHE  OS  TAT  OF  WHEATSTONE. 


361 


c 


Fig.  301. 


by  observing  the  force  of  the  current  first,  without  any  extra-interposed  resist¬ 
ance  in  the  circuit;  and  afterwards,  when  a  known  resistance  is  added. 
The  principle  of  this  method  is  extremely  simple;  but  the  difficulty  of 
determining  immediately  the  force  of  a  current  by  means  of  a  galvanometer 
is  an  obstacle  to  its  general  employment.  Fechner  measured  the  force  of  the 
current  by  the  number  of  oscillations  of  the  needle  when  placed  at  right 
angles  to  the  coils — a  very  tedious  operation ;  and  others  have  employed  the 
deviation  of  the  needle,  the  corresponding  degrees  of  force  having  been 
previously  determined  by  some  peculiar  process,  or  inferred  from  some  rule 
depending  on  the  particular  construction  of  the  instrument.  Another  impedi¬ 
ment  to  the  use  of  the  galvanometer,  to  measure  the  force  of  a  current,  arises 
from  the  changes  in  the  magnetic  intensity  of  the  needle,  which  frequently 
occur,  especially  when  it  has  been  acted  upon  by  too  strong  a  current. 

“  The  principle  of  my  method  is  that  of  employing  variable,  instead  of  con¬ 
stant,  resistances,  bringing  thereby  the  currents  in  the  circuits  compared  to 
equality,  and  inferring  from  the  amount  of  the  resistance  measured  out 
between  two  deviations  of  the  needle  the  electro-motive  forces  and  resistances 
of  the  circuit  according  to  the  particular  conditions  of  the  experiment.  1  his 
method  requires  no  knowledge  of  the  forces  corresponding  to  different  devia¬ 
tions  of  the  needle.  To  apply  this  principle,  it  is  requisite  to  have  a  means 
of  varying  the  interposed  resistance,  so  that  it  may  be  gradually  changed 
within  any  required  limits.  I  have  contrived  two  instruments  fi  r  effecting 
this  purpose — one  intended  for  circuits  in  which  the  resistance  is  considerable, 
the  other  for  circuits  where  the  resistance  is  small. 

“The  first  instrument  is  represented  in  Pig.  301  A  :  g  is  a  cylinder  of  woed, 
and  h  is  a  cylinder  of  brass,  both  of  the  same  diameter,  and  having  their  axes 
parallel  to  each  other;  on  the  w'ood  cylinder  a  spiral  groove  is  cut,  and  at  one 
of  the  extremities  a  brass  ring  is  fixed,  to  which  is  attached  one  of  the  ends  of 
a  long  wire  of  very  small  diameter,  which,  when  coiled  round  the  wood 
cylinder,  fills  the  entire  groove,  and  is  fixed  to  its  ether  end— to  the  remote 
extremity  of  the  brass  cylinder.  Two  springs,  j  and  k,  pressing  one  against 
the  brass  ring  on  the  wood  cylinder  and  the  other  against  the  extremity  of 


362 


ELECTRICITY. 


the  brass  cylinder  h ,  are  connected  with  two  binding  screws  for  the  purpose 
of  receiving  the  wires  of  the  circuit.  The  movable  handle  m  is  for  turning 
the  cylinders  on  their  axes.  When  it  is  placed  on  the  cylinder  h,  and  is  turned 
to  the  right,  the  wire  is  uncoiled  from  the  wood  cylinder  and  coiled  on  the 
brass  cylinder  ;  but  when  it  is  applied  to  the  cylinder  g,  and  is  turned  to  the 
left,  the  reverse  is  effected.  The  coils  on  the  wood  cylinder  being  insulated 
and  kept  separate  from  each  other  by  the  groove,  the  current  passes  through 
the  entire  length  of  wire  coiled  upon  that  cylinder ;  but,  the  coils  in  the  brass 
cylinder  not  being  insulated,  the  current  passes  immediately  from  the  point  of 
the  wire  which  is  in  contact  with  the  cylinder  to  the  spring  k;  the  effective 
part  of  the  length  of  the  wire  is,  therefore,  the  variable  portion  that  is  on  the 
wood  cylinder. 

“  In  the  instrument  I  usually  employ,  the  cylinders  are  6  in.  in  length  and 
1 1  in.  in  diameter;  the  threads  of  the  screw  are  forty  to  the  inch;  and  the 
wire  is  of  brass,  i-iooth  of  an  inch  in  diameter.  I  employ  a  very  thin  wire 
and  a  badly  conducting  metal  in  order  that  I  may  introduce  a  greater  resist¬ 
ance  into  the  circuit.  A  scale  is  placed  to  measure  the  number  of  coils 
unwound ;  and  the  fractions  of  a  coil  are  determined  by  an  index  which  is 
fixed  to  the  axis  of  one  of  the  cylinders,  and  points  to  the  divisions  of  a 
graduated  circle. 

‘‘As  tire  principal  use  of  this  instrument  is  to  adjust  or  regulate  the  circuit, 
so  that  any  constant  degree  of  force  may  be  obtained,  I  have  called  it  a 
rheostat.  Fig.  301  shows  the  arrangement  of  the  circuit  when  prepared  for 
an  experiment ;  B  is  a  delicate  galvanometer  with  an  astatic  needle,  furnished 
with  a  microscope  for  reading  off  the  divisions  of  the  circle,  which  greatly 
facilitates  the  observations  ;  C  is  the  rheomotor. 

‘•The  rheostat  which  I  employ  for  circuits  in  which  the  resistance  is  com¬ 
paratively  small  is  represented  at  Fig.  302.  a  is  a  cylinder  of  well-seasoned 
wood,  on  the  surface  of  which  a  spiral  groove  is  cut.  A  thick  copper  wire  is 
wound  round  the  cylinder,  occupying  the  groove,  forming,  as  it  were,  the  thread 
of  the  screw.  Immediately  above  the  cylinder,  and  parallel  with  its  axis,  is 
a  triangular  metal  bar,  b,  carrying  a  rider  or  slide,  c  ;  to  this  rider  a  spring,  d, 
is  fixed,  which  constantly  presses  against  the  spiral  wire,  yielding  to  any 
slight  inequality.  One  end  of  the  spiral  wire  is  attached  to  a  brass  ring,  e,  | 
against  which  a  spring,/,  presses,  which  is  connected  by  means  of  a  binding- 
screw  to  one  end  of  the  circuit  -  the  other  end  ot  the  circuit  is  held  by  the  ! 
binding-screw  which  is  in  nutation  with  the  triangular  metal  bar.  On  turn-  i 
ing  the  handle  h ,  the  cylinder  is  caused  to  move  on  its  axis  in  either  direction  ;  ' 
and  the  rider  c ,  guided  by  the  wire,  moves  along  the  bar,  advancing  or  re-  j 
ceding  according  as  the  cylinder  is  moved  right  or  left.  The  rider  coming  in 
contact  with  a  different  poi  t  of  the  spiral  wire,  a  different  resistance  is  intro-  i 
duced  into  the  circuit,  consisting  of  that  portion  of  the  wire  only  which  is  ; 
included  between  the  rider  and  the  end  of  the  wire  connected  with  the  spring/. 

“The  cylinder  of  the  instrument  I  have  constructed  is  io|  in.  in  length 
and  3j  in.  in  diameter:  the  wire  is  of  copper,  1  - 1 6th  of  an  inch  thick  ;  and 
it  makes  roS  coils  round  the  cylinder.  The  dimension  of  the  instrument,  and 
the  thickness,  length,  and  material  of  the  wire,  may  be  varied  according  to 
the  limits  of  the  variable  resistance  required  to  be  introduced  into  the  circuit,  1 
and  the  degree  of  accuracy  with  which  those  changes  are  required  to  be 
measured. 

“Fig.  302  represents  the  arrangement  of  a  thermo  electric  circuit  in  which 


THE  RHEOSTAT  OE  WHEATSTONE.  363 


Fig.  302. 


this  instrument  is  interposed.  C  is  the  thermo-electric  element ;  R,  the  gal¬ 
vanometer,  which  in  this  case  must  not  have  numerous  coils  of  tine  wire,  as 
in  the  preceding  arrangement — for  this  would  introduce  too  great  a  resistance 
in  the  circuit --but  must  consist  of  a  single  thick  plate  or  wire,  making  a  single 
convolution;  or,  which  I  think  is  preferable,  the  method  of  diverting  a  portion 
of  the  current  from  the  wire  of  a  delicate  galvanometer  described  may  be 
adopted.  Any  rheometer  in  which  the  resistance  is  small  may  be  employed 
in  conjunction  with  this  form  of  the  rheostat,  instead  of  a  thermo-electro  ele¬ 
ment  described.  The  rheostat,  especially  under  the  form  last  described,  may 
be  usefully  employed  as  a  regulator  of  a  voltaic  current,  in  order  to  maintain 
for  any  required  length  of  time  precisely  the  same  degree  of  force,  or  to  change 
it  in  any  desired  proportion.  Interposed  in  the  circuit  of  an  electro-magnetic 
engine,  however,  the  rheometer  may  vary  in  its  energy ;  the  same  velocity  may 
be  constantly  restored  by  turning  the  cylinder  of  the  regulator  to  the  left  or  to 
the  right,  according  as  the  velocity  increases  or  decreases;  or  any  different 
velocity,  within  given  limits,  may  be  obtained  by  adjusting  the  rheostat  accord¬ 
ingly. 

*»*■*£■  *  -s  *  * 

“It  is  of  the  highest  importance  to  have  a  correct  standard  of  resistance, 
and  one  that  can  easily  be  reproduced  for  the  purpose  of  comparison.  A 
copper  wire  of  a  given  length  and  diameter  might  be  employed ;  but,  as  very 
small  differences  of  diameter  are  attended  with  considerable  difierences  in  the 
resistances  of  wires,  it  is  more  convenient  to  assume  for  the  unit  of  resistance 
a  wire  of  a  given  length  and  weight,  which  allows  small  differences  to  be  very 
accurately  determined. 

“  It  is  frequentl)  required  to  measure  resistances  much  greater  than  can  be 
sheeted  by  means  of  the  rheostat,  though  the  reduced  length  of  its  wire  is 


ELECTRICITY. 


36  4 


considerable.  I  may  wish  to  know,  for  instance,  the  resistance  of  the  wire  of 
the  electro-magnets  of  my  telegraphic  apparatus,  which  is  sometimes  many 
hundred  yards  in  length,  or  that  afforded  by  an  extensive  telegraphic  line,  or 
the  resistance  of  a  certain  extent  of  an  imperfectly  conducting  liquid.  In  all 
these  cases,  and  a  variety  of  others,  I  employ  another  instrument,  which  enables 
me  to  interpose  in  the  circuit  resistances  to  any  amount,  and  yet  to  obtain  by 
the  compound  use  of  the  rheostat,  which  serves,  in  its  fine  adjustment,  any 
required  degree  of  accuracy.  This  instrument  is  represented  at  Fig.  301.  It 
consists  of  six  coils  of  fine  silk-covered  copper  wire,  about  the  1  -200th  part  of 
an  inch  in  diameter:  two  of  these  coils  are  50  ft.  in  length;  the  others  are  re¬ 
spectively  ioo,  200,  400,  and  800  ft.  in  length.  The  two  ends  of  each  coil  are 
attached  to  short  thick  wires,  fixed  to  the  upper  faces  of  the  cylinders,  which 
serve  to  combine  all  the  coils  in  one  continued  length.  The  two  wires,  a,  b , 
form  the  extremities  of  the  coils  by  which  they  are  united  to  the  circuit.  On 
the  upper  face  of  each  cylinder  is  a  double  brass  spring,  movable  round  a 
centre,  so  that  its  ends  may  rest  at  pleasure  either  on  the  ends  of  the  thick 
connecting  wires,  or  may  be  removed  from  them  and  rest  only  on  the  wood. 

In  the  latter  condition  the  current  of  the  circuit  must  pass  through  the  coil; 
but  in  the  former  position  the  current  passes  through  the  spring,  and  removes  ; 
the  resistance  of  the  coil  from  the  circuit.  When  all  the  springs  rest  on  the  i 
wires,  the  resistance  of  the  whole  series  of  coils  is  removed;  but,  by  turning  : 
the  springs  so  as  to  introduce  different  coils  into  the  current,  any  multiple  I 
of  50  feet  up  to  1600  may  be  brought  into  it. 

“  As  the  measurement  of  these  long  lengths  of  wire  cannot  be  accurately 
depended  upon,  it  is  advisable  to  ascertain  the  number  of  units  of  resistance  j 
in  each  coil,  which,  with  the  aid  of  the  rheostat,  may  be  easily  effected.  I  i 
find  the  resistance  of  the  entire  1,600  feet  to  be  equivalent  to  218,880  units  of  : 
resistance,  or  feet  of  the  standard  wire.  I  occasionally  employ  an  auxiliary  ; 
series  of  coils,  combined  in  the  same  wav  as  the  preceding,  consisting  of  six  I 
coils  of  the  same  wire,  each  500  yards  in  length.  The  reduced  length  of  this  j 
series  is  above  233  miles  of  the  standard  wire.  By  combining  it  with  the  pre-  1 
ceding,  I  am  able  to  measure  resistances  equal  to  274!  miles. 

#**##**** 


“The  rheostat  affords  a  most  ready  means  of  ascertaining  the  sum  of  the 
electro-motive  forces  active  in  a  voltaic  circuit,  without  requiring  for  this  pur¬ 
pose  the  aid  of  a  rheometer  graduated  to  indicate  proportional  forces,  or 
having  recourse  to  the  tedious  process  of  counting  the  oscillations  of  a  needle, 
employed  by  Fechner  in  his  investigations.  To  save  time  and  tro  lble  in  this 
operation  will  be  of  great  importance  to  the  future  progress  of  electro-chemistry, 
on  account  of  the  great  number  of  experiments  of  this  kind  which  yet  remain 
to  be  made,  and  also  from  the  fluctuations  in  the  electro-motive  forces  of  many 
circuits,  from  chemical  and  other  actions,  which  render  observations  requiring 
considerable  time  valueless. 

“The  principle  of  my  process  is  as  follows: — In  two  circuits  producing 
equal  rheometric  effects,  the  sum  of  the  electro-motive  forces  divided  by  the 

E  11  Yj 

resistances  is  a  constant  quantity,  /.<?.,  ;  if  E  and  R  be  proportionately 

increased  or  diminished,  F  will  obviously  remain  unchanged.  Knowing,  there¬ 
fore,  the  proportion  of  the  resistances  in  two  circuits  producing  the  same  effect, 
we  are  able  immediately  to  infer  that  of  the  electro-motive  forces. 


CALORIFIC  EFFECTS. 


365 


“  But  as  it  is  difficult  in  many  cases  to  determine  the  total  resistance,  con¬ 
sisting  of  the  partial  resistance  of  the  rheometer  itself,  the  galvanometer,  the 
rheostat,  &c.,  J  have  recourse  to  the  following  simple  process: — Increasing 
the  resistance  of  the  first  circuit  by  a  known  quantity,  r,  the  expression  becomes 

£ 

— — .  In  order  that  the  effect  in  the  second  circuit  shall  be  rendered  equal 

R+r 

to  this,  it  is  evident  that  the  added  resistance  must  be  multiplied  by  the  same 
factor  as  that  by  which  the  electro-motive  forces  and  original  resistances  are 
E  11  £ 

multiplied:  for  — — - ; — — .  The  relations  of  the  lengths  of  the  added 

r  r  r  n  R-f-/z  r 

resistances  r  and  n  r.  which  are  known,  immediately  give  those  of  the  elec¬ 
tro-motive  forces.  Experimentally,  I  proceed  thus. — 1  interpose  the  rheostat 
and  the  galvanometer  in  the  circuit,  and  then  add  by  means  of  the  former, 
assisted  if  necessary  by  the  resistance  coils,  a  sufficient  resistance  to  bring 
the  needle  exactly  450.  I  then  ascertain  the  length  of  wire  uncoiled  from  the 
brass  cylinder  of  the  regulator  necessary  to  reduce  the  deviation  of  the  needle 
to  40”.  The  number  of  turns  is  the  measure  of  the  electro-motive  force,  the 
number  corresponding  to  that  of  a  standard  element  having  been  previously 
determined.” 

The  description  of  Sir  Charles  Wheatstone’s  differential-resistance  measurer 
will  be  found  in  the  article  on  the  Telegraph,  under  the  name  of  “Wheat¬ 
stone's  British  Association  Bridge.” 

The  Calorific  Effects  of  the  Voltaic  Current. 

When  the  poles  of  the  battery,  or  rather  the  terminal  wires,  are  connected 
with  the  arms  of  the  universal  discharger,  to  which  crayon-holders,  containing 
hard  gas-retort  carbon,  have  been  attached,  no  effect  is  observed  until  the 
carbons  are  brought  in  contact,  because  the  intensity  of  the  voltaic  current  is 


not  sufficient  to  polarize  the  intervening  air  and  cause  a  disruptive  discharge; 
but,  ouce  brought  in  contact,  a  brilliant  spark  or  intense  light  is  perceptible; 
and  then  the  carbons  may  be  more  or  less  separated  without  interrupting  the 
current ;  and,  with  very  powerful  batteries,  the  distance  between  the  two 
carbons  may  be  increased  to  several  inches. 

By  throwing  a  picture  of  the  charcoal  poles  on  the  disc,  it  is  seen  that  a 
luminous  arc  extends  between  the  two  poles,  and  there  is  a  constant  transfer¬ 
ence  of  heated  particles  going  on  between  the  two  carbons.  It  is  this  passage 


ELECTRICITY. 


366 


of  divided  carbon  which  serves  as  a  conductor  to  the  current,  and  preserves 
its  continuity. 

De  la  Rue  states  that  “  The  length  of  the  luminous  arc  consequently  bears 
a  close  relation  to  the  facility  with  which  the  material  of  the  poles  admits  of 

division 

Scientific  men  have  always  agreed  that  the  transference  of  particles  took 
place  in  the  same  direction  as  the  current,  viz.,  from  the  positive  element  to 
the  negative;  and  the  explanation  is  made  clearer  by  the  discovery  of  Neeff, 
that  the  positive  is  more  strongly  heated  than  the  negative  pole. 

Van  Breda  has  shown  that  incandescent  and  fused  particles  are  not  only 
propelled  from  both  poles  towards  one  another,  but  in  every  direction. 

Maas,  of  Namur,  affirms  that  the  transference  does  not  always  take  place 
from  the  positive  to  the  negative  pole,  but  is  determined  by  the  density  of 
the  charcoal.  He  states  that  he  succeeded  in  reversing  the  direction  of  the 
particles  by  connecting  a  very  hard,  fine-grained  bit  of  carbon  with  the  posi¬ 
tive,  and  a  coarse  soft  piece  of  charcoal  with  the  negative ;  and  he  then  found 
that  the  incandescent  particles  moved  from  the  negative  to  the  positive  pole. 


The  negative  cylinder,  when  examined,  appeared  slightly  excavated ;  the 
positive  one,  slightly  obtuse.  Amidst  this  conflicting  evidence,  the  writer  states 
from  experience  that  the  wasting  of  the  charcoal  points  is  always  unequal,  and, 
provided  they  are  of  the  same  quality,  the  transference  takes  place  regularly 
from  the  positive  towards  the  negative.  By  arranging  a  number  of  crayon- 
holders,  containing  various  metals,  such  as  zinc,  copper,  lead  (Fig.  304), 
according  to  the  method  proposed  by  Mr.  De  la  Rue,  a  number  of  beautiful 
colours  may  be  obtained  by  the  intense  heating  and  partial  combustion  of 
the  metals  copper  throwing  out  a  green  light,  zinc  a  bluish  white,  with  the 
formation  of  a  large  quantity  of  smoke — oxide  of  zinc. 

If  the  charcoal  points  are  brought  together  in  avoid  space,  or  vacuum,  the 
light  is  very  peculiar:  it  appears  softer,  though  still  very  brilliant,  and  pre¬ 
sents  a  marked  difference  to  the  same  light  observed  in  air ;  the  carbons 
appear  to  last  much  longer,  and  the  writer  has  often  thought  that  when  the 
electric  light  is  required  to  be  very  continuous,  as  in  the  Duboscq  lantern,  it 
would  always  be  better,  if  possible,  to  produce  the  light  in  small  glass  chambers 
from  which  the  air  had  been  removed. 

It  has  been  seen  that  the  resistance  of  platinum  wire  to  the  passage  of  the 
electric  current  is  at  least  nine  and  a  half  times  greater  than  that  of  silver. 

When  a  wire  resists  the  passage  of  the  current,  viz.,  motion,  heat  is  the 


CALORIFIC  EFFECTS. 


3^7 


Fig.  305. — Electric  Light  in  vacuo. 


product,  which  may  be  so  increased  by  the  reduction  of  the  thickness  of  the 
metal,  that  it  becomes  intensely  hot. 

A  platinum  wire  of  moderate  thickness  stretched  between  two  upright 
pillars,  of  course  metallic,  becomes  ignited  throughout  its  entire  length,  if 
connected  with  a  battery  of  sufficient  power.  The  writer  has  had  18  feet  of 
wire  incandescent  whilst  using  very  powerful  Grove’s  batteries.  For  experi¬ 
ments  on  the  small  scale,  it  is  well  to  protect  the  platinum  from  the  cooling 
action  of  currents  of  air,  and  by  this  means  a  much  greater  length  of  platinum 


Fig.  306. — Glass  Tube  containing  a  Platinum  Wire, 

Attached  to  one  end  and  connected  with  a  sliding  brass  rod,  which  being  drawn  out  lengthen0  or 

shortens  the  platinum  wire. 


wire  can  be  ignited.  The  light  emitted  is  peculiar,  and  the  wire  appears  four 
or  five  times  thicker  than  it  really  is,  by  irradiation.  In  a  vacuum,  a  wire  of 
platinum  may  be  ignited  which  would  remain  cold  ana  dark  in  the  air.  A 
platinum  wire  which  is  thoroughly  ignited  in  air  remains  perfectly  cool  if  sur¬ 
rounded  with  hydrogen  gas.  This  fact  is  easily  shown  by  using  two  bell-jars  of 
the  same  size,  one  full  of  air  and  the  other  filled,  by  displacement,  with  hydrogen 
from  an  india-rubber  bag.  As  the  jars  are  alternately  placed  over  the  plati¬ 
num  wire,  the  latter  becomes  incandescent  in  the  air.  but  cool  in  the  hydrogen 
(Fig.  307).  This  fact  was  discovered  by  Professor  Grove,  but  is  not  yet  clearly 
!  explained.  Magnus  ascribes  it  to  conduction  ;  and  theoretically  this  idea  seems 
more  consistent  with  the  statement  that  hydrogen  is  really  a  metal.  Tyndall 
'  ascribes  it  to  the  convective  mobility  of  the  gas;  its  particles  are  supposed  to 
be  more  quickly  set  in  motion  than  air,  and  hence  carry  off  more  heat. 

The  dynamical  effect  of  electricity,  and  its  power  of  producing  motion,  is 
well  shown  in  the  movements  of  the  magnetic  needle  belonging  to  the  galva- 


ELECTRICITY. 


368 


nometer,  and  will  be  more  fully  described  in  the  article  upon  Electro- Mag¬ 
netism  ;  and  having  now  discussed  the  various  effects  producible  from  the 
voltaic  current,  viz.,  chemical,  calorific,  magnetic,  and  dynamical,  w?  may 


Fig.  307. 

a,  glass  rod,  insulating  the  top  pole,  b,  from  c,  between  which  the  coil  of  platinum,  p,  is  placed. 


conclude  this  chapter  with  the  description  of  a  few  practical  applications  of 
the  principles  already  described. 

First,  the  use  for  surgical  purposes,  by  Mr.  Sylvan  De  Wilde,  C.E.,  of  the 
Electrical  Probe  and  Forceps. 

Blood,  bone,  and  animal  matter  generally  are  practically  non-conductors 
of  electricity  of  low  tension. 

Soft  iron,  around  which  an  electric  current  is  made  to  circulate,  becomes 
instantly  magnetic.  The  magnetism  ceases  the  instant  the  current  is  broken 
— constituting  what  is  called  an  electro  magnet. 

Advantage  is  taken  of  these  properties  to  detect  the  existence  and  assist  in 
the  extraction  of  bullets  from  wounds. 

The  apparatus  consists  principally  of  four  parts:  1,  the  battery;  2,  the 
alarum  ;  3,  the  probe ;  and  4,  the  forceps,  contained,  with  their  accessories, 
in  a  box  1 1  in.  x  3^  in.  x  2|  in.,  and  is  complete  in  itself,  requiring  no  external 
supplies  for  about  t'  ree  years. 

The  Battery. — Electricity  is  developed  in  a  vulcanite  cell  (on  the  left  of  the 
bell)  by  zinc  and  carbon,  in  a  solution  of  sulphate  of  mercury.  The  pieces  of 
zinc  and  carbon  drop  into  slots  in  the  interior  ends  of  the 'cell,  where  they 
impinge  upon  platinum  springs,  which,  being  riveted  to  conductors  on  the 
exterior  of  the  cell,  form  positive  and  negative  poles. 

The  zinc  and  carbon  are  interchangeable,  it  being  immaterial  as  to  which 
way  the  current  travels  through  the  apparatus. 

The  poles  of  the  battery  come  into  contact  with  the  conductors  of  the 


ELECTRICAL  PROBE  AND  FORCEPS. 


369 


alarum  at  the  top  of  the  partition  on  the  left  of  the  bell,  and  it  is  necessary 
to  see  that  the  metallic  surfaces  are  clean,  as  a  thin  film  of  dirt  or  oxide  will 
prevent  the  passage  of  the  current. 

The  Alarum. — This  consists  of  brass  strips  or  conductors  (mounted  on  an 
insulating  bed  of  vulcanite)  which  proceed  from  the  poles  of  the  battery  to  the 
binding-screws  or  terminals ,  which  stand  on  the  partition  to  the  right  of  the 
bell.  One  of  these  conductors,  on  its  road,  passes  in  the  form  of  silk-covered 
wire  many  times  round  pieces  of  soft  iron,  forming  together  an  electro-magnet. 
It  is  on  the  immediate  right  of  the  bell.  The  instrument  so  far  may  be  tested 
by  making  communication  between  the  two  terminals  or  binding-screws  with 
a  knife-blade  or  any  metallic  conductor.  This  completes  the  circuit :  the 
current  passes,  the  iron  is  magnetised,  the  keeper  (to  which  is  attached  the 
hammer)  attracted,  and  a  stroke  given  on  the  bell.  We  may  thus  know  that 
the  battery  is  in  action,  and  all  metallic  contacts  clean  and  of  sufficient  pres¬ 
sure,  before  attaching  the  wires  of  the  probe  and  forceps  to  the  terminals. 

The  alarum  is  covered  with  glass,  to  keep  out  dirt,  which  is  considered  a 
greater  evil  than  the  partial  muffling  of  the  sound.  Should  a  violent  jerk  affect 
the  adjustment  of  the  hammer  upon  the  bell,  the  glass  can  be  removed  by 
taking  the  screws  out  of  the  beading.  A  piece  of  steel  which  will  serve  this 
put  pose  will  be  found  in  the  receptacle  on  the  left  of  the  battery.  The  bell 
must  be  turned  upon  its  axis  (which  is  excentric)  until  a  position  is  found 
which  gives  a  clear  ring. 

The  Probe  consists  of  two  pointed  steel  wares  firmly  fixed  in  an  ivory  handle, 
and  projecting  about  4  in.  from  it.  These  wires  are  insulated  from  each 
other  by  a  strip  of  vulcanite  lying  between  them.  Between  the  points  and 
the  handle,  the  wires  have  a  slender  vulcanite  tube  passed  over  them,  which 
is  screwed  into  a  short  length  of  German  silver  tube,  upon  which  is  mounted 
a  small  shield.  The  tubes,  thus  screwed  together,  are  free  to  slide  to  and  fro 
about  a  quarter  of  an  inch,  being  pushed  fonvard  by  pressure  of  the  second 
finger  upon  the  shield,  and  thrown  back  by  a  spiral  spring  which  obtains 
purchase  upon  two  screws  inserted  in  the  ivory  handle  through  slots  in  the 
German  silver  tube. 


The  Forceps  consists  of  two  tempered  steel  limbs,  having  curved  and  bow 
handles  like  scissors.  One  of  these  limbs  has  riveted  upon  it  a  slip  of  ivory, 
which,  combined  with  ivory  bushing  of  the  pivot  and  the  small  piece  of  ivory 
between  the  bows,  completely  insulates  it  from  the  other,  in  all  positions. 

To  the  bows  are  screwed  and  soldered  very  pliable  plated  w  ires,  2  ft.  long, 
covered  with  silk,  which  are  coupled  and  soldered  to  similar  w  ires  proceeding 
from  the  two  steel  wires  of  the  probe. 


24 


37° 


ELECTRICITY. 


It  will  be  seen  from  the  above  sketch  that  each  instrument  has  the  electrical 
current  “  laid  on,”  but  broken  at  A  and  B  (the  points  of  the  probe  and  of  the 
forceps).  Let  each  instrument  be  tested  immediately  before  use  by  touching 
and  seizing  a  bullet,  w.iich  will  supply  a  bridge  for  the  current  to  pass  at  A 
and  B,  and  instantly  cause  the  bell  to  ring.  It  is  needless  to  say  that  the 
instruments  cannot  be  used  quite  simultaneously. 

The  box  in  the  right-hand  compartment  contains  about  forty  charges  of  the 
battery,  each  charge  lasting  several  weeks.  Shaking  the  battery-cell  about 
will  often  revive  an  apparently  dead  solution.  It  ends  by  gradually  getting 
too  feeble  to  attract  the  keeper.  It  should  then  be  thrown  away,  the  cell 
washed  out,  and  fresh  charged  when  required. 

Method  of  using. — The  probe  being  handled  as  a  pen,  the  shield  is  pushed 
forward  by  the  second  finger;  this  has  the  effect  of  covering  the  points  of  the 
wires  with  the  vulcanite  tube.  The  instrument  is  now  inserted,  and  the 
wound  explored  until  the  supposed  bullet  is  felt.  The  tube  is  then  allowed 
to  retreat,  by  the  withdrawal  of  the  second  finger,  and  the  substance  is 
examined  with  the  points.  As  it  is  necessary  that  both  points  should  touch 
the  metal  at  once,  it  will  follow  that,  as  the  probings  are  carried  on,  quarter 
and  half  revolutions  of  the  probe  on  its  axis  should  be  made,  by  rolling  it 
between  the  fingers,  as  we  might  otherwise  touch  with  one  point  only,  and 
obtain  no  signal,  as  for  instance  on  the  back  edge  of  a  bullet  at  A. 


Fig.  309. 


If  the  points  become  entangled  in  fibre,  &c.,  they  can  always  be  released 
by  sliding  forward  the  tube  for  a  moment.  The  advantage  of  points  is  their 
ability  to  obtain  good  contact  through  <pus  or  fibre  which  may  overlie  the 
bullet. 

I  he  lodgment  being  ascertained,  the  forceps  are  brought  into  use;  and 
these  equally  give  a  ring  upon  the  bell  when  the  bullet  is  seized,  the  falling 
back  of  the  bell-hammer  showing  if  contact  is  lost.  The  curved  points  will 
seize  the  bullet  in  any  position,  generally  allowing  it  to  revolve  to  that  of 
least  resistance.  As  for  instance,  should  seizure  be  made  at  right  angles  to 
the  bullet,  it  would  revolve  between  the  points,  as  shown  by  the  sketch  at 
G  and  D. 

In  many  cases  the  forceps  could  be  at  once  used,  without  the  intervention 
of  the  probe. 

Should  the  plaited  wires,  by  repeated  twisting,  become  broken,  they  may 


THE  ELECTRIC  TORPEDO. 


37r 


be  resoldered  by  any  tinman  or  the  regimental  smith,  or,  in  emergency,  tied 
on  or  fastened  in  any  way  so  that  fair  metallic  contact  is  made. 

The  probe  was  invented  by  Mr.  De  Wilde  to  solve  the  difficulty  presented 
in  the  case  of  General  Garibaldi.  It  is  made  by  Mr.  Apps,  and  was  submitted 
to  the  Director-General  of  the  Army  Medical  Department  in  December,  1866, 
and,  shortly  after,  approved  in  a  report  by  Professor  Longmore,  of  Netley 
Hospital,  and  by  the  Directors-General  of  the  Navy  and  of  the  Indian  Board. 

The  Electric  Torpedo. 

Among  the  many  important  applications  of  electricity  the  electric  torpedo 
occupies  a  very  prominent  position,  as  a  means  of  defence  against  the  approach 
of  an  enemy  both  by  land  and  by  sea. 

By  sea  this  defence  against  attack  is  carried  out  by  sunken  torpedoes  or 
mines,  containing  charges  of  gun-cotton  or  gunpowder  proportionate  to  the 
depth  of  water,  and  which  are  planted  in  the  harbour  or  channels  to  be  pro¬ 
tected,  in  such  positions  that  the  enemy’s  ships  in  their  approach  must  pass 
over  them,  and,  upon  the  ignition  of  the  torpedo,  be  destroyed  by  its  explosive 
force. 

On  land,  the  torpedo  assumes  the  form  of  a  hidden  mine,  any  number  of 
which  may  be  grouped  around  the  city  or  place  to  be  protected  from  the 
approach  of  the  enemy.  These  mines  are  large  pits  in  the  form  of  inverted 
truncated  cones,  into  the  apex  of  which  the  torpedo  is  placed,  the  rest  being 
filled  with  one  or  two  hundred  tons  of  paving-stones  and  broken  granite,  and 
the  mine  concealed  from  observation;  but,  when  it  is  fired,  il  will  deal  death 
and  destruction  to  all  around. 

The  ignition  of  these  torpedoes  by  land  and  by  sea  is  effected  by  means  of  the 
electric  spark,  and,  by  the  arrangement  of  Mr.  Nathaniel  J.  Holmes,  is  entirely 
under  the  will  and  control  of  the  operator,  and  may  be  employed  with  the 
greatest  safety,  while  at  the  same  time  it  is  certainly  one  of  the  most  deadly 
and  destructive  engines  of  warfare  which  the  mind  of  man  has  devised. 

Of  the  horrors  of  the  torpedo  the  American  struggle  between  North  and 
South  affords  example,  and  the  following  narrative  of  the  blow  ing  up  of  a  large 
five-gun  vessel,  with  a  crew  of  a  hundred  and  twenty  men,  by  means  of  one  cf 
these  torpedoes,  will  suffice. 

The  explosion  took  place  on  a  clear  afternoon,  and  was  w  itnessed  by  many 
persons.  The  boilers,  engines,  and  smoke-stack  went  up  20  or  30  feet,  the 
boilers  bursting  at  the  same  time,  and  the  hull  of  the  vessel  was  reduced  to 
fragments,  while  the  bodies  of  the  crew  were  projected  high  in  the  air,  and  in 
many  cases  their  garments  were,  by  the  force  of  the  explosion,  rgnt  from  their 
bodies,  and  heads,  arms,  and  limbs  were  scattered  in  all  directions.  Not  one 
of  that  crew  came  down  alive.  This  vessel  was  destroyed  in  the  James  River, 
and  stopped  the  advance  of  the  Federal  fleet  for  a  week.  Again,  on  the  15th 
of  December,  1864,  while  in  Mobile  Bay,  the  gun-boat  “Narcissus”  was  blown 
up  by  a  torpedo,  and  crewr  and  vessel  annihilated  in  a  moment.  Admiral 
Farragut’s  ship,  the  “  Richmond,”  which  happened  to  be  within  50  feet  of  the 
torpedo,  was  also  damaged,  and  several  of  the  men  on  board  frightfully  scalded 
and  mutilated.  The  Americans  may  with  justice  remark,  these  torpedoes  are 
infernal  tilings. 

The  torpedo  was  fi'  st  introduced  into  naval  warfare  by  the  Russians  during 
the  advance  of  the  British  fleet  into  the  Baltic,  at  the  time  of  the  Crimean 
war,  in  1854. 


24-2 


3  / 2 


ELECTRICITY. 


These  torpedoes,  constructed  by  Professor  Jacobi,  were  small  iron  tanks, 
filled  with  gunpowder  and  a  charge  of  chlorate  of  potash  and  sugar,  and  fired 
by  percussion,  that  is,  coming  into  contact,  as  they  floated  down  the  stream, 
with  the  hull  of  any  vessel  they  chanced  to  meet.  An  iron  rod,  projecting, 
would  strike  the  ship,  and  by  the  force  of  the  shock  be  driven  back  and  break 
a  vessel  containing  sulphuric  acid  within  the  charge,  and  so  explode  the  mine. 

The  nature  of  the  construction  and  ignition  of  these  torpedoes  rendered 
them  as  likely  to  be  injurious  to  friend  as  well  as  foe,  and  in  time  the  percus¬ 
sion  arrangement  corroded,  and,  when  required  for  service,  they  were  often 
found  useless;  and  no  improved  method  of  construction  being  then  known, 
the  torpedo  was  abandoned  until  the  year  i860,  when  the  Austrian  government 
took  up  the  subject  in  connection  with  the  defence  of  Venice,  by  the  closing  of 
the  harbour  and  three  important  channels  by  electric  torpedoes. 

To  Baron  Ebner  is  due  the  merit  of  these  investigations  into  the  proper 
construction  and  discharge  of  torpedoes  for  naval  defences,  and  he  also  carried 
out  a  series  of  experiments  regarding  the  destructive  effects  of  certain  charges 
of  gun-cotton  and  gunpowder  under  ascertained  conditions,  but  which  were 
interrupted,  after  the  armistice,  after  the  placing  of  five  torpedoes.  In  these 
experiments  nothing  really  practical  was  developed  by  which  the  torpedo  could 
be  introduced  generally  into  naval  and  military  tactics  as  an  auxiliary  to  rifled 
guns  and  ironclads;  and  to  Mr.  N.  J.  Holmes  and  Commander  Maury,  the 
deep-sea  hydrographer,  belong  the  merit  of  reducing  the  whole  practically  into 
a  system. 

In  the  month  of  August,  1863,  during  the  meeting  of  the  British  Association, 
at  Newcastle-on-Tyne,  Mr.  Holmes  carried  out  the  novel  idea  of  firing  an 
1 8 -pounder  cannon  at  Newcastle  each  day  at  1  p.m.,  Greenwich  time;  the 
electric  spark  to  discharge  the  gun  being  flashed  through  the  wire  from  the 
Royal  Observatory,  Calton  Hill,  Edinburgh,  a  distance  of  120  miles.  By 
the  able  assistance  of  Professor  Piazzi  Smythe,  the  Astronomer  Royal  for 
Scotland,  the  necessary  connections  at  the  observatory  with  the  clock 
were  made;  and  each  day  the  clock  transmitted  the  current  to  the  gun 
at  Newcastle,  which  was  discharged  at  1  p.m.,  Greenwich  mean  time, 
to  the  gratification  of  the  Association.  This  time-gun  has  since  been 
permanently  established,  and  is  daily  fired,  enabling  those  at  Newcastle, 
when  they  hear  the  report  of  the  discharge  of  the  gun,  to  set  their  watches 
and  clocks  according  to  correct  Greenwich  time.  The  means  used  for  this 
experiment  were,  first,  the  spark  developed  from  Sir  C.  Wheatstone’s  magneto¬ 
exploder;  and,  secondly,  the  excellent  chemical  fuse  of  Professor  Abel,  of  the 
Royal  Laboratory,  Woolwich,  and  which,  being  inserted  into  the  touch-hole, 
by  its  ignition  fired  the  gun. 

Commander  Maury,  who  witnessed  this  time- gun  experiment,  was  struck 
with  the  importance  of  the  application  for  the  ignition  of  torpedoes  as  a  means 
of  assisting  the  defences  of  the  Confederate  armies  in  the  struggle  then  going 
forward.  Commander  Maury  and  Mr.  Holmes  commenced  a  series  of  experi¬ 
ments,  and  the  result  of  their  labours  may  be  described  as  follows Before 
torpedoes  can  be  safely  relied  upon  for  defence,  the  power  of  ascertaining  if 
they  are  in  perfect  order  is  necessary,  and  that  the  enemy  have  not  destroyed 
the  submarine  connections  between  the  shore  and  the  mine.  This  is  accom¬ 
plished  by  a  peculiar  arrangement  of  parts  within  the  fuse,  charge,  and  mine, 
whereby  the  testing  spark  shall  pass  harmlessly  through  the  mine  without 
exploding  it,  and  telegraphing  through  the  entire  series  of  mines  without  risk 


THE  ELECTRIC  TORPEDO. 


373 


or  danger.  The  importance  of  testing  the  wires  by  sending  an  intensity  cur¬ 
rent  from  Sir  Charles  Wheatstone’s  magneto-electric  telegraph  through  the 
torpedo  is  easily  explained.  According  to  the  old  plan,  a  large  charge  of 
gunpowder  was  placed  under  the  water,  and  the  two  conducting  wires  con¬ 
nected  with  it  brought  to  the  shore ;  and  on  a  vessel  passing  over  it,  directly  the 
terminals  were  attached  to  the  voltaic  battery  the  explosion  took  place.  If  tor¬ 
pedoes  arranged  in  this  simple  way  were  placed  under  the  water,  and  the  enemy 
became  aware  of  their  existence,  they  would  soon  go  to  work  to  destroy  them, 
by  sending  out  at  night,  so  as  to  be  favoured  by  darkness,  small  boats,  with 
men  provided  with  the  proper  tackle,  such  as  ropes  and  grapnels.  On  drag¬ 
ging  the  wires  to  the  surface  of  the  water  and  simply  cutting  them,  not  one 
of  the  torpedoes  could  then  be  fired,  while  those  who  had  charge  of  them 
would  not  be  aware  of  the  circumstance,  and  expect  to  be  able  to  fire  them  at 
any  moment;  on  the  contrary,  the  enemy’s  ships  would  oe  able  to  pass  harm¬ 
lessly  over  the  torpedoes.  Mr.  Holmes  has  made  a  great  improvement,  by 
placing  a  coil  of  fine  platinum  wire  in  the  circuit  near  to  the  fuse,  so  that  the 
intensity  current  from  a  magneto-exploder  or  telegraph  will  not  ignite  the 
charge  when  it  is  allowed  to  pass  through  it.  The  men  having  charge  of  these 
torpedoes  stationed  probably  three  or  four  miles  away,  and  the  wires  being 
connected  with  the  magneto-telegraph,  they  could  easily  send  or  receive  mes¬ 
sages  by  currents  of  electricity  passing  through  the  torpedoes  from  one  instru¬ 
ment  to  the  other,  and  would  thus  afford  satisfactory  evidence  of  all  being  in 
a  proper  condition  to  fire.  On  the  other  hand,  if  they  found  suddenly  the 
telegraph  refused  to  work,  and  it  was  not  in  their  power  to  send  a  message, 
then  they  would  very  likely  say,  “  Depend  upon  it,  our  enemies  have  been  at 
work  and  cut  the  wires.  It  is  useless  to  waste  our  time ;  we  had  better  employ 
some  other  means  of  defence  to  repel  their  ships,  if  they  attempt  to  enter  our 
port.” 


Fig.  310. 

a,  The  Polytechnic  Torpedo,  constructed  by  the  writer;  and,  ft,  Mr.  Holmes's  Torpedo  made  of  iron 

boiler-plate. 


We  will  now  imagine  that  the  wires  have  been  satisfactorily  tested,  and  that 
the  moment  has  arrived  for  igniting  the  torpedoes.  It  may,  however,  be 
naturally  asked,  if  intensity  electricity  will  not  fire  them,  how  can  they  be  ex¬ 
ploded?  We  must  here  recollect,  there  are  two  qualities  of  electricity — intensity 
and  quantity.  The  former  is  used  only  for  testing  the  wires;  the  latter,  quan¬ 
tity  or  accumulated,  is  used  by  Mr.  Holmes  for  igniting  torpedoes  constructed 


374 


ELECTRICITY. 


Fig.  31  i. 

according  to  his  plan.  The  Messrs.  Elliott,  of  Charing  Cross,  have  arranged 
a  very  convenient  and  portable  frictional-plate  electrical  machine,  with  con¬ 
denser  or  small  Leyden  jar  combined,  and,  being  made  of  ebonite,  it  is  always 
in  good  working  order.  The  wires  being  detached  from  the  telegraph  and 
connected  with  this  machine,  which  becomes  charged  by  about  thirty  revolu¬ 
tions,  on  pulling  a  little  trigger  at  the  side,  the  contact  is  made  with  the  torpedo 
and  the  Leyden  jar,  and  the  quantity-spark  is  discharged  in  the  centre  of  the 
fuse,  and  the  explosion  instantly  takes  place. 

1  hese  torpedoes  in  practice  are  usually  arranged  in  groups  of  three,  and 
consist  of  vessels  similar  to  steam-engine  boilers,  made  of  thick  plates  of 
iron  riveted  together,  each  one  being  charged  with  500  lbs.  of  gunpowder, 
i  t  can  easily  be  imagined  that  one  of  these,  placed  16  ft.  under  a  ship  and 
fired,  would  be  quite  sufficient  to  blow  it  into  the  air. 

We  give  a  drawing  of  the  miniature  torpedo  experiment  performed  so  fre¬ 
quently  at  the  Royal  Polytechnic,  Mr.  J.  L.  King,  an  old  and  much-respected 
pupil  of  the  writer,  now  lecturer  at  the  Institution,  superintending  the  arrange¬ 
ments.  A  copper  cylinder  (Fig.  310,  a),  containing  a  few  grains  of  gunpowder, 
and  covered  with  bladder,  is  sunk  in  the  centre  of  the  great  tank,  to  a  depth 
of  about  2  ft.,  and  when  the  spark  is  passed  it  explodes,blowingamodel  ship  high 
into  the  air,  to  the  great  delight  of  all  small  warriors  of  the  rising  generation. 

The  Electric  Lamp. 

The  young  people  who  may  read  this  book  will,  no  doubt,  be  glad  to  hear 
l  rat  they  can  now  experiment  with  the  electric  light  at  a  very  moderate  cost, 
with  a  new  and  beautiful  apparatus  constructed  by  Mr.  John  Browning,  of 
in  Minones.  7  3  *” 


THE  ELECTRIC  LAMP. 


375 


The  apparatus,  Fig.  312,  is  most  simple  and  effective, and,  with  a  small  Grove 
battery  and  a  moderate-sized  lamp,  an  electric  light  may  be  procured  at  about 
the  cost  of  two  or  three  pounds.  There  is  no  clockwork  ;  and  the  regulator  is 
simply  an  electro-magnet  which  cannot  very  easily  be  put  out  of  order.  The 
writer  can  strongly  recommend  this  apparatus  to  those  who  want  a  cheap  and 
good  lamp.  Of  course,  when  an  electric  lamp  is  required  to  be  constantly  used, 
and  is  subjected  to  much  wear  and  tear,  more  substantial  arrangements  are 
required,  as  in  Serrin’s  lamp.  Or,  later  still,  that  of  the  Russian  savan,  Paul 
Pablochkoff,  who  has  perfected  a  new  arrange¬ 
ment  of  the  carbons  by  which  a  larger  and  steadier 
electric  light  is  obtained,  with  little  or  no  mechan¬ 
ism  to  get  out  of  order. 

The  writer  saw  in  the  physical  laboratory  of  Mr. 

Spottiswoode  the  current  of  a  large  coil  excited  by 


Fig.  312. — Mr.  Browning's  new  and 
cheap  Electric  Lamp. 


Fig.  313. — Servin' s  Automatic 
Regulator  of  the  Electric  Light. 


a  powerful  Gramme’s  magneto-electric  machine,  worked  by  a  steam  engine, 
pass  along  the  edge  of  a  thin  piece  of  soft  “  kaolin,”  about  2  in.  in  length,  which 
it  fused,  emitting  all  the  time  a  most  brilliant  light. 

When  carbon  poles  are  substituted  for  the  kaolin,  with  the  direct  agency  of 
the  battery,  the  light  is  dazzling  in  the  extreme. 

In  the  following  description  of  Serrin’s  apparatus,  Figs.  313  and  314  repre¬ 
sent  a  vertical  section  and  plan  (at  the  height  of  the  electro- magnet)  of  appa¬ 
ratus  ;  it  consists — 


376 


ELECTRICITY. 


First,  of  a  motor  or  driving  power  A,  a',  a",  forming  at  the  same  time  the 
motor  and  holder  of  the  positive  electrode,  as  a  motor  ;  it  is  furnished  with  a 
toothed  rack,  and  acts  by  weight  on  the  moving  part  of  the  clockwork.  The 
tube  G,  g',  serves  as  a  guide,  which 
carries  a  binding-screw  stud  E,  which 
serves  to  receive  the  wire  from  the 
positive  pole  of  the  battery. 

Secondly,  of  a  wheel  train,  composed 
of  four  movable  irts,  B  t  H,l,  the  first 
mover  of  a  single  piece  forming  at  the 
same  time  a  toothed  wheel,  K,  and 
pulley,  M.  The  diameter  of  these  last 
are  as  two  to  one,  so  as  to  correspond 
and  be  in  proportion,  as  near  as  miy  be,  to  the  different  consumption  of  the 
positive  and  negative  carbon  points,  and  thus  maintain  the  point  of  light 
stationary.  To  effect  this,  the  wheel  K,  in  turning  under  the  action  of  the 
motor,  A,  a',  a",  allows  the  upper  carbon  point  to  descend,  whilst  the  pulley  M, 
by  the  same  movement,  winds  up  the  chain  N,  o,  P,  and  effecting  at  the  same 
time  the  ascension  of  the  lower  carbon  point.  The  toothed  wheel  K,in  combina¬ 
tion  with  the  other  movable  parts,  serves  to  regulate  the  approach  of  the  carbon 
points  by  the  aid  of  the  flyer  R,  R',  which  carries  the  last  wheel.  This  carries 
besides  a  detent  C,  c',  which  acts  to  prevent  or  permit  the  approach  of  the 
charcoal  points. 

Thirdly,  of  an  electro-magnet,  Q,  wound  round  with  an  isolated  conducting 
wire,  communicating  by  one  of  its  extremities  to  the  binding-stud  S,  and  by 
the  other  to  small  chains  U,  P. 

Fourthly,  the  combination  of  parts,  which  I  will  term  the  oscillating  arrange¬ 
ment,  and  which  forms  the  particular  feature  of  this  improved  regulator. 
a,  b ,  d,  oscillating  support,  properly  so  called,  which  is  held  by  two  arms  of 
equal  length,  a  c,  d /,  jointed,  at  e  f  to  the  plates  or  case  of  the  train ;  the 
joints,  e  /  and  a  d ,  permit  of  a  vertical  to-ancl-fro  movement  of  about  half 
an  inch,  which  movement  is  limited  by  a  stop,  g,  oscillating  between  two 
screws,  h,  l. 

The  pulley  O,  which  is  mounted  on  the  oscillating  support  and  disposed  to 
receive  the  chain  N,  o,  r.  I  call  this  chain  and  pulley  O  the  parts  of  ascension. 
The  pawl  or  catch  7/z,  also  fixed  to  the  oscillating  support,  engages  with  or 
disengages  from  the  teeth  of  the  detent  C,  c',  according  as  it  is  to  be  raised  or 
lowered:  thus,  when  the  stop^  is  in  contact  with  the  screw  /z,  the  gearing  is 
free;  if,  on  the  contrary,  it  separates  itself  a  fraction  of  an  inch,  the  pawl  in 
engages  with  and  stops  the  train,  a,  b ,  n ,  7/,  collars  formed  on  the  oscillating 
support;  they  are  bushed  with  ivory,  so  as  to  isolate  the  lower  carbon-holder, 
and  serve  at  the  same  time  to  guide  the  latter  in  its  raising  movement. 

The  armature  V,  fixed  to  the  oscillating  support,  is  formed  of  a  horizontal 
plate  and  two  vertical  plates  of  soft  iron ;  the  horizontal  part  covers  the 
1  lectro-magnet  Q,  and  the  other  two  are  placed  at  opposite  ends  of  the  soft 
iron  of  the  electro-magnet  but  without  touching  it.  This  armature  is  disposed 
in  such  way  that  its  central  horizontal  line  is  higher  than  the  usual  lines  of 
the  electro-magnet,  thereby  assisting  the  action  of  the  magnet. 

The  appendix  z,  P,  fixed  to  the  base  of  the  carbon-holder  z,  q ,  serves  to  join 
it  with  the  chain  N,  O,  P,  electrically  isolated  at  P. 

The  object  of  the  small  chains  U,  P,  is  for  the  passage  of  the  electric  cur- 


THE  ELECTRIC  LAMP . 


377 


rent,  while  at  the  same  time  they  serve  as  a  variable  counterbalance  by  raising 
the  extremity  P,  and  thereby  compensating  for  the  loss  of  weight  that  the 
lower  carbon  incurs  by  being  used  in  combustion.  The  fixed  support  u  of 
the  chains  is  electrically  isolated.  The  friction  surface  s,  v,  is  also  isolated  at 
v ,  the  helix  v,  r ,  serving  also  to  conduct  a  part  of  the  electric  current  passing 
from  the  lower  carbon  to  the  wire  of  the  bobbin. 

The  suspension  spring  has  for  its  object  to  sustain  the  oscillating  frame 
and  effect  of  the  weight ;  it  can  be  lengthened  or  shortened  at  will  by  the  aid 
of  the  button  p  and  the  pulley  it. 

Action  of  the  Regulator. — The  drawing  represents  the  apparatus  in  action, 
and  the  carbon  points  about  half  used.  The  carbon  points  are  placed  in  their 
supports  a",  q,  while  the  apparatus  has  no  communication  with  a  battery; 
the  electro-magnet  being  inactive,  the  spring  t  should  be  lengthened  in  such 
way  that  the  stop,  g,  presses  lightly  on  the  screw  //,  or  in  this  case  the  detent 
C',  C",  being  in  gear  with  the  hook  in,  is  raised  to  its  highest  elevation.  During 
this  time  the  gearing  is  free,  and  the  charcoal  points  approach  and  come  in 
contact.  By  connecting  the  negative  pole  of  the  pile  or  battery  to  the  bind¬ 
ing  stud,  S,  and  the  positive  pole  to  the  screw  E,  the  electricity  enters  the 
apparatus  by  the  latter,  passes  through  the  motor,  carbon-holder,  and  the 
carbon  itself  by  reason  of  the  contact  which  exists  between  the  two  carbons  ;  it 
will  continue  its  course  by  the  lower  carbon,  the  support  i,q,  the  small  chains 
P,  U,  also  the  friction  surface,  j,  v,  and  helix  v,  r ,  to  the  conductor  wound  on 
the  electro-magnet,  leaving  by  the  binding-screw  stud,  S,  to  re-enter  the  battery, 
and  so  on.  At  the  moment  of  connecting  the  second  pole  of  the  battery,  the 
electro-magnet  becomes  active,  and  the  armature,  V,  is  attracted  and  drawn 
down,  thus  lowering  the  oscillating  frame  or  system ;  the  hook  then  catches 
the  wheel  train.  By  this  action  the  train  is  stopped,  and  the  upper  carbon 
remains  stationary,  while  the  lower  one  being  unable  to  rise,  their  separation 
is  maintained,  and  the  voltaic  arc  formed.  The  arc  being  formed,  the  carbon 
points  are  consumed  by  transfer  and  combustion;  therefore  the  interval 
between  them  increases,  while  the  attractive  force  of  the  bobbin  becomes 
gradually  weaker,  and  the  oscillating  system  raises,  its  motion  being  complete 
when  the  screw-stud,^,  touches  the  screw  //,  the  train  liberated  at  the  same  time 
and  acts  on  the  ascending  parts,  which  thus  effect  the  simultaneous  approach 
of  the  two  carbons;  this  approach  is  effected  in  relation  to  the  unequal  wear 
of  the  carbons  so  as  to  maintain  the  point  of  light  stationary.  After  the 
approach  of  the  carbons  the  electricity  passes  more  easily,  causing  the  arma¬ 
ture  to  be  attracted  more  strongly,  and  to  overcome  the  resistance  of  the 
suspending  spring  so  as  to  draw  dowm  the  oscillating  frame,  when  the  hook 
gears  with  the  train  and  prevents  the  carbons  approaching  until  the  wear 
again  produces  another  approach,  followed  by  another  stop,  and  so  on.  'I  hus, 
by  the  alternate  opening  and  closing  of  the  circuit,  the  movements  described 
can  be  reproduced  and  continued  at  pleasure,  and  so  forming  and  determin¬ 
ing  the  voltaic  arc  by  its  self-action.  After  the  preceding,  it  will  be  seen  that 
it  is  the  oscillating  system  or  frame  which  determines  all  the  actions  of  the 
regulator,  and  separation  and  adjustment  of  the  carbons.  The  seven  principal 
pieces  of  which  it  is  composed  produce  the  different  effects  under  the  action 
of  electro-magnetic  apparatus  in  communication  with  the  voltaic  arc. 

The  recapitulation  of  the  seven  principal  parts  which  compose  the  oscilla¬ 
ting  system  or  frame  are  the  following: — First,  the  suspension  spring  t; 
secondly,  the  stop^y  thirdly,  the  electro-magnet  Q  and  v ;  fourthly,  the  carbon- 


378 


ELECTRICITY. 


Fig.  315. — Illumination  of  the  Ball  and  Cross  and  Dome  of  St.  Pauls 

by  the  Electric  Light. 

holder  i,  q;  fifthly,  the  ascending  part  O  and  N,  O,  P;  sixthly,  the  hook  of 
detent  7 n;  seventhly,  the  compensating  chain  U,  P. 

With  a  number  of  Serrin's  lamps,  Captain  Bolton  and  the  writer  illumi¬ 
nated  Trafalgar  Square  and  St.  Paul’s  Cathedral,  on  the  occasion  of  the 
festivities  connected  with  the  nuptials  of  H.R.H.  the  Prince  of  Wales. 
The  night  was  untortunately  too  foggy  to  enable  even  the  strongest  lights  to 
pierce  the  smoke-contaminated  atmosphere  of  London,  so  that  the  imagination 
(unless,  like  the  writer,  the  spectator  was  close  to  the  soot-begrimed  dome  of 
St.  Paul’s)  had  to  suppose  what  might  have  been  the  effect  if  the  air  had  been 
free  from  the  pea-soup  mixture  of  aqueous  vapour  and  smoke. 


Fig.  316. —  llic  Shepherd  discovering  the  Magnetic  Stone  on  A  fount  Ida 

with  the  Iron  of  his  Crook. 

MAGNETISM. 

The  magnetic  or  b'ack  oxide  of  iron,  Fe304,  sometimes  called  the  lead- 
stone  or  loadstone,  is  estimated  as  one  of  the  most  valuable  ores  of  iron, 
because  it  enjoys  the  property,  when  freely  suspended,  of  pointing  to  the 
north  ;  and  it  does  this  by  virtue  of  an  inherent  property  which  belongs  to  it, 
called  magnetism. 

The  loadstone  occurs  native,  and  crystallizes  in  cubes,  and  is  said  to  have 
been  discovered  by  a  shepherd  on  Mount  Ida,  who  first  noticed  that  the  iron 
of  his  crook  was  attracted  by  it.  (Fig.  316.)  It  was  called  in  England  the 
/" destone ,  or  “  leading  stone,”  from  the  Saxon  laden ,  “  to  lead,”  and  so  termed 
because  it  caused  iron  to  follow  it.  It  was  called  the  love-stone,  perhaps  after 
the  French  had  suggested  the  sentimental  nameol  l' aim  ant,  “  the  affectionate, ” 
because  it  had  a  strong  affection  for  iron,  and  draws  that  metal  unresistingly 
to  ii  self. 

The  magnet  was  not  only  called  in  agues.  but  “lapis  Ileraclcus,”  from 
Meraclea,  a  city  of  Magnesia,  a  part  of  ancient  Lydia,  in  Greece.  It  is  also 
called  tapis  nauticus, because  of  its  use  in  navigation  ;  and  siderites,  because 
the  mineral  attracts  iron,  which  the  Greeks  called  vcdepos. 

“The  earliest  mention  in  English  records  of  the  primitive  mariner’s  com¬ 
pass  is  that  by  Alexander  Neckham,  who  describes  the  same  in  his  ‘  Treatise 
on  Things  pertaining  to  Ships.’  Neckham  was  born  at  St.  Albans  in  1 1 57- 
A  translation  of  his  works,  from  the  Latin,  was  published  in  1866.  In  the 

379 


38° 


MAGNETISM. 


reign  of  Edward  HE,  the  magnet  was  known  by  the  name  of  the  sail-stone 
or  adamant ,  and  the  compass  was  called  the  sailing-needle  or  dial,  though  it 
is  long  after  this  period  before  we  find  the  word  compass.  A  ship  called  the 

‘  Plenty,’  sailed  from  Hull  in  1338 ;  and  we  find  that 
she  was  steered  by  the  sailing-stone.  In  1345, 
another  entry  occurs  of  one  of  the  king’s  ships, 
called  the  ‘  George,’  bringing  over  sixteen  horologies 
from  Sluys,  in  Normandy,  and  that  money  had  been 
paid  at  the  same  place  for  twelve  stones,  called 
adamants  or  sail-stones,  for  repairing  divers  instru¬ 
ments  pertaining  to  a  ship.” 

Fine  large  pieces  of  loadstone  are  usually  mounted 
in  handsome  brass  or  silver  boxes,  and  were  highly 
prized  in  the  reign  of  King  Charles  IE,  when  the 
Royal  Society  of  England  began  to  exert  itself  in 
the  acquisition  of  scientific  knowledge. 

When  examined  with  a  magnetic  needle,  the 
mineral  is  found  to  have  two  points  where  the  mag¬ 
netic  virtue  exists  in  the  greatest  intensity:  these  are 
called  poles,  and  are  connected  with  the  pieces  of  soft  iron  which  protrude 
from  the  case  containing  the  loadstone  ;  they  take  off  the  friction  and  wear 
and  tear  of  the  mineral,  whilst  all  cutting  of  the  stone,  in  order  to  obtain  a 
hollow  space  between  the  two  poles,  as  in  an  ordinary  horse-shoe  magnet,  is 
avoided.  The  magnetism  from  the  loadstone  is  easily  conferred  upon  and 
retained  by  hardened  steel. 


Fig.  317. 

A  mounted  Loadstone. 


Fig.  31 8. —  Two  Bars  of  Steel, 

Each  marked  N  and  s  at  their  opposite  extremities,  and  connected  by  pieces  of  soft  iron,  called  “feeders.” 

It  is  only  necessary  to  rub  the  steel  or  drag  the  loadstone  round  in  one 
direction,  taking  care  to  put  the  pole  N  of  the  latter  on  the  end  of  the  steel 
bar  marked  s.  An  assemblage  of  steel  plates  in  the  form  of  an 
elongated  horse-shoe,  when  carefully  magnetised  and  fixed  to¬ 
gether,  constitutes  a  kind  of  magnetic  battery  having  great  y 
increased  powers  (Fig.  319.) 

This  would  be  called  a  compound  horse-shoe  magazine 
or  battery,  composed  of  an  odd  number  of  horse-shoe  bars  of 
different  lengths.  The  union  of  unequal  bars  produces  a  step¬ 
like  arrangement  at  the  poles,  the  largest  bar  being  in  the 
centre,  with  the  pair  of  bars  next  largest  on  each  side,  and  so 
on  progressively.  This  peculiar  arrangement,  with  all  other 
magnetic  instruments,  may  be  obtained  from  Elliott,  Charing 
Cross,  and  possesses  several  advantages,  especially  when  used 
to  confer  magnetism  on  other  pieces  of  steel. 

A  most  instructive  experiment— and,  indeed,  one  that  shows 
„  __  the  nature  of  all  magnets  (which  may  be  regarded  as  made  up 

riG.  319.  Gf  an  infinite  number  of  small  polarized  particles) — is  con¬ 
structed  by  placing  iron  filings  in  a  glass  tube,  and  then  magne¬ 
tizing  them  by  placing  the  glass  tube  on  the  poles  of  an  electro-magnet,  or 


THE  MAGNETIC  NEEDLE. 


38« 


passing  it  in  the  usual  way  over  the  poles  of  a  steel  permanent  magnet.  The 
iron  filings  now  show  polarity,  one  end  of  the  glass  tube  containing  them 
being  north,  the  other  south  ;  but  directly  the  tube  is  well  shaken,  all  the 
polarity  of  the  particles  of  iron  is  destroyed  by  the  reversal  of  the  poles  and 
confusion  of  the  order  of  the  polarity  of  each  separate  iron  tiling  or  particle, 
iron  is  only  temporarily,  but  steel  is  permanently,  magnetized  by  contact 
with  the  permanent  magnet  or  electro-magnet. 

The  magnets  (Fig.  320)  bearing  the  name  of  Scoresby  are  composed  of 
many  magnetized,  laminated  steel  plates,  combined  together  so  as  to  act 


Fig.  320. — Scoresby' s  Magnets. 


Fig.  321. 


uniformly  as  one  bar.  by  which  means  a  powerful  magnetic  arrangement  is 
obtained.  A  piece  of  steel,  usually  called  a  need'e,  when  carefully  balanced 
and  suspended  on  a  sharp  point  with  a  central  hard  metal  cap,  and  then 
magnetized,  is  called  a  magnetic  steel  needle. 

It  is  extremely  useful  for  showing  the  influence  of  the  magnetism  of  the 
earth  as  regards  the  horizontal  directive  force,  and  is  absolutely  necessary  in 
showing  a  repetition  of  the  facts  already  explained  in  the  article  on  “  Static 
Electricity”  (page  240),  viz,  that  just  as  similar  electricities  repel,  and  oppo¬ 
site  ones  attract,  so  a  north  pole  of  a  magnet  repels  the  north  pole  of  the 
magnetic  needle,  and  the  south  behaves  in  a  like  manner  with  the  south  pole 
of  the  needle.  Dissimilar  magnetisms 
attract,  therefore,  the  north  pole  of  a 
bar  magnet  ;  one  of  those,  shown  at 
Fig.  318,  will  attract  the  south  pole  of 
the  needle,  and  vice  versa. 

At  Elliott's  maybe  obtained  magne¬ 
tic  needles  suspended  in  a  beautiful 
manner,  so  that  the  needle  moves  either 
in  a  horizontal  or  in  a  vertical  plane. 

When  the  needle  moves  in  the  horizon¬ 
tal  plane,  it  is  an  ordinary  mariner’s 
compass  ;  but  when  it  is  free  to  move 
in  a  perpendicular  plane,  it— however 
carefully  balanced  before  magnetizing 
—  dips  downwards,  and  points  to  the 
earth  like  a  finger-post,  directing  the 
eyes  of  the  student  to  the  terrestrial 
power  of  magnetism  which  causes  the 
‘dip-” 

The  direction  of  the  horizontal  magnetized  needle  not  only  varies  daily, 
“ailed  “  diurnal  variations,”  but  it  has  changed  during  various  periods  of  years. 
The  magnetic  needle  does  not  point  due  north  and  south,  but  in  a  plane  or 


FlG.  322. — Needle  suspended ,  and 
dipping  towards  the  Earth. 


382 


MA  GNE  T/SM. 


direction  peculiar  to  itself,  called  the  magnetic  meridian,  to  distinguish  it  from 
the  true  or  terrestrial  meridian.  Magnetic  meridian  lines  are  planes  passing 
through  the  centre  of  the  earth  in  the  direction  of  the  magnetic  needle.  The 
terrestrial  meridian  is  the  plane  passing  through  the  same  place  on  the  axis  of 
the  earth. 

The  angle  made  by  these  two  planes  is  called  the  declination  of  the  needle. 
It  is  determined  by  measuring  the  angle  which  the  direction  of  the  needle 
makes  with  the  meridian  line.  The  declination  was  eastward  at  the  begin¬ 
ning  of  the  17th  century;  it  was  zero,  or  o,  in  1660, i.e.,  the  needle  pointed  due 
north  and  south.  The  declination  now  changed  to  the  westward,  and  had 
increased  to  24°  30'  in  the  year  1818,  since  which  period  it  has  steadily  retro¬ 
graded,  and  about  ten  years  ago  had  reached  210  48'  in  London. 

It  would  appear  from  the  observations  set  on  foot  many  years  ago  by 
General  Sabine,  that  the  sun  and  moon  are  magnetic,  and  do  affect  the  needle 
in  its  diurnal  movements. 


The  marine  compass  only  differs,  from  the  ordinary  one  in  being  suspended 
in  such  a  manner  that  the  motion  of  the  vessel  shall  not  disturb  its  horizontal 
position.  The  marine  azimuth  compass  (Fig.  323)  is  a  more  elaborate  mari¬ 
ner’s  compass,  having  within  the  circumference  of  the  inner  box  sights  for 
determining  the  angular  distances  of  objects  from  the  magnetic  meridian, 
and  being  hung  in  detached  gimbals. 

The  dipping  needle  or  inclination  compass  is  also  found  to  vary  as  the  dip 
increases,  as  might  be  expected,  the  nearer  we  approach  to  the  north  pole.  At 
a  point  in  jo°  5'  of  north  latitude  and  96°  46'  west  longitude  on  the  west 
coast  of  Boothia  Felix,  a  place  was  discovered  by  Captain  Parry  (the  north 
magnetic  pole)  where  the  dipping  needle  became  vertical,  and  the  horizontal 
compass  ceased  to  move  right  or  left,  or  traverse.  Captain  James  Ross  dis¬ 
covered  the  other  end  of  the  great  terrestrial  magnetic  power,  the  south 
magnetic  pole,  to  be  about  latitude  7 30  south  and  longitude  130°  east. 

Hie  student  may  realise  such  movements  of  the  dipping  needle  by  laying 
one  of  the  bar  magnets  (Fig.  318)  in  the  centre  of  a  sheet  of  cardboard  on 
which  a  circle  has  been  described. 

On  moving  the  dipping  needle  round  the  circle,  it  will  be  found  to  take  the 
vertical  position  at  the  poles  A  A,  whilst  it  becomes  horizontal  at  the  equatorial 
position  b  b,  i.e.  midway  between  the  north  and  south  pole. 

The  inclination  or  dip  varies  like  the  horizontal  declination.  At  London,  it 
was  70°  27'  in  1720,  69°  2'  in  1833,  and  68’  51'  in  1849;  at  the  present  time  it 
is  about  68°  30'. 


2ND  UC ED  M A  GNE  TISM. 


383 


The  earth  being  virtually  an  enormous  magnet,  whose  north  pole  is  in  the 
southern  hemisphere,  and  vice  versa ,  must  affect  all  ferruginous  matter  on 
the  earth  by  induction. 


Ni 

,'w  ^ 

- 

,, 

fc,  - '  I 

1 

P 

==|k 

mm 

IE?jW 

5lgf 

It  was  stated,  in  the  article  on  Electricity,  that  the  term  induction  wcu'd 
have  to  be  used  again;  and  the  student  is  reminded  that  this  is  defined  to  be 
|  the  magnetic  influence  set  up  by  the  mere  neighbourhood  or  proximity  of  a 
body — the  earth,  or  the  loadstone,  or  a  magnetized  steel  bar — having  or 
■  possessing  the  magnetic  virtue  or  force. 

By  placing  variously  shaped  pieces  of  soft  iron  near  a  powerful  magnet, 
they  are  supported  or  attracted  so  long  as  the  magnet  is  kept  sufficiently  near 
them ;  but,  as  the  distance  is  increased,  they  drop  off  one  by  one. 


F 10.  325. —  Variously  shaped  pieces  of  soft  Iron  for  showing  Induced 

Magnetism. 

The  magnetic  power  so  quickly  conferred  on  soft  iron  is  as  rapidly  lost 
when  it  is  removed  from  the  disturbing  cause,  reminding  one  of  conductors 
of  electricity,  which  cannot  maintain  polarity;  whereas  steel,  which  acquires 
magnetic  power  more  slowly,  retains  it  with  a  tighter  grasp,  and,  like  non¬ 
conductors  of  electricity,  glass,  wax,  &c.,  can  maintain  magnetic  polarity. 


384 


MAGNETISM. 


Fig.  326.  —  Model  made  by  Elliott, 

Showing  that  electrical  currents  circulating  around  a  globe 
produce  mangetic  currents. 


On  the  supposition  that  all  terrestrial  magnetism  has  an  electrical  origin, 
and  is  produced  by  currents  of  electric  force  which  circulate  around  the 
globe,  a  very  pretty  piece  of  apparatus  is  constructed,  consisting  of  a  d  stri- 
bution  of  wires,  covered  with  silk,  over  a  terrestrial  globe  in  parallel  lines  of 

latitude. 

The  dipping  needle  and 
horizontal  needle  held  in  dif¬ 
ferent  positions  on  the  surface 
of  the  globe,  whilst  the  wires 
are  connected  with  the  voltaic 
battery,  give  the  student  a 
very  good  notion  of  the  natural 
directive  power  of  the  mag¬ 
netism  that  exists  over  the 
surface  of  the  earth  on  which 
we  live,  and  also  illustrates 
again  the  “  inductive ”  power 
of  magnetic  force. 

In  the  year  1600,  277  years 
ago,  Dr.  William  Gilbert,  the 
physician  to  Queen  Elizabeth, 
published  a  work  entitled  “  De 
Magnete,”  or  “  On  the  Magnet,”  and  in  that  book  are  these  words  :  “  Magnus 
magnes  ipse  est  globus  terrestris,”  “  The  earth  itself  is  a  great  magnet.” 

The  force  which  rules  the  position  of  the  magnetic  needle  is  neither  attrac¬ 
tive  nor  repulsive,  but  simply  directive.  A  magnetic  needle  floating  on  a  cork 
neither  advances  nor  moves  backward  ;  it  simply  takes  a  position  nearly  north 
and  south,  and  places  itself  in  the  magnetic  meridian. 

The  engraving,  Fig.  328,  is  a  correct  copy  of  the  photographic  curves  of 
the  self-registering  “  Declination  Magnetograph,”  as  used  at  the  Magnetic 
Observatory  at  Stonyhurst  College,  near  Blackburn. 

This  is  one  of  a  series  of  magnetic  instruments  which  are  self-registering 
night  and  day;  and  it  is  interesting  to  notice  in  the  photographic  curves  the 
amount  of  disturbance  shown  between  the  8th  and  10th  of  August,  1868.  The 
instruments  are  under  the  charge  of  the  Rev.  S.  G.  Perry,  who  has  most  kindly 
furnished  the  following  drawing  and  description  of  the  Magnetic  Observatory 
at  Stonyhurst : 

“An  idea  of  the  disposition  of  the  instruments  may  be  formed  from  the 
drawing  (Fig.  327),  and  a  very  brief  description  will  make  it  still  more  clear. 

‘‘The  instruments  record  the  oscillations  of  three  magnets  suspended  under 
the  glass  shades  ;  and  we  thus  get  completely  all  the  changes,  both  as  to  direc¬ 
tion  and  intensity,  in  the  earth's  magnetism.  The  magnet  which  is  to  the 
right  in  the  sketch  is  suspended  by  a  silk  thread  in  the  magnetic  meridian, 
and,  by  the  aid  of  a  mirror  attached  to  it,  describes  on  a  cGinder,  which  is 
put  in  motion  by  the  clock  on  the  centre  pier,  all  the  variations  in  the  magnetic 
declination.  The  other  two  magnets  give  the  two  components  of  the  total 
magnetic  force  of  the  earth.  That  which  records  the  variations  of  the  vertical- 
component  rests,  under  the  shade  near  the  doorway,  on  two  agate  edges  ; 
whilst  the  horizontal  component  magnet  is  suspended  by  a  double  steel  thread, 
under  the  shade  to  the  left  of  the  picture,  and  is  held  nearly  at  right  angles 
to  the  magnetic  meridian  by  the  torsion  of  the  thread. 


A  MAGNETIC  OBSERVATORY. 


385 


Fig.  327. —  The  Magnetic  Obseivatory  at  Stony  hurst  College. 

“  Under  the  clock-box,  which  stands  in  the  centre,  are  the  three  cylinders 
covered  with  sensitive  paper.  To  each  magnet  is  attached  a  semicircular 
mirror,  which  sends  the  rays  from  a  jet  of  gas  to  one  of  the  cylinders  in  the 
clock-box,  and  thus  describes,  by  a  curved  line,  all  the  oscillations  of  the 
magnet.  A  second  semicircular  mirror  is  fastened  to  the  pier  on  which  the 
instrument  stands,  and,  describing  always  a  straight  line  on  the  cylinder 
which  is  opposite  to  it,  gives  the  zero  line  for  the  curve. 

“These  magnetographs  were  constructed  by  Mr.  Adie.  and  are  similar  in 
nearly  every  respect  to  those  made  for  the  Kew  Observatory,  under  the  direc¬ 
tion  of  Mr.  Welch. 

“  The  magnetic  room  is  built  underground  to  prevent  sudden  changes  of 
temperature,  and  we  have  been  so  fortunate  that  the  daily  range  is  scarcely 
over  o  20.” 

It  has  been  well  said,  “  that  accidents  may  arise  in  the  best  regulated 
families ;  ”  and  so  it  happened  on  one  occasion  at  the  Stonyhurst  Observatory, 


386 


MAGNETISM. 


when  the  self-registering  or  automatic 
magnetograph  indicated  a  violent 
“  magnetic  storm  ”  at  a  particular  hour 
and  date.  On  inquiring  by  telegraph 
at  other  important  magnetic  observa¬ 
tories  on  the  Continent  and  elsewhere, 
it  was  found  that  in  England  and 
distant  parts  of  the  world  they  had 
experienced  only  the  usual  magnetic 
disturbances  or  oscillations.  The  ap¬ 
parent  contradiction  was,  however,  ex¬ 
plained  by  the  discovery  that  the  pains¬ 
taking  gardener  had  rolled  his  largest 
iron  roller  over  a  little  grass-plat  which 
was  laid  down  close  to  a  half  window 
lighting  the  staircase  leading  to  the 
subterranean  observatory.  By  remov¬ 
ing  the  turf,  accidental  “  magnetic 
storms  ”  not  in  nature’s  grand  pro¬ 
gramme  were  hereafter  prevented. 

It  is  curious  that  e\eiy  kind  of  vibra¬ 
tion  assists  the  magnetization  of  iron 
or  steel  by  terrestr.al  magnetism.  If 
half-a-dozen  iron  wires,  12  or  15  in.  in 
length,  are  twisted  strongly  together 
whi. st  held  in  the  direction  of  a  dip- 
p.ng  needle,  viz.  68°,  they  become  very 
magnetic,  and,  having  now  distinct 
poles,  will  affect  a  magnetic  needle  like 
a  steel  bar  magnet.  Iron  columns, 
guns,  the  plating  of  ships  of  war,  car¬ 
goes  of  iron  or  steel,  all  acquire  mag¬ 
netic  pow  er  ;  and,  until  this  fact  wras 
understood  and  provided  for,  many 
disastrous  shipwrecks  were  caused  by 
the  compass  pointing  in  the  wrong  di¬ 
rection,  and  thus  conducting  the  un¬ 
fortunate  ship  to  the  rocks,  instead  of 
keeping  her  in  mid-ocean.  Mr.  Barlow 
has  devised  certain  means  by  which  the 
compasses  of  ships  may  be  corrected, 
and  the  influence  of  local  magnetic 
attraction,  due  to  the  guns,  or  shot,  or 
other  iron  or  steel  cargo,  neutralized,  so 
that  the  ‘‘  directive ”  force  of  terrestrial 
magnetism  alone  shall  guide  the  ship 
over  the  pathless  ocean.  A  late  and 
lamented  friend  of  the  writer  (Mr. 
Evan  Hopkins)  tried  a  vast  number 
of  experiments,  and  wrote  an  interest¬ 
ing  pamphlet  on  terrestrial  magnetism, 


Fig.  328. 


HOPKINS'S  EXPERIMENTS. 


3**7 


with  reference  to  the  compasses  of  iron  ships,  their  deviation  and  remedies. 
It  is  impossible  in  our  limits  to  do  justice  to  the  arguments  brought  forward 
and  discussed  by  Mr.  Hopkins  ;  but  the  remarks  made  at  the  termination  of 
the  debate  at  the  Royal  United  Service  Institution  on  his  paper  will  give  the 
reader  some  notion  of  the  opinions  entertained  by  the  meeting  on  the  method 
of  destroying  the  polarity  of  iron  ships,  as  proposed  by  Mr.  Hopkins. 

“Sir  FREDERICK  Nicholson:  The  subject  has  been  treated  in  an  eminently 
practical  way.  In  the  abstract  of  Mr.  Hopkins’s  papers,  I  find  that  there 
is  one  statement  which  appears  tome  the  most  important,  that  is,  Mr.  Hopkins 
says  he  is  prepared  to  destroy  the  polarity  of  any  given  ship  in  ten  minutes. 
The  only  question  I  wish  to  ask,  because  the  gist  of  the  paper  lies  in  that 
assertion,  is  whether  Mr.  Hopkins  has  performed  that  operation  upon  any  ship. 

“  Mr.  Hopkins  :  No,  not  in  any  ship  as  yet ;  but  I  have  made  experiments 
on  long  bars  and  plates  of  iron,  and  I  am  quite  satisfied  that  I  can  produce 
the  same  results  on  the  iron  plates  of  a  ship.  In  reply  to  the  observations 
which  have  been  made  I  will  not  detain  you  long,  because  I  do  not  think  the 
remarks  made  require  lengthy  replies.  First,  with  regard  to  Sir  Edward 
belcher’s  remarks,  he  said  that  I  stated  that  there  was  no  magnetic  pole.  I 
did  not  state  that  there  was  no  magnetic  pole  ;  on  the  contrary,  I  have  endea¬ 
voured  to  explain  that  the  entire  areas  bonneted  by  the  antarctic  and  the  arctic 
circles  are  the  great  magnetic  poles  of  the  earth ,  towards  which  all  the  magnetic 
meridians  converge.  I  do  not  mean  to  say  for  one  moment  but  that  a  dipping 
needle  at  the  north  latitude  of  70°  approached  nearly  90°,  observed  by  Sir 
James  Ross,  and  probably  over  a  great  number  of  square  miles  in  that  region  ; 
but  I  have  seen  dipping  needles  approaching  90°  near  the  equator.  There  are 
many  places  in  the  islands  of  Scotland,  also  in  Norway,  Sweden,  and  Russia, 
where  the  dipping  needle  will  not  only  approach  90°,  but  remain  at  90°.  There¬ 
fore  I  repeat  that  the  dip  of  the  dipping  needle  does  not  necessarily  depend 
on  the  action  of  the  terrestrial  pole,  but  on  local  attraction.  Besides,  neither 
experiments,  analogy,  nor  observations  on  the  magnetic  meridians  support  the 
notion  of  the  magnetic  pole  being  merely  a  mathematical  point  near  Boothia 
Gulf.  We  have  only  to  prolong  the  observed  magnetic  meridians  to  the  circle 
of  7o°of  latitude  to  show  the  fallacy  of  the  Boothian  pole.  We  must  be  guided 
by  the  meridians  of  the  needles  to  determine  the  position  of  the  active  polar 
areas.  Go  to  Norway ;  go  to  Sweden  ;  where  do  the  needles  point?  Do  they 
point  to  Boothia  Felix?  No;  they  do  not.  They  point  towards  the  arctic 
region,  and  not  to  any  special  point.  With  regard  to  the  other  point  that  Sir 
Edward  stated  with  reference  to  the  compass,  I  do  not  believe  there  is  a  pos¬ 
sibility  for  the  compass  to  point  correctly  unless  it  be  left  entirely  under  the 
control  of  the  great  terrestrial  force:  any  interference,  whether  by  magnets  or 
electric  appliances,  can  only  increase  the  confusion  and  danger,  and  therefore 
the  compass  should  not  be  tampered  with,  but  left  to  act  freely  and  under  the 
sole  influence  of  terrestrial  magnetism.  With  regard  to  what  Captain  Selwvn 
stated  about  the  steering  compass.  He  said,4  Never  mind  that ;  I  believe  you 
do  not  care  much  for  the  steering  compass ;  you  go  by  the  standard  compass.’ 
Well,  there  is  now  always  a  difference  between  the  standard  and  the  steering 
compasses.  We  know  that  in  iron  ships  that  difference  constantly  varies.  You 
do  not  know  what  the  variation  is  that  is  constantly  going  on.  Were  you 
certain  of  the  exac  t  amount  of  variation,  it  would  be  like  the  watch  and  chro¬ 
nometer  spoken  of  by  Captain  Selwyn  ;  but  vou  cannot  compare  the  case  of 
your  watch  and  chronometer  with  those  of  the  standard  and  steering  com- 

25  —2 


388 


MAGNETISM. 


passes  when  you  have  an  iron  vessel,  and  where  you  have  a  perpetual  change 
going  on  in  the  action  of  the  polarity  of  the  iron  vessel.  With  regard  to  the 
reflector,  I  see  Captain  Selwyn  apprehends  difficulty.  I  see  none,  and  the 
appliance  is  already  appreciated  by  several  experienced  captains.  I  do  not 
think  there  would  be  much  difficulty  in  seeing  a  compass,  with  a  good  strong 
light,  with  a  12-inch  card  at  a  distance  of  even  30  feet.  However,  I  leave  that 
to  others.  There  is  one  thing  Sir  Edward  Belcher  mentioned  with  regard  to 
the  needles.  I  am  perfectly  familiar  with  all  the  needles  they  use  in  high 
latitudes.  They  are  utterly  worthless  in  directive  power.  As  to  the  dipping 
needles,  they  have  no  directive  power  whatever,  and,  as  justly  observed  by 
Captain  Fishbourne,  have  no  lateral  directive  power  at  all,  and  cannot  there¬ 
fore  serve  as  guides  to  determine  questions  connected  with  meridian  lines. 
The  curved  magnetic  needle  will  act  where  neither  the  straight  nor  the  dipping 
needles  can  be  rendered  serviceable  in  high  latitudes.  It  only  remains  for 
me,  in  conclusion,  to  thank  you  for  the  patience  and  kindness  with  which  you 
have  listened  to  the  observations  I  have  made. 

“The  Chairman:  I  am  sure  there  will  be  but  one  opinion  among  you  as  to 
a  vote  of  thanks  to  Mr.  Hopkins  for  the  very  interesting  paper  he  has  read.  He 
has  brought  forward  some  of  the  old  ideas  relating  to  magnetism,  which  many 
here  were  not  acquainted  with,  and  he  has  given  us  some  new  ideas.  I  must 
say  that  his  idea  with  respect  to  the  bent  needle  is  one  which  I  think  is  deserv¬ 
ing  of  a  trial.  I  must  also  say  1  should  like  to  see  that  dissipation  of  the  polarity 
of  a  ship  tried,  although  I  am  afraid  that  the  soft  iron  of  the  ship  would  become 
magnetized  by  some  other  extraneous  cause  at  present  unknown.  I  really 
believe  this,  although  we  are  very  thankful  to  him  for  what  he  has  told  us,  that 
we  shall  still  find  it  positively  necessary  to  have  recourse  to  observation.  I 
hope  what  you  have  heard  to-night  will  strengthen  your  confidence  in  the 
compass  as  a  means  of  steering.  There  is  another  remark  about  the  pole.  As 
I  have  passed  within  70  miles  of  it,  and  the  dip  was  89°  47",  I  must  say  that 
I  can  only  look  upon  the  pole  as  capable  of  being  defined,  not  perhaps  exactly 
as  a  pffint,  but  very  nearly  as  a  point,  because  as  I  passed  up,  I  changed  from 
89°  47"  north  dip  to  89°  46"  south  dip.  With  'respect  to  the  deviation  of  the 
compass,  it  has  been  an  old  thing  with  us  who  have  been  in  high  latitudes. 
We  know  perfectly  well  that  we  suffer  the  same  inconvenience  which  is  ex¬ 
perienced  now  in  iron  ships.  In  Behring’s  Straits,  in  going  about  there,  the 
deviation  of  the  ship  amounted  to  six  points  of  the  compass  ;  and  I  can  say, 
which  I  have  no  doubt  Captain  Maguire  will  corroborate  me  in.  that  we  should 
have  had  the  greatest  difficulty  in  the  world  to  take  our  ships  up  into  the 
position  we  did,  if  it  was  not  for  the  admirable  charts  of  Admiral  Bechey.  and 
in  which  expedition  Sir  Edward  Belcher  served.  There  is  onlvcne  other  point. 

I  will  say  that  I  have  listened  to  this  paper  with  a  great  deal  of  gratification 
and  pleasure,  because,  during  the  course  of  my  service  in  the  Arctic  regions,  it 
so  happened  that  for  two  years  I  was  not  able  to  use  a  compass  at  all ;  there¬ 
fore  I  am  able  to  appreciate  anything  that  will  increase  the  value  of  it.” 

The  sequel  is  soon  told,  for  Mr.  Hopkins  caught  a  violent  cold  whilst 
engaged  in  attempting  to  depolarize  one  of  the  ironclads ;  and,  although  he 
partially  recovered,  his  system  received  a  shock  which  ended  in  death.  His 
kind  and  enthusiastic  spirit  was  spared  the  disheartening  report  of  the  non¬ 
success  of  his  method,  subsequently  brought  before  the  Royal  Society. 

Mr.  Barlow  corrects  the  local  magnetic  power  of  the  iron  of  the  ship  by 
placing  a  piece  of  soft  iron  in  a  particular  position,  so  as  to  compensate  for 


SAXBY’S  EXPERIMENTS. 


389 


the  derangement  of  the  compass  produced  by  the  anchors,  chains,  guns,  &c., 
of  the  vessel.  Amongst  the  latest  practical  applications  of  magnetism  to 
useful  purposes  is  that  of  Mr.  Saxby,  who  proposes  to  test  the  iron  of  guns  by 
magnetic  power.  Mr.  Paget,  C.E  ,  in  a  very  able  paper  in  “  The  Engineer,” 
thus  reports  on  the  process  or  method  of  Mr.  Saxby  for  testing  iron : 

“It  is  well  known  to  engineers  that  it  is  a  most  difficult  and  often  impos¬ 
sible  thing  to  find  out  the  existence  of  a  false  weld  in  a  forging,  or  of  a  blow¬ 
hole  or  honeycomb  in  an  iron  or  steel  casting.  The  only  safe  way  of  doing 
this  is  by  carefully  measuring  the  elongation  of  the  piece  under  a  given  load, 
as  with  a  false  w'eld  all  the  work  is  thrown  on  the  diminished  area  at  the 
defective  weld,  and  the  thicker  parts  are  scarcely  extended  by  the  force  which 
is  perhaps  rupturing  the  bar  at  the  flawed  spot.  It  need  scarcely  be  said  that 
there  are  many  important  cases  where  this  process,  or  the  equivalent  but 
dangerous  one  of  trying  the  effects  of  an  impulsive  force,  could  neither  be 
mechanically  nor  commercially  practicable.  Every  one  knows  that  a  simple 
method  by  which  internal  flaws  and  solutions  of  continuity  in  constructive 
details  could  be  easily  detected  would  be  of  enormous  value  to  the  world. 
Such  a  method  has  undoubtedly  been  discovered  by  Mr.  S.  M.  Saxby,  R.N., 
who  has  very  judiciously  been  allowed  by  the  Admiralty,  during  the  course  of 
this  year,  to  experiment  with  it  in  the  royal  dockyards.  Though  compara¬ 
tively  new,  and  not  yet  completely  worked  out,  the  process  will  possibly  have 
a  yet  more  extended  application  than  finding  out  only  mechanical  flaws  in 
iron,  and  possibly  in  cast  iron  and  steel. 

“  The  principle  upon  which  Mr.  Saxby’s  method  is  founded  is  so  simple 
that  it  certainly  seems  strange  that  it  had  previously  escaped  notice.  It  has 
been  known  for  nearly  a  century  and  a  half  that  when  a  bar  or  any  mass  of 
soft  iron  is  placed  in  the  position  of  the  dipping  needle,  it  is  at  once  sensibly 
magnetic,  the  lower  extremity  being  a  north  pole  in  our  latitudes,  and  the 
upper  extremity  a  south  pole.  In  the  southern  hemisphere  the  poles  are  of 
crurse  reversed.  The  same  action,  only  weakened,  takes  place  in  a  bar  hang¬ 
ing  in  avertical 
or  any  other 
position  ;  only 
F.  the  effect  is 
weaker  the 
more  the  posi- 
t  i  o  n  of  the 
longitudinal 
axis  of,  for  in¬ 
stance,  a  long  bar  departs  from  that  of  the  magnetic  dipping  needle. 

“When,  therefore,  as  in  Fig.  329.  a  small  compass  needle  is  slowly  passed 
in  front  of  a  bar  of  very  good  iron,  placed  in  an  east  and  west  direction,  the 
needle  will  not  be  disturbed  from  its  proper  direction,  which  is  of  course  at 
right  angles  to  this,  or  north  and  south. 

“  All  this  refers  to  regularly  homogeneous  bars  of  best  quality— to  bars 
without  any  mechanical  solutions  of  continuity.  With  internal  flaws  or  inter¬ 
ruptions  of  continuity  the  bar  is  no  longer  regularly  magnetic.  It  has  long 
been  known  that  a  good  compass  needle,  or  a  good  permanent  magnet,  must 
be  homogeneous  and  without  flaw's  in  order  to  take  and  retain  its  maximum 
amount  of  magnetism.  In  a  word,  any  mechanical  solution  of  continuity  is 
accompanied  with  a  polar  solution  of  continuity ,  and  the  given  bar  or  mass 
with  flaws — whether  permanently  magnetized  or  temporarily  so  by  the  induc- 


!N 


 A 'J 

u 

;  ? 

5  h  2 

f  j 

► 

S 

Fk;.  3_9 


39° 


MAGNETISM. 


B 

A 

i  +A 

A  1 

y  y 

r  >  n 

Fig.  330. 


tive  action  of  the  earth — is  no  longer  one  regular  magnet,  but  several  different 
magnets,  with  the  different  magnetisms  separated  from  each  other.  The 
delicately-poised  magnet  of  a  compass  can  thus  be  made  to  tell  the  presence 
of  such  solutions  of  continuity.  The  above  drawing  (Fig.  330),  showing  the 
actual  results  of  the  test  with  a  f  in.  bar,  12  in.  long,  will  illustrate  the  manner 
in  which  the  compass  magnet  is  atfected  by  the  presence  of  cracks,  of  solutions 
of  continuity,  in  the  bar,  which  is  supposed  to  be  lying  in  the  equatorial 
magnetic  plane,  or  east  and  west. 

“  By  the  enlightened  permission  of  the  Admiralty  Board,  Mr.  Saxby,  as 
stated,  has  already  been  allowed  to  test  his  method  in  various  ways  in  the 
royal  dockyards  of  Sheerness  and  Chatham,  and  we  will  desciibe  some  of  the 
practical  results  of  these  experiments.  Amongst  these  were  a  number  of  very 
remarkable  trials  conducted  in  the  presence  of  the  master  smiths,  the  foremen 
of  the  testing-houses,  and  several  of  the  chief  engineers  of  the  royal  navy. 


I  IN.SQR. 


IN.SQR. 


BROKE  AT  24  TONS 


0, 


It  ROUND 


BROKE  AT  28  TONS 


00 


I?  ROUND 


ANNEALED 


BROKE  AT  27JT0NS 


li  ROUND 


BROKE  AT  28±  TONS 


^2— 


OFF  SAME  BAR.  AS  D. 

Fig.  331. 


NOT  ANNEALED 


Mr.  Saxby,  for  instance,  was  requested  to  find  out  the  weakest  spots  in  a 
number  of  bars,  and  to  tie  a  string  or  make  a  chalk  mark  on  each  spot. 
Immediately  afterwards  all  these  bars  were  put  into  the  testing  machine  and 
broken.  Their  history  is  given  above,  in  the  annexed  cuts  (Fig.  331),  the 
prediction  having  in  every  case  been  verified.  The  bars  are  shown  by  lines 
to  scale,  and  a  scroll  is  placed  where  the  weakest  part  was  found  out  by  the 
needle.  The  vertical  dotted  lines  indicate  the  spots  where  the  several  bars 
broke. 

1  he  smiths  of  the  royal  dockyards  seem  to  have  properly  tried  Mr.  Saxby’s 
powers  in  almost  every  possible  way,  and  most  ingenious  devices  were  some- 


SAXB  Y'S  EXPERIMENTS. 


39i 


times  resorted  to  for  the  purpose.  As  examples  out  of  many,  in  the  centre  of 
a  bar  (Fig.  332)  of  1  in.  square  forged  iron  was  welded  a  piece  of  unmagnetized 
steel  about  5  in.  long.  The  needle  detected  a  fault  at  about  the  centre  of  the 
piece  of  steel. 

_ LENGTH  12? _ 

-  v  ♦  7  | 

< - 5. 1  NS . > 

Fig.  332. 

“  Now  Mr.  Saxby’s  method  can  detect  the  presence,  and  negatively  of  course 
the  absence,  of  small  or  large  solutions  of  continuity.  It  can  detect  false 
welds,  smaller  flaws  caused  by  bad  workmanship  or  wear,  and,  we  believe, 
what  is  commonly  termed  ‘crystallization,’  which  will,  probably,  at  once  be 
generally  acknowledged  to  consist  in  a  disruption  or  parting  c.f  the  facets  of 
the  amorphously  arranged  crystals  of  which  iron  is  built  up.  It  can,  of  course, 
only  detect  the  results  of  the  chemical  constitution  of  iron,  as  evidenced  in 
the  less  perfect  cohesion  of  the  crystals  when  alloyed,  in  relatively  consider¬ 
able  quantities,  with  foreign  bodies.  There  is  little  doubt  that  the  magnetic 
method  is  a  test  of  the  homogeneous  character  of  the  iron  and  of  its  freedom 
from  fissures  and  cracks,  and  so  far  it  undoubtedly  forms  a  test  of  quality.  It 
will  appear  scarcely  credible  that  a  common  pocket-compass  needle  should 
be  able — almost  like  the  divining  rod  said  to  be  used  for  finding  out  springs 
of  water — to  discover  important  defects  in  large  iron  bars.  A  mere  statement 
of  the  fact  does  sound  almost  incredible  until  the  simple  means  actually 
employed  are  explained.” 

Amongst  the  influences  which  open  the  pores  of  the  steel,  as  it  were,  to 
receive  a  full  charge  of  magnetic  force  is  that  of  heat,  and  it  is  found  that 
when  steel  is  made  red  hot,  and  allowed  to  cool  in  the  direction  of  the  mag¬ 
netic  dip,  it  acquires  more  quickly  and  largely  the  magnetic  charge. 

It  was  contended  by  Mrs.  Somerville  that  unmagnetized  needles  were 
magnetized  if  exposed  to  the  violet  ray  of  the  spectrum  ;  but  Riess  and  Moser 
have  shown  that  these  effects  only  take  place  when  the  needle  is  perpendicular 
to  the  magnetic  meridian,  facilitated  by  the  heating  of  the  needle,  first  by  ex¬ 
posure  to  the  violet  rays,  and  secondly  and  more  especially  by  the  subsequent 
cooling. 

A  powerful  steel  magnet,  heated  to  a  white  heat,  loses  its  magnetic  power. 
Red-hot  iron  is  no  longer  rendered  magnetic  by  induction. 

Nickel,  raised  to  the  temperature  of  boiling  oil,  loses  its  magnetic  virtue. 

It  ought  to  be  mentioned  here,  that  certain  metals,  nickel  and  cobalt,  have 
distinct  magnetic  powers;  and  Sir  Charles  Wheatstone  has  given  a  very  in¬ 
genious  and  elegant  method  of  detecting  minute  quantities  of  magnetic  force. 
He  says — 

“  If  a  short  sewing  needle,  A  (Fig.  333),  the  eye  end  being  broken  off,  rest 
upon  its  point  on  the  polar  surface  of  a  powerful  bar  magnet,  it  will  generally 
take  a  position  inclined  to  the  surface;  but  a  locality  may  generally  be  found 
in  which  the  needle  will  stand  nearly  vertical;  this  point  may  be  ascertained 
by  placing  a  piece  of  unglazed  paper,  D,  between  the  needle  and  the  magnet, 
and  moving  it  about  until  the  vertical  position  of  the  needle  is  obtained. 

“If  we  elevate  the  paper  and  needle  above  the  magnet  to  the  greatest 


392 


MAGNETISM. 


distance  at  which  the  needle  will  remain  vertical,  it  becomes  to  the  last  degree 
sensitive  of  magnetic  force;  so  that  by  bringing  specimens  of  nickel  or  cobalt, 
which  have  the  least  magnetic  power,  or  any  impure  metal,  such  as  a  specimen 
of  metallic  manganese,  which  Faraday  thought  he  had  proved  (when  entirely 
free  from  iron)  does  not  indicate  the  slightest  magnetic  power,*  or  rhodium, 
iridium,  or  hammered  brass,  if  the  latter  metals  contain  any  iron,  they  will 
affect  Wheatstone’s  test  needle,  but  not  otherwise.” 


A 


Fig.  333. 


There  are  other  influences  that  may  affect  the  magnetic  needle.  When  a 
plate  of  copper  is  rotated  quickly  (say  800  revolutions  per  minute)  beneath 
a  suspended  magnet,  the  latter  also  is  thrown  into  rapid  rotation. 


It  might  be  thought  that  this  was  brought  about  by  the  motion  of  the  air; 
but  the  same  effect  occurs  even  when  the  copper  plate  rotates  in  a  vacuum, 
or  is  wholly  screened  by  glass  from  the  magnetic  needle. 


*  See  Dia-magnetism,  for  further  information. 


ROTA TION  EXPERIMENTS. 


393 


The  apparatus  (Fig.  334)  exhibits  this  curious  property  of  metallic  plates  in 
motion,  and  is  usually  made  by  Elliott  with  a  variety  of  metallic  plates,  all 
of  which,  when  spun  round  rapidly,  first  cause  the  magnetic  needle  to  deviate 
from  its  natural  position,  and  then  finally  to  assume  rotation. 

When  the  experiment  is  reversed,  and  a  compound  bent  magnet  is  caused 
to  revolve  with  great  velocity  about  its  axis  of  symmetry,  and  below  the  metallic 
plate,  which  is  carefully  suspended,  then  the  latter  commences  revolving  in 
the  same  direction. 


All  these  experiments  have  arisen  from  the  original  one  performed  by  Arago, 
who  first  tried  the  effect  of  a  ring  of  copper  upon  the  oscillation  of  a  delicate 
magnetic  needle  which  it  enclosed.  In  free  space  the  magnet  performed  4.20 
oscillations  before  it  reached  an  arc  of  lo°,  whereas,  when  surrounded  with 
a  copper  ring,  they  were  reduced  to  fourteen  oscillations  ;  under  the  same 
circumstances  in  a  ring  of  wood,  the  oscillations  were  reduced  from  420  to 
about  300. 


DIA-MAGNETISM. 


Fig.  336. 

Apparatus  made  by  Mr.  Apps, 

Which  maybe  used  either  for  dia-magnetic  expe- 
r  meets  or  to  show  the  enormous  weight  which 
car  he  supported  by  a  powerful  electro-mngr.et. 


In  the  preceding  chapter,  it  has  been 
pointed  out  that  the  loadstone,  iron  and 
steel,  cobalt  and  nickel,  possess  ordi¬ 
nary  magnetic  powers,  and  can  attract 
or  repel  a  magnetic  needle.  We  have 
now  in  the  beautiful  experiments  first 
made  by  Faraday  to  consider  the  mag¬ 
netic  powers  of  other  substances,  and 
shall  discover  that  a  vast  number  of 
bodies  are  affected  by  magnetism  when 
produced  by  and  circulating  from  pole 
to  pole  of  a  very  powerful  electro-mag¬ 
net,  such  as  that  depicted  at  Fig.  336. 

The  dia-magnetic  apparatus  is  spe¬ 
cially  designed  to  illustrate  Faraday’s 
celebrated  experiments  on  the  dia-mag- 
netism  or  para-magnetism  of  bodies, 
and  the  effect  on  light  in  the  rotation 
of  the  plane  of  the  polarized  ray,  &c. 

Besides  these  very  extensive  and 
varied  applications,  the  actual  lifting 
power  of  the  electro-magnet  is  easily 
found  by  turning  the  poles  downwards, 
when  they  face  the  armature  connected 
with  the  compound-lever  arrangement. 
The  power  obtained  with  a  single  cell 
of  Bunsen’s,  of  very  small  size,  will  lift 
5  cwt..  and  with  twenty  Grove’s  cells 
this  magnificent  apparatus  will  lift  3 
tons.  It  was  exhibited  before  the 
Royal  Society,  April,  1868. 

It  should  be  understood  that  all  the 
leading  facts  connected  with  dia-mag- 
netism  may  be  exhibited  to  a  large 
audience  by  a  much  cheaper  apparatus, 
viz.,  by  a  small  electro-magnet  mounted 
so  as  to  be  placed  like  a  magic  lantern 
slide  in  the  oxy-h>drogen  lantern,  when 
the  image  of  the  poles,  brought  as  close 
as  may  be  necessary  by  little  pieces  of 
soft  iron,  is  projected  on  to  the  screen, 
the  movements  of  iron,  bismuth,  cop¬ 
per,  may  be  shown  admirably  ;  and  the 
writer  only  regrets  that  the  illustrious 
discoverer  of  dia-magnetic  phenomena 
did  not  in  this  instance  see  an  illustra¬ 
tion  of  that  which  always  pleased  him, 
viz.,  leading  scientific  truths  illustrated 
by  simple  apparatus. 

In  the  experiments,  which  will  pre¬ 
sently  be  detailed,  there  are  certain  po- 


DIA-MA  GNE  TISM. 


395 


sitions  constantly  referred  to,  i.e.,  the  positions  which  various  bodies  may 
assume  between  the  poles  of  the  electro-magnet  (Fig.  336).  Thus  the  space 
between  the  two  poles  is  called  the  magnetic  field,  and  a  straight  line  drawn 
from  pole  to  pole,  like  the  poles  of  the  earth,  is  called  the  axial  line,  similar  to 

the  imaginary  line  around  which 
the  earth  rotates,  called  its  axis. 
Any  body  subjected  to  the  action 
of  the  magnetic  current  is  said 
to  place  itself  axially  when  it 
takes  the  above  direction.  If, 
however,  the  body  under  experi¬ 
ment  takes  a  position  at  right 
angles  to  this  direction,  it  is  said 
Fig.  337.  to  point  equatona  ly.  Thus,  in 

Fig-  337,  the  poles  are  repre¬ 
sented  by  pieces  of  soft  iron  bevelled  off  to  a  rough  point;  and  if  a  rod  ot  iron 
is  suspended  between  them  and  t  he  electro-magnet  connected  « ith  the  battery, 
the  rod  takes  up  an  axial  position,  whilst  a  similar  rod  of  bismuth,  also 
suspended  by  a  filament  of  silk,  places  itself  at  right  angles  to  that  position, 
as  is  shown  at  Fig.  338. 

In  all  these  ex|  eriments  the  poles  of  the  magnet,  with  their  soft-iron  arma¬ 
tures,  are  surrounded  with  a  glass 
box,  like  the  lantern  of  a  balance, 
to  prevent  the  action  of  currents  of 
air.  Faraday  discovered  that  when 
the  crystals  or  solutions  of  salts  of 
metals  that  are  magnetic,  such  as 
ferrous  sulphate,  are  placed  in  a 
glass  tube  which  is  not  magnetic, 
they  do,  as  a  general  rule,  place 
themselves  axially.  Cobaltous  and 
FlG.  338.  nickelous  sulphate  behave  in  the 

same  manner  ;  and  this  axial  posi¬ 
tion  is  always  maintained,  provided  the  metal  enter  into  the  basyl  of  the 
salt. 


Fig.  339.  —  The  Cube  of  Bismuth  taking  the  Equatorial  position. 


When  a  single  pole  of  the  electro-magnet  is  used,  repulsion  takes  place 
with  very  many  bodies,  and,  of  course,  if  the  substance  is  repelled  by  both 
poles  when  placed  in  the  magnetic  field,  it  will  take  a  place  at  right  angles  to 
the  magnetic  current,  or  the  ecjuatoiial  position. 


MAGNETISM. 


396 


Phosphorus,  bismuth,  and  antimony  —  the  first  a  non-conductor  of  elec¬ 
tricity,  and  the  second  and  third  metals  therefore  conductors — are  each  and 
all  repelled  from  a  single  pole,  or  place  themselves  in  the  equatorial  position 
between  the  two  poles. 

It  is  most  amusing  to  twirl  a  suspended  halfpenny  between  the  poles  of  the 
electro-magnet  (Fig.  340).  Of  course  this  may  be  done  as  often  or  as  long 
as  the  experimenter  pleases ;  but  if,  whilst  the  coin  is  rotating,  the  electro¬ 
magnet  is  connected  with  the  battery,  the  halfpenny  stops  dead,  and  instantly 
places  itself  in  the  equatorial  position. 


Fig.  3  p. —  The  Halfpenny  twirled, ,  the>i  stopped  by  the  magnetic  force. 

The  preceding  experiments  show  that  those  bodies  which  are  not  magnetic 
will  exhibit  dia-magnetic  properties,  /.<?.,  they  are  substances  through  which 
the  lines  of  magnetic  force  (represented  by  the  beautiful  curves  assumed  by 
iron  filings  when  sprinkled  on  a  sheet  of  cardboard  held  over  the  poles  of  a 
powerful  magnet  or,  still  better,  an  electro-magnet)  pass  without  affecting  them 
like  iron,  cobalt,  or  nickel. 

This  mode  of  experimenting  is  more  delicate  as  a  test  for  magnetism  than 
the  use  of  the  needle,  already  alluded  to  at  page  362,  Fig.  333. 

And  it  was  by  taking  solutions  of  pure  salts  of  manganese  and  chromium, 
and  placing  them  in  the  magnetic  field,  that  they  were  discovered  to  be  mag¬ 
netic,  whilst  as  metals  it  was  so  difficult,  if  not  almost  impossible,  to  obtain 
them  in  the  pure  state  and  free  from  iron.  (Fig.  341.) 


Fig.  341. 


Faraday,  always  so  exact  and  orderly  in  his  classification  and  nomenclature, 
proposes  to  include  all  the  phenomena  under  one  general  title,  viz.,  that  of 
magnetism,  and  to  subdivide  this  into  para-magnetic  and  dia-magnetic  phe¬ 
nomena.  A  very  long  list,  originating  with  Faraday,  has  therefore  been  framed 
un  this  principle. 


DIA-MA  GATE  TISM. 


397 


r.tra-M.ijnctic,  usua.lv 
calli.il  Magnetic. 

Axial. 

Manganese 

Nickel 

Cobalt 

Iron 

Titanium 

Palladium 

Cerium 

Chromium 

Platinum 

Osmium 

Paper 

Sealing-wax 
Berlin  porcelain 
China  ink 
Plumbago 
Peroxide  of  iron 
Fluor  spar 
Asbetos 
Silkworm  gut 
Red  lead 


Dia-Magnetic. 

Equatorial 

Lead 

Cadmium 

Sodium 

Mercury 

Zinc 

Tin 

Bismuth 

Antimony 

Arsenic 

Silver 

Gold 

Copper 

Tungsten 

Uranium 

Rhodium 

1  ridium 

Alum 

Glass 

Rock  crystal 
The  mineral  acids 
Nitn 


Tara- Magnetic,  usually 
called  Magnetic. 

Axial. 

Sulphate  of  zinc 
Shellac 

All  sorts  of  iron,  \ 
where  the  latter  ;> 
is  basic  ; 

Vermilion 
Tourmaline 
Charcoal 

Oxygen,  which  i 
stands  alone  as  ' 
a  para-magne-  y 
tic  gas  ' 

Salts  of  chromium 
Salts  of  manga-  I 
nese  ( 

Oxide  of  titanium 
Oxide  of  chro-  ) 
mi  u  m  \ 

Chromic  acid. 


Dia-Magnetic. 

Equatorial. 

Litharge 
Phosphorus 
Common  salt 
N  itre 
Sulphur 
Resin 

Spermaceti 
Iceland  spar 
Tartaric  acid 
Citric  acid 
Water 
Alcohol 
Ether 
Sugar 
Starch 
Gum  arabic 
Wood 
ivc.,  &c. 


Nitrogen  is  like  a  vacuum — it  is  neither  para-magnetic  nor  dia-magnetic  ;  it 
is,  in  strict  reason,  like  space,  with  reference  to  these  experiments  ;  it  is  a  zero, 

or  a  starting-point. 

The  magnetic  or  dia-magnetic  property  of  a  body,  curious  to  say,  varies 
according  to  the  medium  in  which  it  is  placed:  thus,  a  glass  rod,  suspended 
horizontally  in  water,  which  we  find,  with  glass,  in  the  dia-magnetic  column, 
points  axially,  like  any  ordinary  magnetic  body;  but  if  the  same  glass  rod  is 
suspended  in  a  solution  of  ferrous  sulphate,  a  magnetic  body,  it  points  equa- 
torially. 

The  magnetic-field  test  discovers  whether  a  metallic  salt  has  the  metal  in 
the  basyl,  the  basic,  or  electro-positive  state;  or  whether  the  metal  is  simply 
a  part  or  constituent  of  the  acid  or  electro-negative  compound.  Iron  is  basyl 
in  ferrous  sulphate,  and  sets  axially,  and  is  para-magnetic;  but  in  potassic 
ferrocyanide  it  forms  part  of  the  ferrocyanic  acid,  and  therefore  the  crystal 
sets  equatorially,  and  is  dia-magnetic.* 

The  reader  will  find  all  the  apparent  exceptions  and  peculiarities  attending 
their  structure  in  Tyndall  and  Knoblauch’s  paper  (Phil.  Mag.,  1850,  vol.  xxxvi., 
p.  178,  and  xxxvii.,  p.  1).  The  same  gentlemen  have  discovered  that  dia¬ 
magnetic  repulsion  is  as  the  square  of  the  intensity  of  the  current ;  and  Reich, 
Weber,  and  Tyndall  seemed  to  have  proved  that  which  foiled  Faraday,  viz., 
that  bodies  under  dia-magnetic  influence  exhibit  polar  characters.  The  polarity 
is  the  reverse  of  all  other  polarities,  electrical  or  magnetic:  the  feeble  polarity 
of  a  dia-magnetic  substance  is  the  same  as  the  pole  of  the  magnet  in  its  neigh- 


*  The  Mmt  test  w  II  discover,  lor  Instance,  in  a  roll  of  paper,  whether  it  contains  iron  or  not:  il 
1  contains  the  metal,  or  is  coloured  bine  with  cobalt,  it  will  sci  axiallv,  because  iro  1  and  cobalt  aie 
magnetic  oi,  to  use  Faraday’s  pnrascology,  para-magnetic. 


39§ 


MAGNETISM. 


bourhood ;  whereas  we  have  learnt  that  north  induces  south  magnetism  in  a 
piece  of  iron,  and  vitreous  electricity  induces  negative  in  the  body  to  which 
it  is  approached. 

The  dia-magnetism  of  gases  was  first  shown  by  F ather  Bancalari,  of  Genoa, 
who  discovered  that  flame,  such  as  the  flame  of  a  candle,  was  influenced  by 
the  poles  of  a  powerful  electro-magnet. 


Fig.  342. — Effect  of  the  Poles  on  Flame. 


Faraday  tried  Bancalari’s  experiment,  and  found  that  when  the  axial  line  of 
die  magnet  was  horizontal,  and  the  flame  of  a  taper  held  near  it,  and  on  one 
side  or  the  other,  with  about  one-third  of  the  flame  rising  above  the  level 
of  the  upper  surface  of  the  poles,  the  flame  seemed  to  be  repelled  away  from 
the  axial  line,  moving  equatorially  until  it  took  an  inclined  position,  as  if  a 
gentle  wind  was  acting  upon  it,  and  causing  its  deflection  from  the  perpendi¬ 
cular  line. 

It  was  the  flame  experiments  which  led  to  the  discovery  of  the  magnetic 
property  of  oxygen,  and  of  the  dia-magnetic  properties  of  atmospheric  air, 
nitrogen,  hydrogen,  coal  gas,  olefiant  gas,  &c. 

Faraday  showed  that  soap-bubbles,  filled  with  various  gases  and  blown 
from  the  end  of  a  capillary  tube,  were  either  attracted  or  repelled  according 
as  the  gas  was  magnetic  or  dia-magnetic. 


Fig.  343. — Melting  Fusible  Metal  between  the  Poles  of  the  great 

Electro-Magnet. 


One  of  the  most  curious  experiments  which  may  be  performed  with  the  dia¬ 
magnetic  apparatus  is  that  of  overcoming  the  equatorial  or  para-magnetic 
force  by  physical  power.  The  twirled  penny-piece  brought  to  rest  between 
the  poles,  if  forcibly  turned  round,  will  by  the  motion  generate  heat,  and  may 
be  made  very  hot. 


DIA-MA  GNE  TISM. 


399 


If  a  brass  tube,  containing  some  solid  fusible  metal,  composed  of  two  parts  bv 
weight  of  bismuth,  one  of  lead,  and  one  of  tin,  with  a  few  drops  of  mercury,  is 
rotated  very  fast  by  a  whirling-table  wheel  between  the  poles  of  the  powerful 
magnet,  no  effect  is  produced  until  contact  is  made  with  the  battery,  and  then 
the  rotation  or  motion  is  speedily  converted  into  heat,  and  the  fusible  metal  is 
melted  as  if  it  had  been  held  over  the  fire.  Here  again  is  a  perfect  conservation 
of  force.  The  heat  which  melted  the  alloy  is  the  exact  equivalent  of  the 
chemical  power  of  the  battery  used,  although  it  acts  by  an  intermediate  force, 
viz.,  magnetism;  but  the  chemical  action  produced  the  electricity,  the  current 
electricity  produced  the  magnetism,  and,  the  magnetic  force  which  tends  to 
keep  the  bismuth  in  the  alloy  in  the  equatorial  position  being  overcome  and 
resisted  by  physical  force,  the  muscles  of  the  arm  acting  on  the  whirling  table 
eliminate  heat. 

Faraday  thought  he  had  proved,  by  using  heavy  glass  and  permitting  a 
ray  of  polarized  light  to  pass  through  it,  that  the  ray  was  affected  by  the 
powerful  magnetic  force  eliminated  from  the  great  electro-magnet.  Faraday’s 
glass  consists  of  a  mixture  of  silicate  and  borate  of  lead,  and  is  much  denser 
than  ordinary  glass.  If  a  ray  of  polarized  light  is  allowed  to  pass  through  it, 
and  is  then  examined  in  the  ordinary  manner  with  an  analyzing  plate  or  a 
bundle  of  plates  of  glass,  or  by  a  tourmaline  or  a  N  icol’s  prism,  the  light,  of 
course,  disappears,  as  already  explained  in  the  article  on  Light,  when  the  plane 
of  refection  from  the  analyzing  plate  is  at  right  angles  to  the  plane  of  polari¬ 
zation.  (Fig.  344.) 


Fig.  344. 


If  now  the  battery  is  connected  with  the  electro-magnet,  between  the  poles 
of  which  the  bar  or  cube  of  Faraday’s  dense  glass  is  placed,  the  light  re-appears 
instantly,  again  disappearing  when  contact  is  broken  with  the  battery. 

Matteuchi  found  that  the  effect  was  increased  by  increasing  the  temperature 
of  the  cube  of  heavy  glass  to  6oo°  Fahrenheit;  and  he  also  ascertained  that 
by  subjecting  the  heavy  glass  to  pressure  he  could  change  the  direction  of  the 
ray  of  polarized  light,  as  Faraday  had  done.  So  that,  in  fact,  Faraday  was 
wrong;  the  magnetic  force  did  not  act  upon  the  ray  of  polarized  light,  but  on 
the  molecules  or  particles  of  the  glass,  which  were  under  a  strain  during  the 
time  they  were  subjected  to  the  action  of  the  powerful  electro-magnetic  force. 


400 


MAGNETISM. 


Fig.  345  ,—  Apps’s  half-horse  power  Electro-Magnetic  Engine. 


ELECTRO-MAGNETISM,  MAGNETO-ELECTRICITY. 
THERMO-ELECTRICITY. 

In  1 820,  (Ersted,  a  Danish  scientific  man,  discovered  the  connection  between 
electricity  and  magnetism.  It  was  not  found  where  philosophers  sought  for  it. 
They  thought  to  imitate  Nature;  and  as  some  steel  knives  were  found  to  be 
powerfully  magnetic  after  a  discharge  of  lightning  had  passed  through  a  box 
containing  them,  they  subjected  other  pieces  of  steel  to  the  discharge  of 
powerful  Leyden  batteries  without  producing  the  effect  they  expected. 

(Ersted  found  that  the  electricity  must  be  in  motion,  or  in  a  dynamical  state, 
such  as  it  would  be  in  when  evolved  from  the  voltaic  batter). 

Static  electricity  will,  under  certain  arrangements  to  be  hereafter  described, 
magnetize  steel ;  but  the  mere  fact  of  allowing  a  wire  charged  with  statical 
electricity  (the  force  from  the  electrical  machine)  to  approach  a  magnetic 
needle  does  not  affect  the  needle  like  the  same  wire  conveying  a  current  from 
a  single  voltaic  circuit  or,  still  better,  a  battery. 

M.  Ampere,  who  took  up  the  subject  directly  after  (Ersted  had  published 
his  discoveries,  laid  the  foundation  of  the  science  of  electro-dynamics.  He 
discovered  that  every  part  of  the  whole  circuit — the  wires,  the  terminals  or 
poles,  the  battery,  in  fact,  all  parts — exercised  a  magnetic  power  upon  the  mag¬ 
netic  needle.  He  also  proved  that  the  force  was  in  an  eminent  degree  one  of 
circulation.  Ampere  made  himself  fully  understood  by  asking  his  readers  to 
conceive  a  man  lying  down  in  the  circuit,  so  that  the  wire  lies  along  his  face 


ELECTR  O-MA  GNETISM. 


401 


and  body.  We  are  now  to  suppose  that  the  current  enters  the  wire  at  his  feet 
and  goes  out  at  his  head,  and  that  his  upturned  face  and  eyes  are  directed  to  a 
magnetic  needle  suspended  parallel  with  and  over  the  wire  conveying  the 
electric  current,  so  that  the  north  pole  of  the  needle  points  to  his  face. 
Directly  the  current  passes,  the  needle  is  deflected  to  his  left  hand;  and  by 
reversing  the  direction  of  the  current,  and  causing  it  to  flow  into  the  wire  at 
his  head  and  out  from  his  feet,  the  needle  will  now  move  to  his  right  hand. 


Fig.  346. —  Wire  conveying  a  Current  of  Electricity  affecting  the  Magnetic 

Needle. 


Thus  every  possible  variation  may  be  imagined  as  long  as  we  maintain  the 
same  relative  positions  of  the  wire  and  the  human  body ;  and  it  was  further 
ascertained  that  the  intensity  of  the  electro-magnetic  force  is  in  the  inverse  ratio 
to  the  simple  distance  of  the  magnetic  needle  from  the  current;  or,  in  other 
words,  that  the  elementary  action  of  a  simple  section  of  the  current  upon  the 
needle  is  in  the  inverse  ratio  to  the  square  of  the  distance. 

If  a  single  wire  can  affect  a  magnetic  needle,  it  is  evident  that  by  doubling 
and  trebling  the  wire,  or  winding  it  round  in  a  helix,  the  effect  must  be 
enormously  increased,  provided  the  coils  of  wire  do  not  touch  each  other,  or 
are  covered  with  some  non-conducting  material,  such  as  silk  or  cotton  ;  hence 
it  is  that  coils  of  wire  are  constructed  so  that  a  piece  of  soft  iron  placed 


Fig.  347- 


inside  the  core  becomes  a  most  powerful  magnet  directly  contact  is  made 
H'ith  the  battery.  When  the  immense  power  of  the  electro-magnet  was  ascer- 


402 


* 


MAGNETISM. 


tained,  great  anticipations  were  formed  of  the  application  of  this  force  as  a 
motive  power.  It  is  not  surprising  that  this  should  have  been  the  first  con¬ 
clusion.  Thus  the  great  electro-magnet,  made  by  Mr.  Apps,  that  heads  the 
chapter  on  Dia-magnetism,  will  lift  five  hundredweight  with  a  single  quarter- 
pint  Grove’s  cell,  and  three  tons  with  twenty  cells.  This  conveniently  arranged 
magnet,  after  being  used  for  dia-magnetic  experiments,  may  be  employed  for 
showing  the  attractive  force  of  the  great  electro-magnet.  It  is  attached  to  a 
lever,  which  turns  it  over ;  and,  when  suspended  with  the  poles  downwards, 
it  is  connected  with  a  compound-lever  arrangement,  on  the  same  principle 
as  railway  weighing-machines,  and  the  weights  used  are  one  quarter,  one  half, 
and  one  hundredweight. 

The  writer  well  remembers  the  late  Prince  Consort,  on  the  occasion  of  one 
of  his  private  visits  to  the  Polytechnic,  putting  a  question  to  him  as  to  the  rate 
at  which  the  electro-magnetic  power  increased  or  decreased  with  the  distance 
from  the  great  electro-magnet  belonging  to  the  Polytechnic.  The  attractive  force 
diminishes  enormously.  Thus,  in  a  paper  read  by  Mr.  Robert  Hunt  before  the 
Institution  of  Civil  Engineers,  the  following  instructive  diagram  was  exhibited: 


Fig.  348. 


It  is  shown  that,  whilst  contact  gave  a  power  of  220  lb.,  at  a  distance  of  jtj 
of  an  inch  the  attractive  force  diminished  to  36  lb. 


Fig.  349 .—A  Dextrorsal  and  a  Sinistrorsal  Helix . 

It  is  found  that  by  encasing  ail  electro-magnet  with  a  tube  of  soft-iron,  that 


ELECTRO-MA  GNETISM. 


4°3 


the  power  is  gre  tly  increised.  Tubular  electro-magnets  were  first  made  in 
Germany  in  1850  bv  Komershausen,  who  found  that  an  external  soft-iron  tube 
increased  the  carrying  power  of  an  electro-magnet,  with  an  iron  core  09  cm. 
in  diameter  and  8‘4  cm.  long,  sixty-four- fold  !  Mr.  Apps  has  some  electro¬ 
magnets  ot  peculiar  construction,  in  which  the  system  is  arranged  in  3  or  4 
concentric  soft-iron  tubes  starting  from  an  iron  core.  One  series  of  four  is 
capable  ot  sustaining  1  cwt.  at  a  distance  of  1  in.,  and  6  cwt.  at  a  quarter  of 
an  inch.  I  he  diameter  ot  this  tubular  electro-magnet  is  6  in.,  and  the  length 
9.  Mr.  Faulkner  has  called  special  attention  to  electro-magnets  of  this 
construction,  and  called  them  altandae  electro-magnets. 


When  a  wire,  traversed  by  an  electric  current,  is  held  in  iron  filings,  they 
adhere  to  it  as  long  as  the  current  passes.  If  the  wire  is  coiled  upwards  round 
a  glass  tube  Irom  left  to  right,  it  is  called  a  dextrorsal  helix  ;  and  if  coiled 
downwards,  and  in  the  same  direction,  it  is  teimed  a  sinistrorsal  helix. 

A  piece  of  steel  p’aced  inside  such  a  helix,  containing  the  voltaic  current,  is 
soon  magnetized.  If  the  same  coil  is  used  to  convey  the  charge  from  a  Leyden 
battery  of  6  ft.  surface,  a  piece  of  steel  is  instantly  magnetized.  Electricians 
had  missed  this  form  of  the  experiment  until  (Ersted’s  discovery. 

If  a  bar  magnet  be  held  so  that  it  is  horizontal,  and  the  north  pole  directed 
to  the  vertical  portion  of  the  rectangular  wire,  so  supported  that  whilst  convey¬ 
ing  the  electric  current  it  moves  freely  round  in  a  circle  (Fig.  350),  it  will  be 
found  that,  if  the  upright  portion  of  the  wire  is  conveying  the  current  from 
below  upwards,  it  is  repelled,  but  attracted  if  the  south  pole  is  substituted  ; 
and  thus,  by  the  dexterous  substitution  of  one  pole  for  another  in  presenting 
the  bar  magnet  to  the  rectangular  wire,  it  may  be  caused  to  rotate. 

Polarity  is  shown  by  the  sides  of  the  wire,  whereas  in  steel  magnets  it  is 
discoverable  at  the  ends. 

The  same  attraction  and  repulsion  occurs  if  another  electrified  wire  is  brought 
towards  the  suspended  rectangular  wire  whilst  conveying  the  electrical  current. 

Fig.  351  is  a  good  illustration  of  the  direction  of  the  current  circulating 
around  each  section  of  a  magnet  everywhere  in  the  same  direction,  viz.,  from 
top  to  bottom  in  the  face  that  is  turned  towards  the  moving  wire,  and  from 

2G — 2 


404 


MAGNETISM. 


bottom  to  top  in  that  which  is  opposite  to  it.  The  sum  of  these  directions 
amounts  to  a  current. 

A  similar  result  is  obtained  when  a  horizontal  wire  is  directed  to  a  magnet 

suspended  vertically.  The  magnetic 
currents  circulating  around  the  mag¬ 
net  are  again  shown  by  arrows.  A 


Fig.  352. — Magnet  suspended  in  a 
Perpendicular  line ,  the  Curre?it 
flowing  horizontally. 


magnet  may,  therefore,  says  De  la 
Rive,  be  considered  as  formed  by  an 
association  of  electric  currents,  all  cir¬ 
culating  in  the  same  direction  around 
its  surface,  and  all  situated  in  planes  parallel  to  each  other,  and  perpen¬ 
dicular  to  the  axis  of  the  magnet.  It 
is  this  hypothesis  of  Ampere  of  the 
constitution  of  magnets,  shown  in 
Figs  351  and  3 52,  and  which  explains 
CErsted’s  original  experiment,  and 
also  all  those  that  relate  to  the  devia¬ 
tion.  In  order  to  confirm  the  hypo¬ 
thesis  to  which  he  had  been  led,  of 
the  nature  of  magnetism,  Ampere 
endeavoured  to  arrange  electric  cur¬ 
rents  in  the  same  manner  as  he 
had  conceived  they  were  naturally 
arranged  in  a  magnet.  Thus  a  flat 
spiral  coil  of  wire  (Fig.  333),  nicely 
supported  and  resting  on  points,  and 


Fig.  354. — Magnet  revolving  around 
Wire  co7iveying  the  Current. 

perfectly  mobile,  takes  a  position  perpendicular  to  the  magnetic  meridian. 

By  reversing  the  experiment,  and  causing  the  wire  to  be  fixed,  and  the  magnet 


ELECTR  O-MA  G  NET  ISM. 


4°  5 


to  revolve  around  it  (Fig.  354),  further  proof  was  obtained  by  Faraday  of  the 
mutual  relations  between  magnets  and  wires  conveying  the  voltaic  current. 
In  this  case  we  have  the  revolution  of  one  pole  of  a  magnet  about  a  verti¬ 
cal  wire  transmitting  a  rectilinear  current.  The  direction  of  rotation  is 
reversed  each  time  the  direction  of  the  current  is  reversed. 

Or  the  experiment  may  be  again  modified  and  reversed  by  supporting  (as 
with  the  apparatus  made  so  nieely  by  Messrs.  Elliott)  two  helices  or  coils  of 
copper  which  are  made  to  convey  the  voltaic  current,  and  rotate  in  opposite 
directions  around  the  pc’es  of  the  horse-shoe  magnet,  as  show  n  in  Fig.  355. 


Fig.  355. — Contrary  Rotation  of  two  helical  Fig.  356. 

Coiled  Wires  around  the  Roles  of  a  Magnet . 


This  apparatus  is  usually  called  Ritchie's  spirals.  De  la  Rive  says  Ampere 
succeeded  in  overcoming  all  objections  to  his  theory,  and  established  it  on 
such  a  solid  basis  that  it  is  at  the  present  time  generally  admitted.  He  set 
out  from  the  principle  that  the  electric  currents  to  which,  according  to  his 
view,  magne  s  owe  their  properties  are  molecular,  that  is,  that  they  circulate 
around  each  particle.  These  electric  currents  pre-exist  in  all  magnetic  bodies 
|  even  although  they  have  not  been  magnetized,  only  they  are  arranged  in  an 
irregular  manner,  so  that  they  neutralize  each  other.  Magnetization  is  the 
I  operation  by  which  a  common  direction  is  impressed  upon  them  ;  whence 
it  follows  that  the  series  of  the  exterior  portion  of  the  molecular  currents, 
which  are  all  moving  in  the  same  direction,  constitutes  a  finished  current  . 
around  the  magnet,  whilst  the  interior  portions  are  neutralized  by  the  exterior 
ones,  moving  in  the  contrary  direction,  of  the  following  molecular  stratum. 

Fig.  356  represents  the  .ection  of  a  cylinder  magnet  and  the  magnet  itself. 
The  direction  impressed  upon  the  currents  by  magnetization  is  maintained  in 
[  bodies  that  are  endued  will  coercitive  force,  and  ceases  in  others,  such  as 
j  soft  iron,  as  soon  as  the  force  that  determined  it  ceases,  because  then  all  the 
'  molecular  currents,  being  free  to  obey  their  mutual  action,  take  the  relative 
position  that  produces  equilibrium,  or  the  neutralization  of  every  exterior  effect. 


MAGNETISM. 


406 


To  Faraday  is  due  the  credit  of  realising  the  idea  that  the  mutual  reaction 
of  magnets  or  wires  conveying  electrical  currents,  and  vice  versa ,  should  pro¬ 
duce  rotation ;  and  he  was  the  first  to  cause  a  wire  conveying  a  current  to 
revolve  around  a  magnet,  and  the  latter  to  rotate  about  a  wire  through  which 
the  voltaic  current  is  passing. 

These  original  and  philosophical  experiments  have  been  extended  to  larger 
apparatus,  and  various  attempts  have  been  made  to  use  the  electro-magnetic 
rotation  successfully:  Dal  Negro,  1832;  Professor  Botto  and  Professor  Jacobi 
in  1835  ;  Mr.  Thomas  Davenport,  of  the  United  States,  in  1837  ;  and  Mr.  Taylor 
in  1839. 

Davidson,  in  1837,  placed  an  electro-magnetic  locomotive  on  the  Edinburgh 
and  Glasgow  Railway.  The  carriage  was  16  ft.  long  and  6  ft.  broad,  and  weighed 
about  5  tons,  with  all  the  arrangements;  but,  when  put  in  motion,  a  speed  of 
only  4  miles  per  hour  could  be  obtained. 

Professor  Page  constructed  an  electro-magnetic  engine  which  created  much 
interest  at  the  time,  and  he  calculated  that  the  consumption  of  3  lb.  of  zinc  per 
diem  was  equal  to  one  horse  power.  Page’s  engine  was  followed  by  those  of 
Talbot  and  Wheatstone. 

Mr.  Hjorth  exhibited  in  London  an  engine  which  found  many  admirers. 
The  attractive  force  of  Hjorth’s  machine  is  thus  given  by  Mr.  Hart,  from 
whose  valuable  paper  the  above  historical  details  are  taken  : 


72 

lb. 

80 

88 

124 

140 

160 

Fig.  35 7. — Hjorth' s  Principle. 


but,  like  the  rest,  it  was  abandoned. 

Dr.  Botto  states  that  45  lb.  of  zinc  consumed  in  a  Grove’s  battery  are  suffi¬ 
cient  to  work  a  one-horse  power  electro-magnetic  engine  for  twenty-four  hours. 

Mr.  J.  P.  Joule  calculates  that  the  same  result  would  have  been  obtained 
by  the  consumption  of  75  lb.  of  zinc  in  a  Daniell’s  battery.  Mr.  Joule  and 
Dr.  Scoresby  thus  sum  up  a  series  of  experimental  results : — “  Upon  the  whole, 


ELECTRO-MA  GNETISM. 


407 


we  feel  ourselves  justified  in  fixing  the  maximum  available  duty  of  an  electro¬ 
magnetic  engine,  worked  by  a  Daniell’s  battery,  at  80  lb.  raised  one  foot  high 
for  each  grain  of  zinc  consumed.  This  is  about  one-half  of  the  theoretical 
maximum  duty.  In  the  Cornish  engines  doing  the  best  duty,  one  grain  of  coal 
raised  143  lb.  one  foot  high.  Zinc  is  worth  about  ^35  per  ton,  and  engine  coal 
is  worth  less  than  £\  per  ton,  delivered  in  London.  Comment  upon  this  is 
unnecessary. 

The  fact  is,  an  electro-magnetic  engine  is  a  very  pretty  toy,  and  can  be 
used,  like  Mr.  Apps’s  half-horse  power  engine  (Fig.  345,  p.  4oj),  to  turn  a 
small  lathe,  or  propel  a  small  boat,  or  turn  whirling  tables  or  other  apparatus 
on  the  lecture- table,  i.e.,  where  the  cost  of  zinc  and  acids  from  the  battery  is 
of  no  consequence.  Mr.  Apps  furnishes  the  following  particulars  of  the  above- 
named  electro  magnetic  engine : 

“  Weight  80  lb.  When  driven  to  400  revolutions  per  minute  by  20  cells 
Grove  (platina  6  in.  X  3  in.),  a  half-horse  power  is  obtained.  It  will  drive  with 
equal  facility  in  either  direction,  or,  on  reversing  the  current  by  the  douLle 
commutator,  the  magnetic  power  produced  is  opposite  to  the  momentum 
previously  acquired  (acting  like  a  friction  brake)  ;  the  direction  of  rotation  is 
reversed,  and  in  about  three  seconds  the  former  rate  of  speed  is  acquired. 

■‘Avery  important  point  is  gained  in  this  machine.  The  current  being 
gradually  broken,  the  spark  usually  produced  at  the  breaking  of  the  contact  is 
avoided,  besides  this  great  advantage,  the  residual  magnetism  is  destroyed, 
which  alone  in  the  old  machines  diminished  their  power  by  at  least  one- 
quarter.  The  machine  is  well  adapted  to  drive  a  lathe  or  the  screw  propeller 
of  a  small  boat.” 

If  electro-magnetic  motion  cannot  compete  with  steam  power,  it  may,  how¬ 
ever,  be  applied  usefully  in  other  ways,  as  in  Edison’s  “  Electric  Pen.”  The 
object  of  this  pen  is  to  pierce  fine  holes  in  sheets  of  paper,  forming  stencils, 
from  which  impressions  are  taken.  This  is  done  when  the  stencil  is  once 
prepared,  by  passing  an  inked  roller  over  the  stencil,  which  prints  on  to  the 
paper  placed  beneath  it.  As  many  as  1,000  to  2.000  impressions  can,  it  is 
asserted,  be  thus  printed  at  the  rate  of  four  to  six  per  minute.  The  movement 
of  the  needle  that  makes  the  tiny  holes  in  the  paper  is  due  to  the  rapid  motion 
of  the  armature  of  an  electro-magnet,  steadied  by  attachment  to  a  small  fly¬ 
wheel.  The  battery  consists  of  two  ordinary  bichromate  ceils,  which  can  be 
placed  in  or  out  of  action  at  pleasure,  or  Fuller’s  new  form  of  bichromate 
battery,  which  dispenses  with  the  lifting  of  the  plate  in  or  out  of  the  exciting 
fluid,  and  is  likely  to  come  into  use  in  connection  with  the  electric  pen.  A 
set  of  apparatus  complete  costs  eight  guineas. 


408 


MAGNETISM. 


MAGNETO-ELECTRICITY. 


INDUCTION  BY  CURRENT  ELECTRICITY. 

It  has  been  noticed  that  a  current  of  electricity  elicits  magnetism,  and 
therefore  it  is  not  surprising  that  the  effect  should  be  reversible  ;  but,  simple  as 
this  may  appear  in  theory,  it  was  a  long  time  before  Faraday  succeeded  in 
overcoming  the  difficulties  he  encountered,  and  was  enabled  to  relate  his  suc¬ 
cess  in  the  “  Philosophical  Magazine,  1332,  page  125. 

The  extremities  of  a  helix  or  large  hollow  bobbin  of  wire  were  connected 
with  the  galvanometer  needle,  care  being  taken  that  the  galvanometer  should 
not  be  near  enough  to  be  affected  by  the  magnet  which  Faraday  used. 


Fig.  358. — Faraday’s  first  Experiment. 

The  movement  of  the  bar  magnet  across  the  coils  produced  a  current 
which  affected  the  needle,  and  still  better  when,  as  in  Fig.  358,  the  magnet 
was  intruded  into  the  axis  or  hollow  of  the  bobbin  or  helix.  Not  only  is  the 
needle  deflected  when  the  magnet  is  insulated,  but  it  is  also  moved  in  an 
opposite  direction  when  the  magnet  is  removed. 

\Y  hen  two  concentric  helices,  of  course  of  insulated  or  covered  wire,  are 
arranged,  the  inner  one  being  of  thicker  wire  than  the  outer,  and  wound  round 
an  axis  or  core  of  soft  iron,  a  very  powerful  secondary  current  is  obtained  in 
the  outer  coil  when  the  inner  core  is  magnetized.  Such  currents  are  called 
induced  currents,  and  are  always  more  powenul  when  soft  iron  forms  the  axis 
or  core,  because  the  iron,  in  acquiring  or  losing  magnetism,  produces  a 
secondary  current  which  occurs  in  the  same  direction  as  that  induced  by  the 
inner  coil  or  helix. 

Here,  then,  is  a  distinct  excitation  or  elimination  of  electricity  by  magnetism 
alone,  and  is  called  magnetic  electric  induction  to  distinguish  it  from  volta- 
electric  induction,  also  investigated  by  Faraday,  and  brought  before  the  Royal 


MA  GNETO-ELEC  TRICITY. 


40-9 


Society  in  1831.  In  the  latter  experiments,  two  great  coils  of  wires  were, 
wound  together,  metallic  contact,  of  course,  being  prevented.  One  coil  was 
connected  with  the  galvanometer,  and  the  other  with  the  voltaic  battery. 
The  induced  electricity  in  the  second  coil  was  suddenly  produced  like  a  wave, 
presenting  a  marked  difference  to  the  magneto-electric  induction,  which  was 
much  slower  in  its  production.  Here,  then,  are  two  modes  of  induction: 

1.  VOLTA-ELF.CTRIC  INDUCTION; 

2.  MAGNETO-ELECTRIC  INDUCTION. 

The  magneto-electric  induction  has  been  applied  to  the  production  of  cur¬ 
rents  of  electricity  by  Pixii — the  first  in  Paris,  1832,  followed  by  Saxton  and 
E.  M.  Clarke. 

Such  instruments,  in  which  a  powerful  compound-mag¬ 
net,  having  rotating  in  front  of  its  poles  an  armature  or 
bobbin  of  fine  wire  (which  may  be  varied  to  produce 
either  quantity  or  intensity  effects),  elicits  a  current  that 
can  be  made  to  illustrate  physiological,  mechanical,  che¬ 
mical,  and  ordinary  electrical  effects,  are  so  fully  described 
in  every  book  on  electricity  that  the  writer  prefers  to  pass 
to  newer  and  more  perfect  arrangements. 

Magneto-electricity  was  applied  and  exhibited  by  Mr. 

Holmes  in  the  Great  Exhibition  of  1862,  and  obtained 
from  a  machine  of  novel  construction.  At  the  same  Ex¬ 
hibition,  and  also  in  Paris,  1867,  the  w'riter  saw  Nollet’s 
machine  as  improved  by  Mr.  van  Malderen,  who  took 
great  pains  to  show  the  w^riter  the  construction  of  his  magneto- electric  ma¬ 
chine  for  light-giving  purposes ;  and  it  was  understood  that,  at  a  cost  of  ^30 o, 
one  of  these  machines,  turned  by  a  steam-engine,  might  supply  the  Polytechnic 
with  the  electric  light  at  any  time  it  was  set  in  motion.  The  current  passed 
to  a  Serrin’s  lamp,  and  certainly  produced  a  most  brilliant  light. 

In  the  article  on  the  Telegraph,  it  will  be  noticed  that  Sir  Charles  Wheat¬ 
stone  uses  a  magneto-electrical  machine  of  improved  construction,  instead  of 
the  voltaic  battery.  Wheatstone's  exploder  for  military  purposes  generates 
its  electricity  in  the  same  manner.  There  are  many  other  modifications  of 
induced  currents,  such  as  the  experiments  of  Faraday,  “On  the  Induction  of 
a  Current  on  itself,'’  read  before  the  Royal  Society,  1835;  and  Dr.  Henry’s 
(College  of  "New  Jersey,  Princeton;  experiments  ("described  in  1833)  writh  flat 
coils  of  insulated  copper  ribbon  and  helices  of  fine  covered  copper  wire,  by 
which  induced  currents  of  the  third,  fourth,  and  fifth  order  could  be  obtained, 
by  alternately  arranging  the  insulated  copper  ribbons  and  the  helices  of  fine 
wire. 

In  the  “Proceedings  of  the  Royal  Society,”  No.  90,  1867,  Sir  Charles 
Wheatstone  describes  a  most  interesting  series  o  experiments  “On  the  Aug¬ 
mentation  of  the  Power  of  a  Magnet  by  the  reaction  thereon  of  Currents 
induced  by  the  Magnet  itself,”  as  follows  : 

“The  magneto-electric  machines  which  have  been  hitherto  described  arc 
actuated  either  by  a  permanent  magnet  or  by  an  electro-magnet  deriving  its 
power  from  a  rheomotor  placed  in  the  circuit  of  its  coil.  I11  the  present  note, 

I  intend  to  show  that  an  electro-magnet,  if  it  possess  at  the  commencement 
the  slightest  polarity,  may  become  a  powerful  magnet  by  the  gradually  aug¬ 
menting  currents  which  itself  originates. 


4io 


MAGNETISM. 


“  The  following  is  a  description  of  the  form  and  dimensions  of  the  electro¬ 
magnet  I  have  employed.  The  construction,  it  will  be  seen,  is  the  same  as 
that  of  the  electro-magnetic  part  of  Mr.  Wilde’s  machine. 

“  The  core  of  the  electro-magnet  is  t  )rmed  of  a  plate  of  soft  iron,  1 5  in.  in 
length  and  \  an  inch  in  breadth,  bent  at  the  middle  of  its  length  into  a  horse¬ 
shoe  form.  Round  it  is  coiled,  in  the  direction  of  its  breadth,  640  ft.  of  insu¬ 
lated  copper  wire  J-  of  an  inch  in  diameter.  The  armature,  which  is  according 
to  Siemens’s  ingenious  construction,  consists  of  a  rotating  cylinder  of  soft  iron, 

in.  in  length,  grooved  at  two  opposite  sides  so  as  to  allow  the  wire  to  be 
coiled  upon  it  longitudinally;  the  length  of  the  wire  thus  coiled  is  80  ft.,  and 
its  diameter  is  the  same  as  that  of  the  electro-magnet  coil. 

“  When  this  electro-magnet  is  excited  by  any  rheomotor  the  current  from 
which  is  in  a  constant  direction,  during  the  rotation  of  the  armature,  currents 
are  generated  in  its  cell  during  each  semi-revolution,  which  are  alternately  in 
opposite  directions ;  these  alternate  currents  may  be  transmitted  unchanged 
to  another  part  of  the  circuit,  or  by  means  of  a  rheotrope  be  converted  to  the 
same  direction. 

“  If  now,  while  the  circuit  of  the  armature  remains  completed,  the  rheomo¬ 
tor  be  removed  from  the  electro-magnet,  on  causing  the  armature  to  revolve, 
however  rapidly,  it  will  be  found  by  the  interposition  of  a  galvanometer,  or 
any  other  test,  that  but  very  slight  effects  take  place.  Though  these  effects 
become  stronger  in  proportion  to  the  residual  magnetism  left  in  the  electro¬ 
magnet  from  the  previous  action  of  a  current,  they  never  attain  any  consider¬ 
able  amount. 

“  But  if  the  wires  of  the  two  circuits  be  so  joined  as  to  form  a  single  circuit, 
in  which  the  currents  generated  by  the  armature,  after  being  changed  to  the 
same  direction,  act  so  as  to  increase  the  existing  polarity  of  the  electro¬ 
magnet,  very  different  results  will  be  obtained.  The  force  required  to  move 
the  machine  will  be  far  greater,  showing  a  great  increase  of  magnetic  power 
in  the  horse-shoe;  and  the  existence  of  an  energetic  current  in  the  wire  is 
shown  by  its  action  on  a  galvanometer,  by  its  heating  4  in.  of  platinum  wire 
•0067  in  diameter,  by  its  making  a  powerful  electro-magnet,  by  its  decompo¬ 
sing  water,  and  by  other  tests. 

“  The  explanation  of  these  effects  is  as  follows: — The  electro-magnet  always 
retains  a  slight  residual  magnetism, and  is  therefore  in  the  condition  of  a  weak 
permanent  magnet ;  the  motion  of  the  armature  occasions  feeble  currents  in 
alternate  directions  in  the  coils  tnereof,  which,  after  being  reduced  to  the 
same  direction,  pass  into  the  coil  of  the  electro-magnet  in  such  manner  as  to 
increase  the  magnetism  of  the  iron  core ;  the  magnet,  having  thus  received  an 
accession  of  strength,  produces  in  its  turn  more  energetic  currents  in  the  coil 
of  the  armature ;  and  these  alternate  actions  continue  until  a  maximum  is 
attained,  depending  on  the  rapidity  of  the  motion  and  the  capacity  of  the 
electro-magnet. 

“If  the  two  coils  be  connected  in  such  manner  that  the  rectified  current  from 
the  coil  of  the  armature  passes  into  the  coil  of  the  electro-magnet  in  the 
direction  which  would  impart  a  contrary  magnetism  to  the  iron  core,  no  cur-  \ 
rent  is  produced,  and  consequently  there  is  no  augmentation  of  magnetism. 

“  It  is  easy  to  prove  that  the  residual  magnetism  of  the  electro-magnet  is 
the  determining  cause  of  these  powerful  effects.  For  this  purpose  it  is  suffi¬ 
cient  to  pass  a  current  from  a  voltaic  battery,  a  magneto-electric  machine,  or 
any  other  rheomotor,  into  the  coil  of  the  electro-magnet  in  either  direction, 


IVHEA  TS  TONE'S  EX  PER  I M ENTS. 


41 1 


and  it  will  invariably  be  found  that  the  direction  of  the  current,  however 
powerful  it  may  eventually  become,  is  in  accordance  with  the  polarity  of  the 
magnetism  impressed  on  the  iron  core. 

“  If,  instead  of  the  currents  in  the  coil  of  the  rotating  armature  being  re¬ 
duced  to  the  same  un  form  direction,  they  retain  their  alternations,  no  effects, 
or  at  most  very  small  differential  ones,  are  produced,  as  no  accumulation  of 
magnetism  then  takes  place. 

“  I  will  now  call  attention  to  the  fact  that  stronger  effects  are  produced  at 
the  first  moment  of  completing  the  combined  circuit  than  afterwards.  The 
machine  having  been  put  in  motion,  at  the  first  moment  of  completing  the 
circuit  4  in.  of  platina  wire  were  made  red  hot ;  but  immediately  afterwards 
the  glow  disappeared,  and  only  about  one  inch  of  the  wire  could  be  perma¬ 
nently  kept  at  a  red  neat.  This  diminution  of  effect  was  accompanied  by  a 
great  increase  of  the  resistance  of  the  machine.  The  cause  of  the  momentary 
strong  effect  was,  that  the  machine  from  its  acquired  momentum  continued 
its  motion  for  a  few  seconds,  though  it  required  a  stronger  force  than  could 
be  applied  to  maintain  that  motion.  Each  time  the  circuit  is  broken  and  re¬ 
completed,  the  same  effect  recurs. 

“On  bringing  the  primary  coil  of  an  inductorium  (Ruhmkorff’s  coil)  into 
the  circuit  formed  by  connecting  the  coils  of  the  electro-magnet  and  rotating 
armature,  no  spark  occurs  in  the  secondary  coil.  On  account  of  the  great 
resistance  of  the  circuit,  which  now  also  includes  the  primary  coil  of  the  in- 
ductcrium,  the  current  is  not  in  sufficient  quantity  to  produce  any  noticeable 
inductive  effect. 

“A  very  remarkable  increase  of  all  the  effects,  accompanied  by  a  diminu¬ 
tion  in  the  resistance  of  the  machine,  is  observed  when  a  cross  wire  is  placed 
so  as  to  divert  a  great  portion  of  the  current  from  the  electro-magnet.  The 
four  inches  of  platinum  wire,  instead  of  flashing  into  redness  and  then  dis¬ 
appearing,  remains  permanently  ignited.  The  inductorium,  which  before  gave 
no  spark,  now  gave  one  a  quarter  f  an  inch  in  length  ;  water  was  more  abun 
dantly  decomposed;  and  all  the  other  effects  were  similarly  increased. 

“  I  account  for  this  augmentation  of  the  effects  in  the  following  way: 

“  Though  so  much  of  the  current  is  diverted  from  the  electro-magnet  by 
the  cross  wire,  the  magnetic  effect  still  continues  to  accumulate,  though  not 
to  so  high  a  degree;  but  the  current  generated  by  the  armature,  passing 
through  the  short  circuit  formed  by  the  armature  branch  and  cross  wire, 
experiences  a  far  less  resistance  than  ii  it  naa  passed  through  the  armature 
and  electric-magnet  branches;  and  though  the  electromotive  force  is  less,  the 
resistance  having  been  rendered  less  in  a  much  greater  proportion,  the  result¬ 
ant  effect  is  greater. 

“  I  must  observe  that  a  certain  amount  of  resistance  in  the  cross  wire  is 
necessary  to  produce  the  maximum  effect.  If  the  resistance  be  too  small,  the 
electro-magnet  does  not  acquire  sufficient  magnetism  ;  and  if  it  be  too  great, 
though  the  magnetism  becomes  stronger,  the  increase  of  resistance  more  than 
counterbalances  its  efflct. 

“  But  the  effects  already  described  are  far  inferior  to  those  obtained  by 
causing  them  to  take  place  in  the  cross  wire  itself.  With  the  same  applica¬ 
tion  of  force,  7  in.  of  platinum  wire  were  made  red  hot,  and  sparks  were 
elicited  in  the  inductorium  i\  in.  in  length. 

“The  force  of  two  men  was  employed  in  these,  as  well  as  in  the  other 
experiments.  When  the  interrupter  of  the  primary  coil  was  fixed,  the  machine 


412 


MAGNETISM. 


was  much  easier  to  move  than  when  it  acted.  For  when  the  interrupter  acted, 
at  each  moment  of  interruption  the  cross  wire  being,  as  it  were,  removed,  the 
whole  of  the  current  passed  through  the  electro-magnet,  and  consequently  a 
greater  amount  of  magnetic  energy  was  excited,  while  in  the  intervals  during 
which  the  cross  wire  was  complete  the  current  passed  mainly  through  the 
primary  coil. 

“  The  effects  are  much  less  influenced  by  a  resistance  in  the  electro-magnet 
branch  than  in  either  of  the  other  branches. 

“  To  reduce  the  length  of  the  spark  in  the  inductor  ium  (the  primary  coil  of 
which  was  placed  in  the  cross  wire)  to  jj-  of  an  inch,  it  required  the  resistance 
of  sl  in.  °f  the  fine  platinum  wire  in  the  cross  wire,  5  in.  in  the  armature 
branch,  and  4  ft.  ;n  the  electro-magnet  branch. 

‘•When  there  was  no  extraresistance  in  either  of  the  branches,  the  length  of 
the  cross  wire  being  only  about  a  few  feet,  the  intensity  of  the  current  in  the 
electro-magnet  branch,  compared  with  that  in  the  cross  wire,  was  as  1:60; 
and  when  the  resistance  of  the  primary  coil  of  the  inductorium  was  interposed 
in  the  cross  wire,  the  relative  intensities  were  as  1  142. 

“  In  conclusion,  1  will  mention  that  there  is  an  evident  analogy  between  the 
augmentation  of  the  power  of  a  weak  magnet  by  means  of  an  inductive  action 
produced  by  itself,  and  that  accumulation  of  power  shown  in  the  static  elec¬ 
tric  machines  of  Holtz  and  others,  which  have  recently  excited  considerable 
attention,  in  which  a  very  small  quantity  of  electricity  directly  excited  is,  by  a 
series  of  inductive  actions,  augmented  so  as  to  equal,  and  even  exceed,  the 
effects  of  the  most  powerful  machines  of  the  ordinary  construction.” 

Mr.  Wilde’s  machine  has  been  fully  described  in  all  the  illustrated  scientific 
papers,  such  as  “  Tiie  Engineer”  and  “The  Mechanic’s  Magazine.”  The 
writer,  therefore,  proposes  to  give  drawings  of  Mr.  Ladd’s  improved  magneto¬ 
electric  machine,  which  he  thus  describes  in  the  “Transactions  of  the  Royal 
Society,”  No.  91,  1867: 

“  In  June,  1864, 1  received  from  Mr.  Wilde  a  small  magneto-electric  machine, 
consisting  of  a  Siemens’s  armature  and  six  magnets.  This  I  endeavoured  to 
improve  upon,  my  object  being  to  get  a  cheap  machine  for  blasting  with  Abel’s 
fusees.  This  was  done  by  making  one  of  circular  magnets,  and  a  Siemens’s 
armature  revolving  directly  between  the  poles,  the  armature  forming  part  of 
the  circle;  with  this  I  could  send  a  very  considerable  power  into  an  electro¬ 
magnet,  &c.  It  was  then  suggested  to  me,  bv  my  assistant,  that  if  the  arma¬ 
ture  had  two  wires  instead  of  one,  the  current  from  one  being  sent  through  a 
wire  surrounding  the  magnets,  their  power  would  be  augmented,  and  a  con¬ 
siderable  current  might  be  obtained  from  the  other  wire  available  for  external 
work ;  or  there  might  be  two  armatures — one  to  exalt  the  power  of  the  magnets, 
and  the  other  made  available  for  blasting  or  other  purposes.  Want  ot  time 
prevented  me  carrying  this  out  until  now;  but  since  the  interesting  papers  of 
C.  W.  Siemens,  F.R.S.,  and  Professor  Wheatstone,  F.R.S.,  were  read  last 
month,  I  have  carried  out  the  idea  as  follows:— Two  bars  of  soft  iron,  mea¬ 
suring  in.  X2|  in.  X1.  in.,  are  each  wound,  round  the  centre  portions,  with 
about  thirty  yards  of  No.  10  copper  wire ;  and  shoes  of  soft  iron  are  so  attached 
at  each  end,  that  when  the  bars  are  placed  one  above  the  other  there  will  be  a 
space  left  between  the  opposite  shoes,  in  which  a  Siemens’s  armature  can  rotate: 
on  each  of  the  armatures  is  wound  about  ten  yards  of  No.  14  copper  wire, 
cotton-covered.  The  current  generated  in  one  of  the  armatures  is  always  in 
connexion  with  the  electro-magnets;  and  the  current  from  the  second  arma- 


MA  GNE  70-ELECTRICITY. 


4i3 


turc.  being  perfectly  free,  can  be  used  for  any  purpose  for  which  it  may  be 
required.  The  machine  is  altogether  rudely  constructed,  and  is  only  intended 
to  illustrate  the  principle  ;  but  with  this  small  machine  three  inches  of  platinum 
wire  01  can  be  made  incandescent.” 

Mr.  Ladd  calls  this  machine  the  “  Dynamo-Magnetic  Machine”  (Fig.  360). 


Fig.  360. 


This  machine  was  awarded  a  silver  medal  at  the  Paris  Exhibition,  1867. 
Another  form  of  the  apparatus  (Fig.  361),  also  constructed  by  Mr.  Ladd,  is 
that  in  which  the  two  armatures  are  combined  in  one,  and  the  coils  are  wound 
at  right  angles  to  each  other. 

The  results  obtained  are  simply  regulated  by  the  amount  of  mechanical 
force  used  to  rotate  the  armatures  ;  and  thus  indirectly  coal,  used  as  a  means 
of  exciting  electricity,  is  made  to  generate  steam,  which  produces  force  in 
the  steam  engine,  and  this  ultimately  turns  the  dynamo-magnetic  machine  ; 
and  thus  indirectly  coal  generates  an  electric  current,  by  which  the  electric 
light  is  obtained. 

These  machines  have  been  surpassed  by  one  invented  by  Monsieur  Gramme, 
and  now  made  by  the  Gramme  Magneto-Electric  Company,  of  52  Rue  Saint 
George,  Paris.  The  writer  has  seen  one  in  useful  action  in  the  splendid 
physical  laboratory  of  Mr.  Spottiswoode,  and  its  power  most  usefully  applied 


4T4 


MAGNETISM. 


Fig.  361. 


either  for  electrotyping,  electric  light,  and  many  other  industrial  applications, 
especially  for  experimental  researches.  The  yacht  “  Livadia,”  of  the  Emperor 
of  Kussia,  has  been  furnished  with  a  ‘•Gramme”  machine  for  the  production 
of  an  intense  electric  light.  The  limits  of  this  work  forbid  the  lengthened 
description  required  to  explain  the  admirable  principle  of  this  machine,  which, 
starting  with  a  minimum  “  potential,”  works  up  by  motion  to  great  energy. 

A  convenient  little  magneto-electrical  machine  is  made  by  Mr.  Browning, 
for  the  purpose  of  giving  shocks  and  for  medical  use.  (Fig.  362.) 

Directions  for  using  the  Instrument. — Take  the  hollow  conductors  A  B  off 
from  the  large  studs  on  which  they  are  placed  ;  uncoil  their  metallic  cords 
which  are  wound  upon  them,  and  insert  the  pins  which  are  attached  to  the 
ends  of  these  cords  into  the  small  holes  which  will  be  found  in  two  upright 
brass  studs  at  the  back  of  the  stand  of  the  machine,  marked  C  D  in  the  dia¬ 
gram  ;  then  upon  holding  the  hollow  conductors,  one  in  each  hand,  and  turn¬ 
ing  the  handle  of  the  machine  quickly,  a  strong  electrical  current  will  be 
felt. 

A  horizontal  stud  in  front  of  the  machine,  projecting  beyond  the  frame, 
serves  to  move  an  iron  feeder  before  the  ends  of  the  large  circular  magnet. 
By  shifting  this  feeder,  the  strength  of  the  current  given  out  by  the  machine 
can  be  regulated  within  any  desirable  limit.  When  the  feeder  is  lifted  up  in 
front  of  the  magnet,  the  current  will  be  very  feeble  ;  when  it  is  withdrawn 
quite  below  the  magnet,  it  will  be  very  intense. 

Two  brass  springs  project  from  the  brass  studs  C  D  ;  these  springs  should 


MA  GNE  TO- EL  ECTRLCITY. 


4i5 


rest  on  the  edge  of  a  small  wheel  of  ebonite  and  brass,  known  as  a  commu¬ 
tator.  It  sometimes  hnnnens  that,  from  rough  usage  in  carriage,  these  springs 
are  bent,  so  that  they  no  longer  touch  the  edge  of  tiie  wheel  ;  in  this  case  the 

current  becomes  greatly  weakened,  or 
altogether  ceases  ;  but  the  machine  can 
be  easily  set  right  by  carefully  bending 
down  the  springs  so  that  they  again 
rest  upon  the  edge  of  the  wheel. 

We  now  come  to  the  last  of  the  in¬ 
duction  machines,  sometimes  called  the 
induction  coil,  the  inductorium,  &c.  In 
1851,  M.  Ruhmkorff.  a  most  clever  in¬ 
strument  maker  in  Paris,  made  a  coil 
which  produced  in  the  scientific  world 
of  Paris  and  London  a  profound  sen¬ 
sation  of  surprise  and  delight  at  the 
beautiful  light  effects  obtainable. 

Mr.  Heartier,  of  Plymouth,  and  Mr. 
Bentley,  subsequently  made  coils  of 
great  power  ;  but  to  Mr.  Ladd  is  due 
the  merit  of  constructing  a  serviceable 
apparatus  which  v’ould  always  produce  the  most  reliable  results.  A  very 
large  coil,  having  a  secondary  coil  of  seven  miles  of  wire,  has  long  been  used 
at  the  Polytechnic.  It  consists  of  the  usual  primary  coil,  wound  round  a 
faggot  of  iron  wires;  around  this  is  the  secondary  coil, of  the  required  number 
of  miles  in  length.  The  condenser,  composed  of  alternate  sheets  of  tinfoil 
and  well  dried  and  varnished  paper,  is  placed  under  the  coil,  and,  by  making 
and  breaking  contact  with  the  primary  by  a  convenient  “  contact-breaker,” 
an  enormous  current  is  induced  in  the  secondary,  which  produces  the  most 
brihiant  results. 


Fig.  362. — Browning’s  Magneto- 
Electrical  Machine. 


Fig.  363. — Pliicket  's  Tube. 

A  Leyden  jar  or  Lev  den  plate  may  be  incessantly  charged  and  disenarged 
with  a  continuous  roar.  Paper  is  immediately  set  on  fire  when  held  between 
the  poies.  Tubes  of  glass  are  filled  with  various  gases  or  liquids,  or  rather 
not  filled  according  to  the  ordinary  acceptation  of  the  term,  because  they  are 
vacua ,  the  last  gas  which  has  been  permitted  to  enter  the  tube  alone  repre¬ 
senting  the  attenuated  atmosphere  through  which  the  electric  current  passes. 

The  reader  is  referred  to  l)r.  Noad’s  little  book,  entitled  “The  Inductorium,” 
and  published  by  Churchill  for  Mr.  Ladd,  for  all  the  minute  details  connected 
with  the  primary  coil,  the  secondary,  the  condenser,  and  the  thousand-and- 


4t5  MAGNETISM. 


jne  experiments  which,  like  the  “Arabian  Nights’  Entertainments,”  crowd 
upon  the  student,  but  which  may  all  be  performed  with  the  apparatus  described. 

Amongst  the  most  interesting  experiments,  that  of  Pliicker  deserves  especial 
lotice. 

“Two  aluminium  rings  are  hermetically  sealed  into  a  glass  tube,  4  or  5  in. 
long  and  about  i|  in.  in  diameter;  the  air  in  the  tube  is  then  exhausted  as 
perfectly  as  possible.  On  passing  the  discharge  from  the  induction  coil  between 
the  two  rings,  the  tube  becomes  filled  with  a  beautiful  pale  blue  light. 


FlG.  364. — Pliicker' s  Tube  with  Aluminium  Wires. 

“  If  the  small  ring  be  made  negative,  and  the  tube  placed  between  the  poles 
of  an  electro-magnet,  the  moment  the  latter  is  excited  the  light  arranges  itself 
in  the  form  of  a  broad  arc  between  the  rings. 


Fig.  365. — Gassiot’s  Cascade , 

1  he  current  passing  into  and  out  of  a  glass  vessel  placed  in  a  vacuum 

“  On  rendering  the  electro-magnet  passive,  the  arc  disappears,  the  light  in 
the  tube  re-assuming  its  different  character  ;  but,  on  re-exciting  the  magnet, 


MA  GNE  TO-ELECTR/CITV. 


4i7 


the  arc  re-appears.  If,  instead  of  two  rings,  the  terminals  in  the  tube  are  two 
aluminium  wires,  as  shown  in  Fig.  364,  the  long  wire  being  made  positive  and 
the  short  wire  negative,  the  arc  produced  is  very  broad  and  brilliant.” 

It  must  be  apparent  from  the  preceding  figures  that  the  stratification  notice¬ 
able  in  all  experiments  of  this  type  is  a  special  object  of  interest,  to  which  M. 
Gassiot,  the  generous  and  large-hearted  friend  of  science,  has  paid  particular 
attention. 

Speaking  of  Geissler’s  (of  Bonn)  tubes, — one  of  the  prettiest  arrangements 
the  writer  has  seen  is  that  of  Mr.  Apps,  and  shown  in  the  next  figure. 


Fig.  366. — Front  View  of  Geissler's  Tubes ,  arranged  on  a  disc  of  blackened 

Mahogany. 


The  back  view  exhibits  the  use  ol  the  electro-magnetic  engine  for  rotating 
or  reversing  the  disc.  (Fig.  367.) 

The  electro-magnetic  engine,  in  a  convenient  and  handsome  form,  well 
adapted  to  rotate  the  vacuum  tubes,  is  attached  to  the  black  polished  disc,  and 
arranged  so  as  to  turn  in  either  direction :  the  speed  can  be  easily  regulated. 
The  discharge  from  the  coil  passes  through  the  entire  series  of  tubes. 

Amongst  the  remarkable  effects  produced  by  the  induction  coil,  there  are 
none  more  interesting  than  the  generation  of  ozone  by  the  “  ozone  tube,”  which 
is  thus  described  by  Dr.  Noad,  and  made  by  Mr.  Ladd.  (Fig.  368.) 

It  consists  of  a  glass  tube,  about  the  size  of  an  ordinary  test  tube,  coated 
with  tinfoil  or,  still  better,  silvered,  and  enclosed  in  an  outer  tube  lined  out¬ 
side  with  tinfoil.  The  two  tubes  are  sealed  together  at  the  neck  of  the  outer 

•  27 


418 


MAGNETISM. 


Fig.  367. 


through  by  means  of  a  bladder  or  india-rubber  ba 
aspirator. 


one,  and  so  adjusted  that 
the  space  between  them 
shall  be  as  narrow  as  pos¬ 
sible. 

At  the  projecting  end  of 
the  inner  tube  is  a  brass 
button,  which  is  connected 
by  a  spring  with  one  of  the 
binding-screws  on  the  frame 
of  the  apparatus,  which 
screw  is  to  be  connected 
with  one  of  the  terminals  of 
the  secondary  coil  of  an  in- 
ductorium,  and  the  other 
with  another  binding-screw 
in  metallic  communication 
with  the  coating  of  the  ex¬ 
terior  tube. 

The  apparatus  is,  in  fact, 
a  sort  of  slit  Leyden  jar; 
and  air  or  oxygen,  admitted 
through  the  lateral  tube,  be¬ 
comes  during  its  passage 
through  the  apparatus  pow¬ 
erfully  ozonized. 

The  air  may  be  driven 
g,  or  drawn  through  with  an 


Fig.  368.^- 'The  Ozone-Tube. 


Mr.  Edward  Beanes,  who  has  already  done  so  much  in  improving  certain 
processes  required  in  the  manufacture  of  sugar,  has  patented  the  application 
of  apparatus  for  generating  ozone  and  bleaching  syrup,  and,  although  there 
appears  to  be  some  difficulty  in  obtaining  enough  ozone  for  this  purpose,  the 
experiments  hitherto  tried  are  very  promising. 

1  he  writer  abstains  from  saying  anything  about  a  new  gigantic  coil,  building 
for  the  Polytechnic  by  Mr.  Apps.  Like  David  with  his  armour,  he  has  not 
proved  it :  had  he  done  so,  this  article  would  have  contained  an  account  ol 
the  Mammoth  Induction  Coil. 


THERMO-ELECTRICITY. 


419 


THERMO-ELECTRICITY. 


Electricity  produces  magnetism,  heat,  light,  mechanical  and  chemical  effects. 
It  is  not  opposed  to  the  harmony  of  created  forces  that  heat  should  produce 
electricity. 


Fig.  369. — Marcus's  Thermo-Electric 
Battery ,  made  by  Mr.  Ladd. 


3 


1 

1"  "  " 

! - r 

r  — 

CD 

Fig.  370. 


The  above  battery  (Fig.  369)  consists  of  thirty-six  elements;  the  negative 
bars,  which  are  6  in.  long,  being  composed  of  12  parts  of  antimony,  5  of  zinc, 
and  1  of  bismuth;  and  the  positive  bars,  which  are  7  in.  long,  of  copper  10  parts, 
zinc  6  parts,  and  nickel  6  parts.  The  bars  are  ranged  on  a  frame  in  the  slanting 
position  shown  in  the  figure,  and  were  facetiously  referred  to  by  a  writer  in 
“  Punch  ”  as  a  “  chestnut  roaster,”  the  positive  bar  of  the  first  pair  being  metal¬ 
lically  connected  with  the  negative  of  the  second,  and  the  two  extreme  bars 
connected  with  binding-screws  which  form  the  terminals  of  the  battery.  The 
upper  ends  of  the  bars  are  heated  by  a  series  of  Bunsen’s  burners,  the  flames  of 
which  can  be  easily  regulated. 

This  battery  at  the  Polytechnic,  under  the  charge  of  Mr.  J.  L.  King,  decom¬ 
posed  water,  of  course  very  feebly;  it  gave  small  sparks  between  iron  points 
without  the  assistance  of  a  coil,  and  enabled  an  electro-magnet  to  support  a 
Considerable  weight,  and,  when  connected  with  an  induction  coil,  gave  sparks 
which  were  very  marked  in  their  character  and  length. 

We  have  now  to  ask  how  this  apparatus,  in  which  heat  takes  the  place  of 
friction,  chemical  action,  or  magnetism,  elicits  electric  force. 

Seebeck’s  apparatus,  a  rectangular  figure,  made  ot  bismuth  and  antimony, 
with  an  astatic  magnetic  needle  supported  inside,  well  exhibits  the  thermo¬ 
electric  action ;  and,  directly  one  of  the  angles  is  gently  heated  by  a  spirit 
flame,  the  needle,  like  that  of  the  galvanometer  with  the  voltaic  circuit,  is 
deflected.  (Fig.  370.) 

Pouillct’s  thermo-electric  apparatus  (made  by  Elliott),  and  already  figured 
in  Wheatstone’s  paper  on  the  Rheostat  (p.  333),  consisting  of  a  short  cylindrical 
bar  of  bismuth,  bent  twice  at  right  angles,  with  soldered  copper  wires  attached 
to  the  ends,  communicating  with  an  ingenious  contrivance  on  the  stand  for 

27 — 2 


420 


MAGNETISM. 


Fig.  371. — Pouillet  Thermo-Electric  Circle. 

completing  the  electric  circuit  in  any  direction,  is  another  and  most  perfect 
arrangement  for  showing  currents  of  electricity  obtainable  by  the  exciter, 
“heat.”  (Fig.  371.) 

On  the  second  or  third  page  of  this  work,  in  the  article  on  Light,  Melloni's 
small  and  compact  composite  “  thermo-electric  pile  ”  is  specially  alluded  to. 

When  the  writer  was  a  student,  thirty  years  ago,  he  well  remembers  trying 
experiments  with  this  beautiful  contrivance  for  showing  minute  disturbances 
of  heat;  and,  at  that  time,  it  had  the  reputation  of  being  delicate  enough  to 
show  the  heat  of  the  body  of  a  “  fly  or  a  blue-bottle.”  Exaggeration  apart,  its 


Fig.  372.  -Melloni's  Thermo-Electric  Pile  or  Battery. 

power  to  show  the  slightest  heat-wave  disturbance  has  never  been  equalled  by 
any  other  apparatus.  It  consists  of  a  series  of  pairs  of  very  slender  bars  cf 
antimony  and  bismuth  soldered  alternately  together,  and  arranged  parallel 
side  by  side,  so  that  all  the  soldered  pairs  are  at  one  end,  and  all  the  solders 
not  pairs  at  the  other.  This  apparatus,  mounted  in  a  brass  tube  and  placed 
on  a  stand,  is  now  the  special  attendant  at  all  lectures  in  which  the  dynamical 
theory  of  heat  is  taught.  (Fig.  372.) 

The  late  Mr.  Francis  Watkins,  the  predecessor  of  the  Messrs.  Elliott,  paid 
particular  attention  to  this  subject,  and  constructed  a  “  Thermo-Electric  Com- 
binator.”  Eighteen  pairs  of  bismuth  and  antimony,  united  alternately  by 


THERMO-ELECTRICITY. 


421 


Fro.  373. —  Van  der  Voort's  Thermo-Electric  Battery. 


solder  top  and  bottom,  and  fixed  in  a  mahogany  box  by  plaster  of  paris, 
leave  the  two  extremities  to  be  acted  upon,  the  om  by  heat  and  heated  iron 
or  boiling  oil,  and  the  other  by  cold — some  ice  or  ?.  freezing  mixture.  All  the 
common  effects  of  an  electric  current,  such  as  the  spark,  <Scc.,  can  be  shown 
with  this  contrivance. 

Thus  the  correlation  of  forces  is  complete,  and  Light,  Heat,  Electricity,  and 
Magnetism  resolve  themselves  into  each  oilier,  and  represent  probably  a 
series  ot  waves,  every  one  of  which  is  different  from  the  other  in  the  phases 
of  its  vibrations  and  resultant  form. 

At  page  321,  Fig.  268,  the  burning  or  oxidation  of  carbon  is  shown  to  be  a 
direct  source  of  electric  power.  In  the  following  arrangement,  invented  and 
patented  by  C.  and  L.  Wray,  the  combustion  of  gas  or  coke  is  made  indirectly 
to  give  a  good  and  useful  current  of  electricity. 

C.  and  L.  Wray’s  Patent  Thermo-Electric  Pile. 

This  pile  differs  in  many  respects  from  any  that  have  preceded  it — notably 
in  the  heating  arrangements,  in  the  building  up  of  the  couples,  and  in  the  con¬ 
struction  of  the  bars  themselves. 

The  accompanying  drawings  give  a  clear  idea  of  the  novel  features  of  this 
battery.  Fig.  N  is  a  vertical  section  of  a  pile  of  225  couples,  built  in  three 
sections  of  75  couples  each. 

It  will  be  seen  that  the  thermo-electric  bars  are  arranged  round  and  abut 
against  the  outside  of  the  heating-chamber,  which  is  formed  of  an  earthen¬ 
ware  tube  or  cylinder,  a.  In  the  centre  of  this  tube  a  Bunsen  or  other  suitable 
burner  is  placed,  b,  inside  which  is  a  cylinder  of  fine  wire  gauze — the  object  of 
this  latter  being  to  prevent  the  explosions  which  occur  on  lighting  and  turn¬ 
ing  off  the  gas,  especially  when  large  burners  are  employed,  and  to  cause  the 
gas  to  be  more  equally  distributed  through  the  holes  in  the  burner. 

By  building  up  the  bars  against  the  walls  of  the  heating-chamber,  several 
important  points  are  gained:  1.  The  metals  of  which  the  couples  are  com¬ 
posed  are  protected  from  the  injurious  action  of  the  flame  and  products  of 
combustion,  and  also  from  the  action  of  damp  and  air.  2.  1  he  tube  is  of  such 
a  thickness  as  to  prevent  an  injurious  amount  of  heat  passing  through  to  the 
bars.  3.  The  tube  acts  as  a  diffuser  or  carrier  of  the  heat,  thus  causing  the 
various  zones  of  bars  to  be  uniformly  heated.  And,  lastly,  it  prevents  the 
bars  from  being  heated  and  cooled  too  rapidly. 

The  admission  of  air  for  combustion  to  the  annular  space  can  he  regulated 


422 


MAGNETISM. 


Fig.  M. — C.  and  L.  Wray's  Thermo  Pile. 

a,  the  earthenware  tube  and  insulating  annular  discs  ;  b,  apparatus  complete ;  c,  one  of  the  thermo¬ 
electric  couples. 


with  great  nicety  by  means  of  the  arrangement  shown  at  the  lower  end  of  the 
heating-chamber,  c  c  are  openings,  which  can  be  more  or  less  closed  by  the 


K  K 


Fig.  n. 


disc,  d,  which  screws  up  and  down  the  pipe,  e;  whilst  the  draught  is  further 
regulated  by  means  of  a  perforated  earthenware  cap,  which  fits  over  the  top 


THERMO-ELEC  TRICITY 


423 


of  the  cylinder  ;  fff  are  the  thermo-electric  couples  ;  g  g  are  the  insulating 
annular  discs,  between  which  the  bars  or  couples  are  placed  ;  and  g'  g'  g' 
are  blocks  which  support  the  weight  of  the  superincumbent  layers  of  bars, 


and  through  these  blocks  run  binding-rods,  h,  h.  Fig.  o  shows  this  f.ame- 
work  more  clearly. 

The  advantage  claimed  for  this  mode  of  construction  is  that  the  bars  are 
relieved  of  all  pressure,  and  can  with  greater  facility  be  built  up  in  sections  ; 
and  the  whole  pile  is  rendered  firmer  and  stronger. 


Fig.  r. 


The  pile  is  mounted  on  an  iron  framework,  which  is  bound  or  held  together 
by  the  rods,  hl  hl.  The  bars,  or  couples,  may  be  made  of  any  of  the  known 
thermo-electric  metals.  When  an  easily  fusible  metal  analagous  to  that  used 
by  Rollman,  Marcus,  Baker,  Clamond,  and  others,  is  employed  for  the  nega¬ 
tive  bar,  the  positive  metal  is  cut  into  the  shape  of  a  dovetail  at  the  heated 
end,  and  at  the  cool  end,  in  addition  to  the  dovetail,  there  is  an  elongation  or 


424 


MAGNETISM. 


tongue.  Through  both  dovetails  one  or  more  perforations  are  made.  Figs. 
P  and  Q  represent  longitudinal  vertical,  and  longitudinal  horizontal  sections 
of  a  bar  ;  f  is  the  negative  alloy,  i  i  the  positive  metal,  i1  the  elongation  or 
tongue,  i2,  the  outer  positive.  1  he  positives  are  fixed  in  the  mould,  and  the 
negative  bars  are  cast  upon  them  under  pressure.  Figs.  R  and  S  represent  a 
pile  adapted  for  burning  coke,  or  other  solid  fuel. 

In  Fig.  s,  A  is  the  fire-chamber,  and  a  a  the  wall  or  cylinder  of  refrac¬ 
tory  clay,  around  and  touching  which  the  bars,//,  are  arranged  ;  g  g  are  the 
discs,  and//  the  blocks  with  the  tie-rods  through  them  ;  j  and  /are  doors 
for  obtaining  access  to  the  fire  ;  these,  as  shown  in  Fig.  R,  extend  the  whole 
height  of  the  pile  ;  k  k  k  are  the  fire-bars  ;  l  l  are  vertical  fire-bars,  which 
are  movable  to  allow  of  stoking  and  the  ready  withdrawal  of  clinkers  ;  in  is 
the  cover,  or  top  of  chamber,  through  which  the  fire  is  supplied  with  fuel ;  the 
products  of  combustion  pass  up  the  chimney,  n.  The  ash-pit  is  provided 
with  doors,  o  o,  in  which  are  sliding  draught  regulators. 

Messrs.  Wray  sum  up  advantages  of  their  new  thermo-pile  as  follows  : 

“The  improvements  comprised  in  our  new  patent  are  threefold  :  i.  A  new 
alloy,  of  which  we  form  our  negative  bars,  consisting  of  antimony,  iron,  and 
zinc.  This  is  stronger  and  much  less  fusible  than  the  antimony  and  zinc 
commonly  employed.  2.  The  mode  of  casting  thin  bars,  so  that  they  maybe 
perfectly  sound  and  also  free  from  crystalline  structure.  When  the  bars  are 
cast  in  the  usual  way — i.e.,  in  metal  moulds,  either  heated  or  otherwise — the 
bars  suffer  from  two  defects,  viz.,  cracks,  and  in  the  case  of  hot  moulds,  a 
defective  connection  between  the  positive  and  negative  metals.  We  get  over 
both  these  dangers  by  using  a  peculiar  mould  made  of  earthenware.  The 
metal  when  poured  into  these  moulds  cools  very  slowly  and  equally  ;  there  is 
no  chilling  of  the  surfaces,  and  consequently  no  cracks  ;  and  as  the  tinned 
iron  positives  are  not  heated  (as  the  mould  in  which  they  are  placed  is  used 
cool),  a  good  metallic  connection  is  insured  3.  Wc  build  our  piles  so  that  the 
bars  are  entirely  embedded  in  daywork,  nothing  being  exposed  except  the 
connection  at  the  outer  or  cool  end.  This  plan  has  many  advantages,  amongst 
which  are  the  following:  the  bars  are  protected  from  all  external  injury;  they 
heat  and  cool  (on  lighting  and  turning  out  the  pile)  more  slowly  and  equally, 
and  their  durability  is  increased.  Small  telegraphic  bars  are  not  thus  en¬ 
cased,  but  all  ordinary-sized  ones  are.  There  is  very  little,  if  any,  loss  of 
power  in  building  them  this  way,  as  the  clay  in  which  they  are  embedded  is 
a  very  bad  conductor  of  heat.” 


WHEA  TSTONE  'S  TELEGRAPHS. 


425 


WHEATSTONE’S  TELEGRAPHS. 

The  limits  of  this  article  will  not  permit  of  any  lengthened  history  of  all 
the  clever  inventions  either  proposed  or  carried  out  by  the  various  scientific 
men  who  have  contributed  to  our  knowledge  of  the  science  of  telegraphy. 

Whatever  amount  of  credit  may  be  accorded  to  others,  there  can  be  but  one 
opinion  respecting  the  merits  of  the  late  Sir  Charles  Wheatstone,  whose  portrait 
graces  the  head  of  this  chapter  Foreigners  are  usually  very  frank  and  honest 
in  their  expression  of  the  amount  of  merit  due  to  their  contemporaries  in  other 


426 


MAGNETISM. 


countries.  The  jury  of  the  French  Exhibition  of  1855  thus  report  upon 
Wheatstone : 

“  La  transmission  de  l’electricite  entre  les  pays  sdpares  par  la  mer  n’a  pu 
s’effectuer  qu’au  moyen  de  cables  particulars  unissant  entre  elles  les  stations 
telegraphiques.  Mais  combien  de  travaux  n’a-t-il  pas  fallu  pour  atteindre  ce 
but;  et  meme  maintenant  que  la  question  est  resolue,on  ne  peut  sans  admiration 
penser  que  la  transmission  des  depeches  telegraphiques  est  aussi  facile  h  l’aide 
des  cables  sous-marins  qu’au  moyen  des  fils  isoles  et  tendus  dans  Fair.  C’est 
par  l’emploi  de  ces  cables  que  l’on  a  pu  mettre  en  relation  telegraphique  la 
France  et  l’Angleterre,  la  Crimee  et  les  provinces  Danubiennes,  les  pays  enfin 
dans  lesquels  ces  principes  ont  ete  appliques,  et  peut-etre  bientot  l’Europe  et 
l’Amerique.  Le  Jury  a  vote  une  mention  tres-honorable  pour  M.  Wheatstone 
(Royaume  Uni),  membre  du  Jury  de  la  IX'  classe,  pour  avoir  congu  l’idee  pre¬ 
miere  et  pour  avoir  propose,  en  1840,  un  moyen  de  resoudre  la  question;  il 
accorde  la  meme  distinction  a  M.  Brett  (Royaume  Uni),  sous  la  direction 
duquel  a  ete  place  un  conducteur  au  travers  de  la  Manche,  entre  Douvres  et 
Calais,  et  qui  a  montre  ainsi  que  le  succes  etait  possible-.-,  Le  Jury  decerne 
egalement  une  mention  tres-honorable  a  M.  Crampton  (Royaume  Uni), 
membre  du  Jury  de  la  Ve  classe,  auquel  revient  l’honneur  d’avoir  realise  cette 
immense  application,  en  unissant  definitivement,  en  1851,  par  un  cable  sous- 
marin,  la  France  et  l’Angleterre.” 

Another  very  distinguished  foreigner,  A.  De  la  Rive,  thus  speaks  of  Wheat¬ 
stone  in  his  “Treatise  on  Electricity:” 

“The  philosopher  who  was  the  first  to  contribute  by  his  labours,  as  inge¬ 
nious  as  they  were  persevering,  in  giving  to  electric  telegraphy  the  practical 
character  that  it  now  possesses  is,  without  any  doubt,  Mr.  Wheatstone.  This 
illustrious  philosopher  was  led  to  this  beautiful  result  by  the  researches  that 
he  had  made  in  1834  upon  the  velocity  of  electricity — researches  in  which  he 
had  employed  insulated  wires  of  several  miles  in  length,  and  which  had 
demonstrated  to  him  the  possibility  of  making  voltaic  and  magneto-electric 
currents  to  pass  through  circuits  of  this  length.” 

The  following  is  the  order  of  the  inventions  made  by  Sir  Charles  Wheat¬ 
stone: 

The  5-needle  telegraph,  1837. 

The  alphabet-dial  telegraph,  1840. 

The  type-printing  telegraph,  1841. 

The  new  magnetic  alphabetic-dial  telegraph,  1858-60. 

The  fast-speed  automatic  telegraph,  1858 — 1867. 

Sir  Charles  Wheatstone,  in  addition  to  the  other  honours  he  has  lately  re¬ 
ceived,  has  just  been  elected  to  replace  Faraday  as  one  of  the  twelve  corre¬ 
sponding  members  of  the  “  Societa  Italiana  delle  Scienze,  detta  dei  XL.,”  and 
has  also  received  ’heir  first  gold  medal,  instituted  during  the  present  year  by 
the  late  Minister  of  Public  Instruction,  Signor  Matteucci,  to  honour  the  most 
important  discoveries  in  physical  science. 

The  president,  in  his  address,  says: 

“  I  will  not  here  pass  in  review  the  various  memoirs  in  physics  which  you 
have  published  in  the  ‘  Philosophical  Transactions,’ since  all  carry  the  impres¬ 
sion  of  the  inventive  genius  which  ever  distinguishes  all  that  you  have  done. 
I  cannot,  however,  refrain  from  calling  to  mind  that  to  you  we  owe  the  dis¬ 
covery  of  the  method,  as  ingenious  as  it  is  original,  for  measuring  the  velocity 
of  electric  currents  and  the  duration  of  the  spark. 


IVHEA  TSTONE  E  TEL E GRAPHS. 


427 


“The  applications  of  the  principle  of  the  rotating  mirror  are  so  important 
and  so  various  that  this  discovery  must  be  considered  as  one  of  those  which 
have  most  contributed  in  these  latter  times  to  the  progress  of  experimental 
physics. 

“  Not  less  ingenious  was  the  invention  of  the  stereoscope  and  of  the  modes 
by  which  binocular  vision  is  effected,  which  enable  us  to  obtain  the  percep¬ 
tion  of  relief  from  the  simultaneous  observation  of  two  plane  images. 

“  Also  the  memoir  on  the  measure  of  electric  currents,  and  on  all  the  ques¬ 
tions  which  relate  thereto  and  to  the  laws  of  Ohm,  has  powerfully  contributed 
to  spread  among  physicists  the  knowledge  of  those  facts  and  the  mode  of 
measuring  them  with  an  accuracy  and  simplicity  which  before  we  did  not 
possess. 

“All  physicists  know  how  many  researches  have  since  been  undertaken 
with  your  rheostat  (see  p.  333)  and  with  the  so-called  Wheatstone’s  bridge, 
and  how  usefully  these  instruments  have  been  applied  to  the  measure  of  elec¬ 
tric  currents,  of  the  resistance  of  circuits,  and  of  electro  motive  forces. 

“  And  here  it  would  be  impossible  to  leave  out  of  view  that  to  you  we  prin¬ 
cipally  owe  the  practical  invention  and  the  true  realization  of  the  electric 
telegraph. 

“  Finally,  I  would  call  to  mind  your  recent  researches  on  the  augmentation 
of  the  force  of  a  magnet  by  the  reaction  which  its  own  induced  currents 

exert  upon  it. 

“All  these  great  acquisitions,  procured  by  you,  to  physical  science  render 
you  well  worthy  of  this  distinction  from  the  Italian  Society  of  Sciences. 

“  Preserve  yourself  in  health  and  activity,  and  your  country  and  all  your 
admirers  and  friends  are  certain  to  find,  in  the  discoveries  still  to  be  added 
while  you  continue  to  work,  some  compensation  for  that  immense  and  irrepa¬ 
rable  loss  which  natural  philosophy  has  received  by  the  death  of  Faraday.” 

In  addition  to  the  memoirs  by  Sir  Charles  Wheatstone,  alluded  to  by  Signor 
Matteucci,  the  following  may  be  specially  noticed: 

“On  the  Acoustic  Figures  of  Vibrating  Surfaces,”  published  in  the  “  Philo¬ 
sophical  Transactions”  for  1832.  In  this  memoir,  which  gained  for  Sir  Charles 
his  admission  into  the  Royal  Society,  the  author  gave  for  the  first  time  the 
laws  of  formation  of  the  varied  and  beautiful  figures  discovered  by  Chladni. 
Attention  has  recently  been  revived  to  this  subject  by  Konig  and  others  on 
the  Continent. 

“On  the  Transmission  of  Sound  through  Solid  Conductors ”  (  ‘Journal  of 
the  Royal  Institution,”  1828).  This  memoir  describe^  1  lie  means  discovered 
by  the  author  of  transmitting  musical  performances  to  distant  places. 

“On  the  Prismatic  Analysis  of  Electric  Light”  (British  Association,  1832). 
By  these  experiments  Sir  Charles  proved  for  the  first  time  ihat  l he  spectrum 
of  the  electric  spark  from  different  metals  presented  each  a  definite  series  of 
lines  differing  in  colour  and  position  from  each  other,  and  that  these  appear¬ 
ances  afforded  the  means  of  distinguishing  the  smallest  fragment  of  one  metal 
from  that  of  another.  This  investigation  was  one  of  the  earliest  starting- 
points  of  an  entire  new  branch  of  physical  science,  in  which  there  are  now 
many  distinguished  workers. 

“On  the  Polar  Clock”  (British  Association,  1849).  This  is  an  optical 
instrument  which  indicates  the  time  by  means  of  the  changes  in  the  plane  of 
polarization  of  the  blue  light  of  the  sky  in  the  direction  of  the  pole.  It  is 
founded  on  the  discoveries  of  Arago  and  Quetelet;  and  Arago  states  that 


MAGNETISM. 


42  S 


“  l’honneur  dc  la  construction  de  l’horloge  polaire,  je  la  reconnais  avec  em- 
pressement  et  sans  reserve,  revient  exclusivement  a  M.  Wheatstone.” 

It  would  carry  us  beyond  our  limits  to  enumerate  the  various  inventions 
relating  to  the  electric  telegraph  and  other  applications  of  electricity  which 
have  emanated  from  Sir  Charles.  We  will  mention  two  only. 

We  owe  to  him,  in  addition  to  his  former  inventions  relating  to  the  electric 
telegraph,  the  alphabetical-dial  telegraph,  working  without  any  clockwork 
power,  and  in  which  a  magneto-electric  machine  supplies  the  place  of  a  voltaic 
battery.  These  instruments  were  first  introduced  on  the  Paris  and  Versailles 
Railway  in  1846,  and,  with  the  improvements  which  the  inventor  has  since 
made,  have  been  employed  to  a  great  extent  throughout  the  kingdom  by  the 
Universal  Private  Telegraph  Company  in  furnishing  telegraphic  communica¬ 
tion  between  public  offices  and  private  establishments,  to  which  purposes, 
from  their  facility  of  manipulation  and  constancy  of  action,  they  are  admir- 
*  ably  adapted. 

A  more  recent  invention  is  his  fast-speed  telegraph,  in  which  the  messages, 
previously  prepared  on  strips  of  paper  by  manipulations  as  easy  as  those  for 
sending  an  ordinary  message,  aie,  by  passing  through  a  very  small  machine 
constructed  on  somewhat  the  principle  of  a  Jacquard  loom,  made  to  print  the 
messages  at  the  remote  station  in  the  ordinary  telegraphic  characters,  with  a 
rapidity  and  distinctness  unattainable  by  the  hand  of  an  operator.  The  inven¬ 
tion  of  these  instruments  dates  from  1858;  but  they  have  only,  with  recent 
improvements,  been  practically  introduced,  by  the  Electric  Telegraph  Com¬ 
pany,  during  the  last  year.  Since  June  last  these  instruments  have  been  in 
constant  action  for  the  ordinary  business  of  the  establishment  between  London 
and  Newcastle,  printing  from  sixty  to  a  hundred  and  ten  words  per  minute. 
The  result  has  been  so  successful  that  the  company  have  just  resolved  to  adopt 
them  on  other  leading  lines  of  communication. 

In  the  report  of  the  Paris  Exhibition  of  1855,  honourable  mention  was 
awarded  to  Sir  Charles,  he  being  hors  de  concours ,  for  having  been  the  first  to 
conceive  the  idea,  and  for  having  proposed,  in  1840,  a  means  of  resolving  the 
question,  of  a  submarine  telegraph  between  Dover  and  Calais. 

It  may  be  mentioned  in  reference  to  an  eminent  philosopher,  Sir  David 
Brewster  (whose  loss  we  have  had  to  deplore),  that  one  of  the  last  acts  of  his 
life  was  to  nominate  Wheatstone  for  election  as  an  honorary  member  of  the 
Royal  Society  of  Edinburgh,  thus  falsifying  the  couplet  of  Dryden,  who  says, 

“Forgiveness  to  the  injured  does  belong: 

But  they  ne’er  pardon  who  have  done  the  wrong.” 

In  1868  Wheatstone  received  the  honour  of  knighthood  at  the  hands  of 
his  gracious  sovereign,  and  this  same  year  of  grace  the  Royal  Society  have 
awarded  to  him  their  highest  distinction,  viz.,  the  Copley  medal. 

“This  is  the  state  of  man:  to-day  he  puts  forth 
The  tender  leaves  of  hope ;  to-morrow,  blossoms 
And  bears  his  blushing  honours  thick  upon  him.” 

In  concluding  this  brief  notice  of  the  laborious  and  useful  life  of  Wheat¬ 
stone,  we  may,  in  common  with  all  his  friends  and  admirers,  be  permitted  to 
hope  that  he  may  pass  the  evening  of  his  days  in  peace  and  in  the  enjoyment 
of  health,  and  that  he  will  give  to  the  world,  in  the  calmness  of  matured  age,  a 
monograph  of  the  l'  Labours  of  his  Life.” 

In  every  book  devoted  to  the  consideration  of  electric  telegraph  instruments 


WHEATSTONE'S  TELEGRAPHS. 


429 


we  find  illustrations  and  descriptions  of  Cooke  and  Wheatstone’s  earlier  inven¬ 
tions  of  the  single  and  double  needle  telegraph.  We  will,  therefore,  commence 
at  the  year  1840,  when  he  constructed  the  alphabet-dial  telegraph,  which  the 
writer  has  always  found  to  be  one  of  the  best  forms  for  teaching  and  demon¬ 
strating  the  broad  principles  upon  which  motion  is  developed  by  a  current 
thrown  alternately  from  one  electro-magnet  to  another.  Such  is  the  con¬ 
struction  of  the  telegraph,  the  dial  of  which  is  shown  at  Fig.  375. 


Fig.  375. —  Wheatstone’s  first  Alphabet- 
Dial  Telegraph  (1840). 


Fig.  376.—  Wheatstone’s 
Communicator  ( 1 840). 


It  consists  of  a  circular  dial,  on  which  the  letters  of  the  alphabet  are  painted 
in  black  letters  on  a  white  ground.  The  mechanism  is  very  simple.  Two  electro¬ 
magnets,  with  feeders  and  long  arms,  strike  alternately  the  pallets ;  these  take 
up  at  each  blow  one  tooth  of  a  wheel  or  escapement,  and  every  time  a  tooth 
is  taken  up  the  hand  on  the  dial  moves  forward  one  letter.  To  make  the  letters 
on  the  dial  coincide  with  the  letters  of  the  sender  of  the  message,  another 
instrument  is  required,  called  the  “communicator.”  (Fig.  376.) 

This  consists  of  a  wheel,  upon  the  circumference  of  which  are  thirty  alter¬ 
nations  of  brass  and  ivory  corresponding  to  the  letters  of  the  alphabet,  &c., 
with  which  also  this  instrument  is  provided.  There  are  two  springs,  one  on 
each  side,  which  communicate  alternately  with  the  communicator  and  through 
that  to  the  battery  and  wires  of  the  dial  telegraph.  When  the  communicator 
is  turned  round  one  letter,  the  hand  or  the  dial  moves  one  letter;  and,  if  the 
instruments  are  very  carefully  made,  they  answer  remarkably  well. 

Wheatstone,  however,  found  that  they  sometimes  missed  a  tooth  in  the 
escapement,  and,  of  course,  one  letter  being  gone,  the  message  afterwards 
might  be  very  chaotic,  particularly  when  a  number  of  words  in  rapid  succes¬ 
sion  had  to  be  forwarded.  This  system  was,  however,  at  the  time  adopted  on 
some  of  the  continental  lines. 

Passing  by  the  type-printing  telegraph  of  1841  we  now  come  to  the  new 
magnetic  alphabetic-dial  telegraph  of  1858  and  i860. 

The  reader  will  be  able  to  understand  the  construction  better  by  reading 
and  examining  the  annexed  description  and  diagrams  than  if  a  minute  descrip¬ 
tion  of  the  above  instrument  (Fig.  377)  were  given  at  once.  It  is.  perhaps, 
unnecessary  to  remark  that  these  instruments  are  in  daily  use  by  the  Universal 
Private  Telegraph  Company. 

Instructions  for  connecting-up  the  Instruments. — The  instruments  (commu¬ 
nicator,  indicator,  and  alarum)  at  each  station  should  first  be  placed  in  short 
circuit  in  the  following  manner  (Fig.  378): 

Place  short  wires  upon  the  two  upper  terminals,  a  b ,  at  the  back  of  the  indi- 


430 


MAGNETISM. 


F IG.  377.  —  Wheatstone's  new  Magnetic  Alphabetic-Dial  Telegraph. 

cator,  and  connect  them  with  c  and  d  respectively,  the  switch,  x,  being  turned 
to  point  to  the  letter  T — Telegraph.  The  handle,  z,  of  the  communicator  is 
then  to  be  turned  steadily  at  a  rate  of  about  a  hundred  and  twenty  revolu¬ 
tions  per  minute,  and  the  index  or  pointer  passed  from  -f  to  -T  on  the  dial  by 


Indicator. 


Fig.  378. 


WHEATSTONE'S  TELEGRAPHS. 


43i 


depressing  the  finger-key  opposite  the  full  stop  (.)  and  the  key  opposite  the 
+  immediately  afterwards.  If  the  index  of  both  communicator  and  indicator 
correspond,  the  connections  will  be  right ;  but  should  the  hand  of  the  indi¬ 
cator  be  either  in  advance  or  behind  the  +  one  space,  the  connecting  wires 
must  be  reversed. 


now  be  connected  to  the  instruments  by  removing  one  of  the  short  wires  at 
each  station,  and  substituting  the  line  wire  and  earth  wire,  as  shown  at  a  b 
and  c  d.  The  same  signal  of  passing  the  pointer  from  -|-  to  is  now  to  be 
sent  from  station  to  station,  and  if  the  index  at  the  other  station  falls  either 
one  in  advance  or  behind,  the  position  of  the  line  and  earth  wires  at  one  sta¬ 
tion  only  must  be  reversed. 

The  hand  of  the  indicator  may  be  reset  by  gently  moving  the  small  button 
under  the  face  backward  and  forward  between  the  thumb  and  finger. 

When  more  than  two  stations  require  to  be  connected  up  in  the  same  circuit, 
the  above  rules  are  to  be  observed  with  reference  to  the  signals  from  +  to  + 
at  each  successive  station,  the  connections  appearing  thus  (Fig.  380) — 


LINtl  WIRE. 


432 


MAGNETISM. 


When  several  stations  are  in  the  same  circuit,  it  will  often  be  found  conve¬ 
nient  to  introduce  the  switch,  enabling  the  operator  to  send  up  and  down  the 
line  in  either  direction,  without  interrupting  the  communication  of  those  sta¬ 
tions  situated  in  an  opposite  direction  to  that  in  which  he  is  speaking.  The 


DOWN  LINE.  UP  LINE 


manner  of  connection  will  be  seen  by  reference  to  the  drawing.  This  arrange¬ 
ment  will  enable  several  stations  to  communicate  with  each  other  at  the  same 
time. 

a - b - c - d - e - f - g - h 

For  instance,  while  a  is  speaking  to  b,  c  can  talk  to  d,  e  with  _/",  and  so  on. 
This  system  requires  that  each  station  has  its  own  signal  or  preface  for  calling 
attention,  and  that  when  no  station  is  called  either  up  or  down  the  line,  the 
handle  of  the  switch  remains  on  the  through  circuit ,  as  shown  in  the  diagram. 
The  switch  is  generally  adapted  to  the  peculiar  requirements  of  the  line. 

When  alarums  or  bells  are  used  to  call  attention,  they  must  be  placed  in 
circuit  by  connecting  their  binding-screws  to  the  two  lower  binding-screws  at 
the  back  of  the  indicator.  The  alarum  may  be  placed  at  any  distance  from 
the  instrument,  in  the  most  convenient  position  for  calling  attention.  The 
switch,  x,  of  the  indicator  should  point  to  A,  alarum,  when  no  messages  are 
being  sent,  but  be  turned  to  T  when  operations  begin. 

Instructions  for  working  the  Telegraphs. — The  following  summary  of  rules 
for  working  the  telegraph  may  be  advantageously  introduced  here : 

1.  The  handle  in  front  of  the  instrument  (Fig.  377),  which  causes  the  arma¬ 
ture  of  the  magnet  to  rotate,  must  be  kept  in  continuous  motion  by  one  hand, 
while  the  fingers  of  the  other  are  employed  to  manipulate  the  stops  or  keys. 
Care  must  be  taken  not  to  intermit  the  motion  until  the  end  of  the  message. 

2.  A  key  need  not  be  continuously  pressed  down;  it  will  suffice  merely  to 
touch  it;  but  another  key  must  not  be  pressed  down  until  the  index  or  pointer 
has  arrived  at  the  letter  previously  indicated. 

3.  The  same  key  cannot  be  pressed  twice  down  in  succession ;  to  repeat  a 
letter  it  is  necessary  to  touch  the  preceding  key,  and,  without  waiting  for  the 
arrival  of  the  index,  to  touch  again  the  proper  key. 

4.  Before  commencing  to  send  a  message,  the  index  of  all  the  instruments 
must  point  to  -f-.  To  bring  the  telegraph  to  this  position  when  out,  the  small 


WHEATSTONE'S  TELEGRAPHS. 


433 


pin  or  button  on  the  face  of  the  telegraph  must  be  meved  alternately  back¬ 
wards  and  forwards  between  the  finger  and  thumb  until  the  index  stands  at  +. 

5.  If  by  inadvertence  the  index  of  the  communicator  has  been  left  at  a 
letter,  it  must  be  brought  to  the  cross  before  the  telegraph  is  adjusted. 

6.  The  pointer  of  the  alarum  must  invariably,  when  the  instrument  is  not 
in  use,  be  turned  to  the  letter  A. 

7.  To  call  attention  for  the  purpose  of  sending  a  message,  first  turn  your 
own  alarum  off,  then  rotate  the  handle  of  the  communicator  and  let  the 
needle  pass  from  to  -f-.  This  will  ring  the  bell  at  the  other  end.  Wait 
an  interval  of  time  sufficient  to  allow  of  reply.  If  no  reply,  continue  to  call 
in  the  same  manner. 

8.  Receiver  will  notify  his’  attention  by  repeating  the  signal. 

9.  The  receiver  will  then  turn  off  his  alarum,  by  passing  the  pointer  from 
letter  a  to  T. 

10.  A  short  time  must  be  allowed  the  receiver  before  sending,  to  enable 
him  to  put  his  indicator  in  accord  with  his  transmitter,  if  it  be  wrong. 

11.  At  the  end  of  each  word  the  needle  to  be  brought  to  the  +. 

12.  Should  the  receiver  not  understand,  he  will  send  the  letter  R  for  repeat, 
prior  to  giving  -f .  The  sender  will  then  repeat  the  last  word. 

13.  Every  initial  letter  or  pait  of  a  word  used  for  abbreviation  must  be 
followed  by  the  full  stop,  and  the  full  stop  must  be  given  at  the  end  of  each 
sentence. 

14.  At  the  end  of  message,  needle  to  be  turned  from  -f  to  -T  twice. 

15.  Receiver  to  repeat  this  double  revolution. 

16.  If  by  accident  the  needle  of  the  indicator  becomes  misplaced,  so  as  to 
render  a  message  unintelligible,  the  receiver  must  break  in  by  pressing  down 
several  keys  in  succession.  The  sender  will  immediately  stay  sending.  Both 
receiver  and  sender  will  then  set  needles  at  +  ,and  receiver  will  give  repeat,  R. 

17.  To  signify  figures,  use  the  semicolon,  and  then  the  +,  before  and  aftet 
them. 

Instructions  for  keeping  the  Instruments  in  order. — When  the  telegraph  is 
in  operation,  the  handle  of  the  communicator  should  be  turned  at  a  uniform 
rate  of  1 20  revolutions  per  minute,  and  the  finger-keys  should  not  be  depressed 
when  the  handle  is  at  rest. 

The  working  parts  and  bearings  of  the  communicator  will  require  occasion¬ 
ally  to  be  oiled  with  good  watch-oil,  procured  from  any  respectable  watch¬ 
maker.  If  the  oil  is  good,  and  the  telegraoh  moderately  used,  the  instrument 
will  work  eight  or  ten  months  without  touching;  but,  when  in  constant  use,  it 
is  desirable  to  apply  a  little  oil  regularly  every  two  months.  Access  for  this 
purpose  may  be  obtained  to  the  interior  of  the  communicator  by  unscrewing 
the  bottom  of  the  communicator.  The  various  parts  to  be  oiled  are  shown  in 
the  annexed  diagram  at  a ,  b,  c ,  d;  and  by  dipping  the  point  of  a  penknife 
into  the  oil,  it  may  be  neatly  applied  in  small  quantities  where  desired. 

If  the  centre,  b ,  has  become  worn  by  constant  revolution,  and  causing  the 
armature,  e,  to  touch  the  iron  prolongations  of  the  magnet,  the  handle  will 
work  stiffly  or  stop  altogether.  This  may  be  remedied  by  tightening  slightly 
the  screw,  g  (Fig.  382),  with  a  pair  of  small  pliers,  or  other  means  sufficient 
to  free  the  armature  from  contact  with  the  poles  of  the  magnet. 

After  long  use,  the  watch-chain,  which  runs  round  the  rollers  on  the  lower 
plate,  for  the  purpose  of  mechanically  raising  .each  key,  after  it  has  been 
depressed  by  the  hand,  may  become  too  slack ;  this  is  remedied  by  slightly 

28 


434 


MAGNETISM. 


J, 


tightening  the  screw,  a.  attached  to  a  lever  carrying  an  extra  roller,  care 
being  taken  to  leave  sufficient  slack  in  the  chain  to  allow  of  one  key  always 
remaining  depressed,  as  shown  at  B  (Fig.  383). 


If  it  becomes  necessary  to  take  the  communicator  to  pieces  (this  operation 
had  always  better  be  performed  by  a  clock  or  watch  maker,  or  ot 1  ;r  experi¬ 
enced  person),  the  bottom  of  the  case  must  be  taken  off  first,  ana  the  little 
ivory  number-plate  in  front  of  the  instrument 
pushed  out  from  the  inside.  This  will  enable  the 
position  of  the  wheel  and  pinion  to  be  marked 
through  the  hole  of  the  number-plate,  by  making 
a  scratch  (Fig.  384),  as  at  x,  across  both,  care  being 
taken  in  putting  together  that  the  marked  parts 
of  the  wheels  are  placed  as  before.  The  magnet 
may  then  be  taken  out,  having  previously  un¬ 
screwed  the  wires  leading  from  the  coils.  The 
brass  casing  which  covers  the  upper  portion  of 
the  mechanism  is  now  to  be  unscrewed,  and  the 
ring  with  the  glass,  which  is  only  sprung  on,  re¬ 
moved ;  then  the  dial  card  and  plate.  Unscrew 
the  four  pillars  below,  and,  after  the  whole  frame  has  been  taken  off  the 
wooden  case,  all  may  be  taken  to  pieces.  It  will  be  necessary  to  mark  the 


WHEA  TSTONE  'S  TELE  GRAPHS. 


435 


position  of  the  two  wheels,  h  and  i,  by  a  scratch  across  both,  before  taking 
that  portion  asunder.  Oil  must  be  put  to  the  teeth  of  the  wheel  k,  and  also 
to  n,  in ,  o ,  and  p  (Fig.  385.) 


The  operation  of  putting  together  is  as  follows: — First  put  the  centre  arbor 
and  all  upon  it  in  the  frame,  and  secure  the  same  by  the  four  pillar  screws. 
Then  place  the  finger-keys,  the  dial-plate,  the  springs  for  the  keys,  the  dial, 
the  index,  and  the  glass  together,  and  fix  the  whole  on  the  wooden  case. 
Lastly,  place  the  magnet  in  its  proper  position,  and,  when  all  is  ascertained 
to  be  correct,  screw  on  the  brass  casing  and  the  wooden  bottom  of  the  in¬ 
strument. 

The  indicator  and  alarum  may  be  taken  to  pieces,  when  necessary,  and  put 
together  again,  by  marking  the  proper  position  of  the  several  parts.  In  the 
indicator,  pivots  only  require  to  be  oiled,  and  that  in  very  small  quantities. 
The  indicator,  when  good  oil  has  been  used,  will  work  without  attention  for 
two  or  three  years. 


Fig.  3S6. —  Wheatstone's  Bell  in  box ,  and  ready  for  Military  or  other 

Service. 

Professor  Wheatstone’s  instruments  have  been  adopted  by  the  army  authori¬ 
ties,  and  are  made,  as  in  Fig.  377,  p.  397,  very  portable  and  wholly  independent 

28 — 2 


43<> 


MAGNETISM. 


of  all  battery  power,  the  trouble  of  putting  batteries  together,  the  supply  of 
acids,  breakage,  and  all  the  trouble  that  would  be  multiplied  tenfold  in  the 
hurry  of  the  battle-field.  These  instruments,  as  already  described,  work  by  3 
current  developed  by  magnetism  and  by  the  use  of  steel  magnets  ;  they  are 
made  very  strong  and  substantial,  and  are  well  calculated  to  bear  the  wear 
and  tear  of  military  operations  conducted  in  the  field. 

The  bell  is  rung,  as  nearly  all  other  electric  bells  are  rung,  by  clockwork 
wound  up,  but  stopped  by  a  “  detainer.”  Directly  the  detent  is  removed  by 
the  current,  the  bell  rings. 

The  same  instruments,  connected  with  enlarged  dials,  are  used  on  board 
the  iromclads.  We  show  an  enlarged  dial,  and  can  easily  understand  how 
quickly  the  commander’s  orders  could  be  conveyed  to  the  engine-room. 


Fig.  387. —  Wheatstone’s  enlarged  Dials ,  such  as  are  used  in  the  Engine- 

rooms  of  Ships  of  War. 


The  dials,  of  course,  would  have  special  orders  printed  on  them,  being  those 
given  constantly  in  the  navigation  of  these  immense  vessels. 

In  a  very  short  time,  similar  dials  will  be  placed  in  the  various  rooms  occu¬ 
pied  by  members  in  the  House  of  Commons,  and  the  dials  will  show  what 
business  is  in  progress  and  what  has  been  done.  The  business  to  be  trans¬ 
acted,  being  printed  in  a  circular  form,  is  laid  upon  the  dial,  and  the  hand 
points  to  that  in  progress,  whilst  all  behind  it  is  over. 

The  steering  of  the  iron-clads  is  also  to  be  conducted  with  the  assistance  of 
similar  dials. 

One  of  the  most  useful  of  Sir  Charles  Wheatstone’s  elegant  and  beautiful 
inventions  is  the  instrument  he  has  supplied  to  the  editor  of  “The  Times’ 
newspaper  to  record  the  number  of  copies  printed  and  printing.  The  editor 


IVHEA  TSTONE  'S  TELE  GRAPHS. 


437 


reads  in  his  own  room  the  progress  of  that  great  undertaking,  the  daily  print¬ 
ing  of  “  The  Times.’' 


tlG.  388. —  Wheatstone1  s  Recording  Instrument  for  Newspaper  Offices  or 

Public  Buildings. 

This  instrument  will  record  from  ten  thousand  to  one  million  copies.  The 
same  contrivance  the  writer  hopes  to  be  able  to  adopt  at  the  Polytechnic,  so 
that,  without  moving  from  his  office,  he  will  be  able  to  know  the  number  of 
persons  in  the  building. 

These  instruments  culminate  to  their  highest  degree  of  perfection  in  the 
inventions  of  1858  and  1867,  viz.,  Wheatstone’s  Fast-speed  Automatic  Tele¬ 
graph,  of  which  the  inventor  gives  the  following  particulars: 

“  My  invention  consists  of  a  new  combination  of  mechanism  for  the  purpose 
of  transmitting  through  a  telegraphic  circuit  messages  previously  prepared, 
and  causing  them  to  be  recorded  or  printed  at  a  distant  station.  Long  strips 
or  ribbons  of  paper  are  perforated,  by  a  machine  constructed  for  the  purpose, 
with  apertures  grouped  to  represent  the  letters  of  the  alphabet  and  other  signs. 
A  strip  thus  prepared  is  placed  in  an  instrument,  associated  with  a  rheomotor 
(or  source  of  electric  power),  which  on  being  set  in  motion  moves  it  along, 
and  causes  it  to  act  on  two  pins  in  such  manner  that,  when  one  of  them  is 
elevated,  the  current  is  transmitted  to  the  telegraphic  circuit  in  one  direction, 
and  when  the  other  is  elevated,  it  is  transmitted  in  the  opposite  direction  ;  the 
elevations  and  depressions  of  the  pins  are  governed  by  the  apertures  and 
intervening  intervals.  These  currents,  following  each  other  indifferently  in  the 
two  opposite  directions,  act  upon  a  printing  or  writing  instrument  at  a  distant 
station,  in  such  manner  as  to  produce  corresponding  marks  on  a  ribbon  of 
paper  moved  by  appropriate  mechanism. 

“  1  will  proceed  to  describe  more  particularly  the  several  parts  of  this  tele¬ 
graphic  system,  observing,  however,  that  each  part  has  its  independent  origi¬ 
nality,  and  may  be  associated  with  other  apparatus  already  known. 

“The  first  improvement  consists  of  an  instrument  for  perforating  the  slips 


43§ 


MAGNETISM. 


of  paper  with  the  apertures  in  the  order  required  to  form  the  message.  The 
slip  of  paper  passes  through  a  guiding  groove,  at  the  bottom  of  which  an 
opening  is  made  sufficiently  large  to  admit  of  the  to-and-fro  motion  of  the 
upper  end  of  a  frame  containing  three  punches,  the  extremities  of  which  are 
in  the  same  transverse  line.  Each  of  these  punches  is  capable  of  being  sepa¬ 
rately  elevated  by  an  appropriate  finger-key.  By  the  pressure  of  either  finger- 
key,  besides  the  elevation  of  its  corresponding  punch  in  order  to  perforate  the 
paper,  two  different  movements  are  successively  effected — first,  the  raising  of 
a  clip,  which  holds  the  paper  firmly  in  its  place,  and,  secondly,  the  advancing 
motion  of  the  frame  containing  the  three  punches,  by  which  the  punch  which 
is  raised  carries  the  ribbon  of  paper  forward  the  proper  distance  during  the 
reaction  of  the  key  consequent  on  the  removal  of  the  pressure  ;  the  clip  first 
fastens  the  paper,  and  then  the  frame  falls  back  to  its  normal  position.  The 
two  external  keys  and  punches  are  employed  to  make  the  holes  which,  grouped 
together,  represent  letters  and  other  characters,  and  the  middle  punch  to  make 
holes  which  mark  the  intervals  between  the  letters.  The  perforations  in  the 
slip  of  paper  appear  thus : 


Fig.  389. 


“  The  second  improvement  consists  of  an  apparatus  which  may  be  called 
the  transmitter,  the  object  of  which  is  to  receive  the  slips  of  paper  prepared 
by  the  previously  described  instrument  or  perforator,  and  to  transmit  the  cur¬ 
rents  produced  by  a  voltaic  battery  or  othei  rheomotor  in  the  order  and  direc¬ 
tion  corresponding  to  holes  perforated  in  the  slip  ;  this  it  effects  by  mechanism 
somewhat  similar  to  that  by  which  the  perforator  performs  its  functions.  An 
eccentric  produces  and  regulates  the  occurrence  of  three  distinct  movements; 
1st,  the  to-and-fro  motion  of  a  small  frame,  which  contains  a  groove  fitted  to 
receive  a  slip  of  paper,  and  to  carry  it  forward  by  its  advancing  motion  ;  2nd, 
the  elevation  and  depression  of  a  spring  clip,  which  holds  the  slip  of  paper 
firmly  during  the  receding  motion,  but  allows  it  to  move  freely  during  the 
advancing  motion  ;  3rd,  the  simultaneous  elevation  of  three  wires  placed 
parallel  to  each  other,  resting  at  one  of  their  ends  on  the  axis  of  the  excentric, 
and  their  free  ends  entering  corresponding  holes  in  the  grooved  frame;  these 
three  wires  are  not  fixed  to  the  axis  of  the  excentric,  but  each  of  them  rests 
against  it  by  the  upward  action  of  a  spring,  so  that  when  a  light  pressure  is 
exerted  on  the  free  ends  of  either  of  them,  it  is  capable  of  being  separately 
depressed.  When  the  slip  of  paper  is  not  inserted,  and  the  excentric  is  in 
action,  a  pin  attached  to  each  of  the  external  wires  passes,  during  each  ad¬ 
vancing  and  receding  motion  of  the  frame,  from  contact  with  one  spring  into 
contact  with  another  spring,  and  an  arrangement  is  adopted,  by  means  of 
insulations  and  contacts  properly  applied,  by  which,  while  one  of  the  wires  is 
depressed  and  the  other  remains  elevated,  the  current  passes  from  the  voltaic 
battery  to  the  telegraphic  circuit  in  one  direction,  and  passes  in  the  other 
direction  when  the  wire  before  elevated  is  depressed,  and  vice  versdj  but  while 
both  wires  are  simultaneously  elevated  or  depressed,  the  passage  of  the  cur¬ 
rent  is  interrupted.  When  the  prepared  slip  of  paper  is  inserted  in  the  groove, 
and  moved  onwards,  whenever  the  end  of  one  of  the  wires  enters  an  aperture 


IV HE  A  TSTONE  'S  TELEGRAPHS. 


439 


in  its  corresponding  row,  the  current  passes  in  one  direction,  and  when  the 
end  of  the  other  wire  enters  an  aperture  of  the  other  row,  it  passes  in  the 
other  direction  ;  by  this  means  the  currents  are  made  to  succeed  each  other 
automatically  in  the  proper  order  and  direction  to  give  the  requisite  variety  of 
signals.  The  middle  wire  only  acts  as  a  guide  to  the  paper  during  the  cessa¬ 
tion  of  the  currents. 

“The  wheel  which  drives  the  excentric  may  be  turned  by  hand  or  by  the 
application  of  any  motive  power.  Instead  of  a  voltaic  battery,  a  magneto¬ 
electric  or  an  electro-magnetic  machine  may  be  employed  as  the  source  of 
electric  power.  In  this  case  the  transmitter  and  the  magneto-electric  or 
electro-magnetic  machine  form  a  single  apparatus  moved  by  the  same  power, 
and  they  are  so  adapted  to  each  other,  that  the  shocks  or  currents  are  pro¬ 
duced  at  the  moments  the  pins  of  the  transmitter  enter  the  apertures  of  the 
perforate'd  paper. 

“The  transmitters  just  mentioned  require  only  a  single  wire  of  communica¬ 
tion,  and  currents  in  both  directions  are  available  for  printing  the  signals ;  but 
in  some  cases  it  may  be  advantageous  to  employ  two  telegraphic  wires,  and  to 
use  the  inversions  of  current  to  bring  back  the  pens  or  markers  without  the 
aid  of  reacting  springs.  In  this  case  the  only  modification  of  the  apparatus 
required  is  in  the  disposition  of  the  insulations  and  contacts  necessary  to  trans¬ 
mit  in  their  proper  order  the  currents  from  the  rheomotor  into  the  two  wires. 

“The  third  improvement  is  in  the  recording  or  printing  apparatus,  which 
prints  or  impresses  legible  marks  on  a  strip  of  paper,  corresponding  in  their 
arrangement  with  the  apertures  in  the  perforated  paper.  The  pens  or  styles 
are  depressed  and  elevated  by  their  connection  with  the  moving  parts  of  the 
electro-magnets;  they  are  entirely  independent  of  each  other  in  their  action, 
and  arc  so  arranged  that,  when  the  current  passes  through  the  coils  of  the 
electro-magnets  in  one  direction,  one  of  the  pens  is  depressed,  and  when  it 
["asses  in  the  contrary  direction  the  other  pen  is  depressed  ;  when  the  currents 
cease,  light  springs  restore  the  pens  to  their  usual  elevated  positions.  The 
mo  le  of  supplying  the  pens  with  ink  is  as  follows  : — A  reservoir,  about  an 
eighth  of  an  inch  deep,  and  of  any  convenient  length  and  breadth,  is  made  in 
a  piece  of  metal,  the  interior  of  which  may  be  gilt,  in  order  to  avoid  the  corro¬ 
sive  action  of  the  ink  placed  in  it.  At  the  bottom  of  this  reservoir  are  two 
holes,  sufficiently  small  to  prevent  by  capillary  attraction  the  ink  from  flowing 
th  ough  them.  The  ends  of  the  pens  are  placed  immediately  above  these 
small  apertures,  which  they  enter  when  the  electro  magnets  act  upon  them, 
carrying  with  them  a  sufficient  charge  of  ink  to  make  a  legible  mark  on  the 
strip  of  paper  passing  beneath  them.  The  motion  of  the  paper  ribbon  is  pro¬ 
duced  and  regulated  by  apparatus  similar  to  those  employed  in  other  register 
or  printing  telegraphs. 

“Instead  of  reacting  springs  for  restoring  tfie  position  of  the  pens,  the 
attractive  or  repelling  force  of  small  permanent  magnets  may  be  employed. 
All  the  essential  parts  of  my  new  recording  or  printing  telegraph  are  included 
in  the  previously  mentioned  three  improvements.  The  following  improve¬ 
ments  are  either  auxiliary  or  substitutions  for  parts  already  mentioned. 

“  The  fourth  improvement  is  an  instrument  which  I  call  a  translator  ;  its 
object  is  to  translate  the  telegraphic  signs,  consisting  of  successions  of  points 
or  marks,  adopted  in  this  system,  into  the  ordinary  alphabetic  characters.  In 
the  system  I  have  adopted,  limiting  the  number  of  points  in  succession  to  four, 
thirty  distinct  characters  are  represented. 


MAGNETISM. 


^40 


“The  instrument  presents  externally  nine  finger-stops,  eight  of  which  are 
arranged  in  two  parallel  rows,  four  in  each,  and  the  remaining  one  is  placed 
separately. 

“  The  principal  part  of  the  mechanism  within  is  a  wheel,  on  the  circum¬ 
ference  of  which  thirty  types  are  placed  at  equal  distances,  representing  the 
letters  of  the  alphabet  and  other  characters ;  other  mechanism  is  so  disposed 
and  connected  thereto,  that  when  the  keys  of  the  upper  row  are  respectively 
depressed,  the  wheel  is  caused  to  advance  1,  2,  4,  or  8  steps  or  letters,  and 
when  those  of  the  lower  row  are  in  like  manner  depressed,  the  wheel  advances 
respectively  2,  4,  8,  or  16  steps.  By  this  disposition,  when  the  stops  are  touched 
successively  in  the  order  in  which  the  points  are  printed  on  the  paper — touch¬ 
ing  the  first  stop  for  one  point,  the  first  and  second  for  two  points,  &c.,  and 
selecting  the  stops  of  the  upper  or  lower  row,  according  as  the  point  is  in  the 
upper  or  lower  row  of  the  printed  ribbon — the  type  wheel  will  be  crought  into 
the  proper  position  for  placing  the  letter  corresponding  to  the  succession  of 
points  over  a  ribbon  of  paper.  The  ninth  stop,  when  it  is  pressed  down,  acts 
to  impress  the  type  on  the  paper,  to  cause  the  advance  of  the  paper,  in  order 
to  bring  a  fresh  place  beneath  the  type-wheel,  and  subsequently  to  restore 
the  type-wheel  to  its  initial  position. 

“  The  fifth  improvement  is  a  modification  of  the  electro-magnets  of  the 
instrument  of  the  third  improvement,  which  enables  the  pens  to  go  back  to 
their  normal  positions  when  the  currents  in  the  telegraphic  circuit  cease,  with¬ 
out  the  aid  of  reacting  springs  or  permanent  magnets.  An  extra  coil  of  wire 
is  wound  round  each  of  the  electro-magnetic  bars,  which  act  on  one  side  of 
each  of  the  double  magnetic  needles  appropriated  to  me  two  pens.  These 
coils  are  entirely  insulated  from  those  connected  with  the  telegraphic  circuit, 
and  form  together  a  short  local  circuit,  in  which  a  feeble  voltaic  current  con¬ 
tinually  circulates,  in  consequence  of  the  interposition  of  a  small  rheomotor; 
by  this  current  the  needles  are  held,  when  no  current  exists  in  the  telegraphic 
circuit,  constantly  attracted  towards  these  electro-magnets.  When,  however, 
the  current  transmitted  through  the  telegraphic  circuit  acts  on  the  coils,  besides 
its  direct  action  to  cause  the  deflection  of  one  of  the  double  needles  and  the 
detention  of  the  other,  it  neutralizes  the  current  of  the  local  battery  in  that 
electro  magnet  where  its  effect  for  the  time  would  be  disadvantageous. 

“  The  sixth  improvement  consists  in  the  application  of  ribbons  of  paper 
prepared  by  the  perforator,  and  passed  through  the  transmitter  as  heretofore 
described,  to  produce  the  successive  motions  of  a  magnetic  needle  or  needles 
corresponding  to  the  signals  required,  whether  separately  employed  for  this 
purpose  or  in  conjunction  with  the  printing  apparatus  already  mentioned.” 

Even  these  beautiful  instruments  were  not  considered  perfect  by  the  inde¬ 
fatigable  inventor,  and  we  again  find  him,  after  a  most  severe  illness,  recording, 
in  1867,  further  great  improvements  in  the  mechanism  of  all  their  parts. 

Improvements  in  Electric  Telegraphs,  and  in  Apparatus 

CONNECTED  THEREWITH. 

“My  present  invention-(i867)  consists  in  certain  improvements  in  the  various 
instruments  constituting  the  electric  telegraph  system  described  in  the  speci¬ 
fication  of  the  patent  granted  to  me  on  the  second  day  of  June,  A.D.  1858, 
No.  1239. 

“This  system  comprises  three  distinct  apparatuses:  first,  a  perforating 


WHEATSTONE’S  TELEGRAPHS. 


441 


machine  for  preparing  the  messages  to  be  sent  on  the  strips  of  paper  or 
other  suitable  material ; 

“Second,  a  transmitter,  or  apparatus  for  receiving  the  strips  of  paper  so 
prepared,  and  for  transmitting  the  currents  produced  by  a  voltaic  battery, 
magneto-electric  machine,  or  other  rheomotor,  in  the  order  corresponding  to 
the  holes  perforated  in  the  strip,  the  direction  and  sequence  of  these  currents 
being  governed  by  pins,  or  other  suitable  apparatus,  disposed  so  as  to  enter 
the  perforations,  and  operating  in  a  manner  analogous  to  that  in  the  mechanism 
of  a  Jacquard  loom,  and  the  strip  being  advanced  intermittingly  by  the  action 
of  pins  or  other  apparatus  appropriated  for  that  purpose; 

“  And,  third,  of  a  recording  or  printing  apparatus  adapted  to  print  or  impress 
marks  on  a  strip  of  paper,  such  marks  corresponding  in  their  arrangement 
with  the  currents  transmitted  to  the  telegraphic  line  and  with  the  apertures 
in  the  perforated  paper. 

“  Having  separately  described  each  system  of  recording  telegraphs,  with  the 
improvements  which  form  the  objects  of  the  present  specification,  1  proceed 
to  designate  those  points  which  I  specially  claim  as  new. 

“  First,  the  modification  of  the  perforator  for  the  dot-printing  telegraph, 
which  enables  it  to  prepare  the  strips  of  paper  with  an  uninterrupted  series 
of  central  apertures;  this  modification,  described  as  the  first  improvement, 
consists  of  the  mechanism  being  so  arranged  that  when  either  of  the  keys 
corresponding  with  the  outer  apertures  is  depressed,  besides  acting  on  its  own 
punch,  it  carries  with  it  the  punch  which  corresponds  with  the  central  apertures, 
while  the  latter  is  alone  acted  upon  by  means  of  another  key  causing  the  per¬ 
foration  only  of  a  single  aperture  at  a  time. 

“Second,  the  modification  of  the  perforator,  described  as  the  fourth  improve¬ 
ment,  having  five  punches,  and  the  mechanism  so  arranged  that,  when  the  first 
key  is  pressed,  three  of  the  punches  in  the  order  described  are  simultaneously 
acted  upon  ;  when  a  second  key  is  depressed,  four  of  the  punches  are  in  like 
manner  simultaneously  acted  upon ;  and  when  a  third  key  is  depressed,  the 
single  punch  only  of  the  central  line  is  acted  upon.  1  claim  also,  in  connec¬ 
tion  with  this  arrangement,  the  mechanism  by  which  when  either  the  first  or 
third  keys  are  pressed  down  the  paper  advances  only  a  single  space,  and  when 
the  second  key  is  depressed  it  advances  two  spaces;  but  be  it  understood  that 
I  do  not  claim  the  advance  of  the  paper  by  unequal  spaces,  unless  in  connec¬ 
tion  with  the  arrangement  of  the  punches  described. 

“Third,  the  additions  of  extra  keys  to  the  preceding  modification  of  the 
perforator,  with  additional  punches,  described  in  the  fifth  improvement,  which 
arc  so  arranged  that  each  additional  key  when  depressed,  while  it  punches 
simultaneously  all  the  required  apertures,  shail  advance  the  paper  at  once 
three,  four,  or  more  steps,  so  that  all  the  perforations  may  be  simultaneously 
made  which  are  necessary  to  cause  lines  of  the  various  required  lengths  to  be 
marked  or  printed  by  the  receiving  instrument. 

“  Fourth,  the  modification  of  the  transmitter,  described  as  the  second  im¬ 
provement,  whether  actuated  by  a  magneto-electric  machine  or  ny  a  voltaic 
battery,  in  which  the  central  needle  alone  has  a  to-and-fro  motion  for  the 
purpose  of  propelling  forward  the  strip  of  paper  by  means  of  the  central 
apertures  alone,  and  not  also  by  means  of  the  external  apertures  and  outer 
pins,  as  described  in  the  second  improvement  of  the  specification  of  my  patent, 
No.  1239  (a.o.  1S58). 

“  Fifth,  the  modification  of  the  transmitter,  described  as  the  sixth  improve- 


* 


442  MAGNE1ISM. 


ment,  which  is  adapted  to  send  into  the  telegraphic  circuit  short  currents  at 
various  intervals  and  alternately  in  opposite  directions,  so  as  to  determine  the 
occurrence  of  printed  lines  and  intervals  of  various  lengths  in  the  receiving 
instrument :  in  this  modification  one  current-governing  needle  has  a  to-and- 
fro  motion  simultaneously  with  the  central  needle,  while  the  other  has  no  such 
motion,  the  latter  acting  only  while  the  paper  is  at  rest,  and  the  former  while 
it  is  in  motion. 

“  Sixth,  the  modification  of  the  transmitter,  described  as  the  eighth  improve¬ 
ment,  which  is  suited  to  send  into  the  telegraphic  circuit  currents  of  various 
lengths  in  one  direction  only  in  a  different  way  to  that  described  as  the  seventh 
improvement  in  my  patent,  No.  2462  (a.d.  i860).  The  characteristics  of  this 
new  method  are,  first,  that  lines  of  any  lengths  can  be  produced,  instead  of 
lines  of  two  different  lengths  only;  second,  that  the  short  lines  occupy  a 
shorter  space  on  the  paper  than  the  long  lines  do  ;  and,  third,  that  strips  of 
paper  prepared  by  the  perforators  of  the  third  and  fourth  improvements  may 
be  employed  to  regulate  the  motions  of  the  needles  in  order  to  produce  the 
required  effects. 

“  Seventh,  the  modification  of  the  dot-printing  receiving  instrument,  de¬ 
scribed  as  the  third  improvement,  in  which  the  pens  or  markers  are  acted 
upon  by  one  set  of  electro-magnets  and  magnetic  bars,  instead  of  by  two 
sets,  as  described  in  the  specification  of  my  pateni,  No.  1259  (a.D.  1858). 

“  Eighth,  that  modification  of  the  printing  apparatus  of  the  receiving  instru¬ 
ments  of  the  second  and  third  systems  described  as  the  eighth  improvement, 
by  means  of  which  lines  of  various  lengths  are  printed  with  great  rapidity, 
certainty,  and  distinctness.  The  characteristic  distinction  of  this  mode  of 
printing  is,  that  the  inking-disc  and  tracing-disc  are  both  independently  kept 
in  motion  by  the  maintaining  power,  and  are  not  in  actual  contact  with  each 
other,  and  that  the  ink  is  retained  on  the  circumference  of  the  inking-disc  by 
capillary  attraction.” 

We  now  give  the  description  of  the  three  instruments: 

I.  The  perforator. 

II.  The  transmitter. 

III.  The  recorder. 


IV HE  A  TSTONE  'S  TELEGRAPHS. 


443 


placed  transversely  to  the  path  of  the  paper  through  the  machine.  Three  lever 
finger-keys  act  upon  the  punches  in  such  a  manner  that  whenever  either  of  the 
outer  keys  is  depressed,  it  acts  upon  the  punch  which  belongs  to  it,  and  at  the 


same  time  carries  with  it  the  middle  punch  by  means  of  a  collar  which  is  fixed 
thereto,  and  simultaneously  perforates  the  two  apertures ;  but  the  depression 
of  the  middle  key  acts  upon  the  middle  punch  alone,  and  perforates  a  middle 
aperture  only,  which  is  equivalent  to  a  space  in  the  receiving  instrument. 
On  the  removal  of  pressure  from  any  finger-key,  the  corresponding  punch  or 
punches  is  or  are  restored  to  its  or  their  normal  positions  by  means  of  a  re¬ 
acting  spring  or  springs.  A  lever  and  link  arrangement,  moved  by  either  of 
the  three  keys,  draws  back  the  paper-moving  lever  during  the  depression  of  a 
key;  the  release  of  a  key  permits  a  reacting  spring  to  force  the  paper-mov¬ 
ing  lever  forwards  and  to  advance  the  paper  one  step,  the  said  lever  having 
a  rough  end  next  to  the  paper  strip  for  that  purpose:  this  mechanism  propels 
the  paper  quite  independently  of  the  middle  row  of  holes. 

“  Fig.  392  is  a  perspective  view  of  a  transmitter  arranged  to  work  with  two 
line  wires  ;  in  this  instrument,  besides  the  necessary  change  in  the  insulations 
and  contacts,  the  mechanical  arrangements  are  slightly  varied,  the  construc¬ 
tion  shown  being  more  convenient  when  two  line  wires  are  employed  than 
that  first  described,  a  is  a  permanent  magnet,  and  b  is  an  armature  mounted 
on  an  axis  c,  so  as  in  revolving  to  pass  in  front  of  the  poles  of  the  magnet. 
On  the  axis  c  there  is  a  toothed  wheel,  d,  which  drives  the  pinion  e  on  the 
vertical  axis  f  so  that  this  axis  makes  twice  as  many  revolutions  as  the  axis  c ; 
at  the  upper  end  of  the  axis  f  is  a  cam,  g,  arranged  to  act  on  the  pin  h,  which 
is  mounted  on  a  rocking-frame  similar  to  the  rocking-frame  of  the  transmitter 
already  described.  The  pin  h  is  kept  in  contact  with  its  cam  g  by  a  spring  i. 
The  form  of  the  cam  is  such  that  the  forward  motion  of  the  frame  is  gradual, 
but  its  return  motion  takes  place  as  rapidly  as  the  spring  i  will  react,  j  is 
another  cam  on  the  axis  f ;  it  comes  in  contact  with  a  projection  on  the  lever 
k  just  as  the  return  motion  of  the  rocking-frame  is  going  to  take  place,  and 
so  causes  this  lever  to  draw  down  the  three  needles  carried  by  this  frame.  At 
the  same  time  the  tail  of  the  lever  k  presses  on  the  end  of  another  lever  /, 
which  is  fixed  to  the  spring-clip  /«,  and  so  causes  the  clip,  by  turning  slightly 
on  its  axis,  to  nip  the  paper  under  it.  It  will  be  seen  that  the  two  outside  needles 
carried  by  the  rocking-frame  have  projections  from  their  lower  ends,  and  when 
they  are  allowed  to  rise  by  the  perforated  paper,  as  before  explained,  their  ends 
come  in  contact  with  the  springs  n  and  o,  which  are  insulated  from  the  rest  of 
the  instrument,  and  are  in  communication  with  the  two  line  wires.  On  the 


444 


MAGNETISM. 


i 


Fig.  392. —  The  Transmitter  (1858). 


axis  c  a  metal  disc  is  mounted  ;  it  is  made  in  two  parts,  p  and  q,  which  are 
insulated  from  each  other  and  from  the  axis,  r  and  s  are  two  springs,  which 
press  on  the  periphery  of  the  disc  as  it  revolves;  the  spring  r  is  in  metallic 
communication  with  the  working  parts  of  the  instrument,  and  th°  spring  s  is 
insulated  from  these  parts,  but  is  put  into  metallic  connection  with  the  earth. 
When  one  of  the  needles  of  the  rocking-frame  comes  into  contact  with  its 
corresponding  spring,  n  or  o,  it  brings  the  line  wire  in  connection  with  the 
spring  into  metallic  communication  with  the  working  parts  of  the  instrument, 
and  any  currents  or  shocks  transmitted  to  these  flow  into  the  line  wire.  From 
the  construction  of  the  apparatus,  the  contact  between  the  needles  of  the 
rocking-frame  and  their  corresponding  springs  when  established  lasts  during 
half  a  revolution  of  the  axis  c,  and  in  this  period  two  currents  in  opposite 
directions  are  transmitted  into  the  line  wire.  The  first  current  acts  to  bring 
one  of  the  pens  or  markers  of  the  receiving  instrument  into  contact  with  the 
surface  to  be  marked,  and  the  second  current  to  bring  this  pen  or  marker  to 
its  original  position.  It  is  evident  that,  if  necessary,  the  instrument  above 
described  may  be  worked  with  one  line  wire  only,  without  any  change  being 
made  in  the  instrument;  all  that  is  necessary  is  that,  in  perforating  the  strip 


IVHEA  TSTONE  ’S  TELEGRA  PHS. 


445 


for  the  message,  only  one  of  the  outside  finger-keys  of  the  perforator  should 
be  employed  (the  alphabet  or  signs  employed  being  modified  accordingly). 
Or  the  perforating  instrument  and  the  transmitting  instrument  may  both  be 
modified,  if  desired,  so  as  to  be  suitable  only  for  working  with  one  line  wire, 
by  constructing  the  perforator  with  two  in  place  of  three  finger-keys  and 
punches,  and  the  transmitter  with  two  in  place  of  three  needles.” 


Fig.  393. — The  Recording  or  Printing  Instrument  ( 1 85 8). 


Another  improvement  is  in  the  recording  or  printing  apparatus;  but  as 
the  chief  parts  of  this  instrument  have  already  been  described  with  sufficient 
minuteness,  it  is  only  necessary  to  refer  our  readers  to  page  406  for  the  details 
of  the  beautiful  mechanism  which  regulates  the  marking  of  the  slips  of  paper 
and  the  supply  of  ink  to  the  dotting  apparatus. 

The  improved  instruments  are  now  working  between  London  and  New¬ 
castle,  Edinburgh,  Manchester,  and  Glasgow;  and  they  can  send  and  print 
messages  from  seventy  to  one  hundred  and  twenty  words  per  minute ,  accord¬ 
ing  to  their  exigences.  They  are  also  used  in  connection  with  the  submarine 
cable  extending  from  Newcastle  to  Denmark. 


446 


MAGNETISM. 


SIR  CHARLES  WHEATSTONE’S  LAST  AND  MOST  COMPLETE 
TELEGRAPHIC  APPARATUS, 

And  other  beautiful  Applications  of  Electricity — The  Chrono- 
scope  and  Telegraph  Thermometer  for  Great  Altitudes. 


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WHEA  TSTONE  ’S  TELEGRAPHS. 


447 


When  Sir  Charles  Wheatstone  turned  his  attention  to  fast-speed  telegraphs, 
the  result  was  the  dot  printing.  He  attained  700  letters  per  minute;  but  the 
telegraph  companies  objected  to  it,  because  it  necessitated  the  clerks  learning 
the  new  alphabet,  the  dots  being  in  two  lines  (No.  1,  Fig.  A),  the  lower  dot 
taking  the  place  of  the  dash  in  the  line  or  Morse  alphabet.  In  addition  to  the 
above  objections,  it  is  not  suited  for  submarine  cables  requiring  reversals  for 
rapid  working ;  therefore,  Sir  Charles  brought  out  a  transmitter  to  work  the 
inking  Morse.  But  words  could  be  transmitted  quicker  than  the  instrument 
would  print ;  therefore,  it  remained  for  Sir  Charles  to  bring  out  a  rapid  printer, 


Fig.  B. —  The  Line-printing  Transmitter. 


which  he  accomplished,  and  it  is  now  known  by  the  name  of  the  “line-printer,” 
printing  the  dot  and  dash  alphabet  (No.  3,  Fig.  A),  such  as  is  used  by  all  tele¬ 
graph  companies,  printing  600  letters  per  minute;  the  dot  and  line  printing 
differing  especially  in  this  respect — the  line  currents  always  being  inverted 
alternately;  in  the  dot,  three  or  four  currents  in  the  same  direction  sometimes 
follow  each  other. 

The  Line  Transmitter  with  Maintaining  Power  (Fig.  b),  is  a  modi¬ 
fication  of  the  transmitter  described  as  the  sixth  improvement  for  receiving  the 
strip  prepared  by  either  of  the  perforators  described  as  the  fifth  improvement, 
and  transmitting  voltaic  currents  along  the  telegraphic  conductor  to  the  receiv¬ 
ing  instrument  at  the  distant  station,  in  accordance  with  the  arrangement  of  the 


448 


MAGNETISM. 


perforations  in  the  paper  strip  (motion  being  produced  by  a  weight) ;  the  pro¬ 
pulsion  of  the  paper  strip  and  the  makings  of  the  contacts  with  the  batteries 
are  accomplished  by  the  same  power ;  and,  by  means  of  levers,  beam,  eccen¬ 
tric,  and  springs,  the  upper  ends  of  two  vertically  moving  pins,  being  alternately 
pressed  against  the  paper,  are  free  to  enter  the  perforations,  if  any  present 
themselves ;  or,  being  prevented  from  entering  the  paper  by  the  absence 
of  apertures,  they  regulate  the  succession,  frequency,  and  direction  of  the 
electric  currents  sent  into  the  telegraphic  circuit. 

The  action  of  the  pins  in  conjunction  witn  the  paper  strip  is  as  follows:  the 


F IG.  C. — Line  Printer  or  Receiver. 


only  means  of  propulsion  of  the  paper  is  by  the  pins  of  a  star-wheel  entering 
the  middle  perforations,  and  by  its  rotation  moving  the  paper  forward,  the 
strip  being  held  down  by  a  broad-toothed  wheel  pressing  it  against  the  paper- 
ledge,  the  vertically  moving  pins  entering  the  notches  in  the  before-mentioned 
wheel,  pass  through  an  aperture  in  the  paper,  and  are  carried  forward  by  it, 
thus  not  interfering  with  the  duration  of  contact  at  the  lower  end  of  the  pins; 
the  reacting  springs  restore  them  to  their  normal  position  on  their  downward 
movement,  effected  by  the  levers  to  which  they  are  attached  receiving  an 
up-and-down  motion  from  an  oscillating  beam,  connected  with  an  eccentric 
driven  by  the  maintaining  power  ;  and,  on  the  arrival  of  an  outer  aperture 
on  one  side  of  the  middle  line  of  holes,  the  pin  of  that  side  will  enter  and 
transmit  a  current  in  one  direction  ;  and  on  the  presentation  of  an  aperture  on 
the  opposite  side,  the  pin  will  also  enter  and  transmit  a  current  in  an  opposite 
direction,  the  apertures  in  the  paper  regulating  the  frequency,  direction,  and 
duration  of  the  current  sent  into  the  telegraph  line. 

In  the  Line  Printer  or  Receiver  (Fig.  C),the  magnetic  armatures  are  placed 
in  a  vertical  position;  the  central  axis  is  prolonged  so  as  to  carry  the  cross¬ 
piece,  through  an  aperture  in  the  extremity  of  which  a  horizontal  rod  passes ; 
on  this  is  mounted  at  one  extremity  the  small,  light  tracing-disc,  whilst  the 
opposite  end,  which  is  loosely  centred,  so  as  to  be  capable  of  a  slight  lateral 
movement,  carries  a  small  toothed  wheel;  this  wheel,  gearing  with  the  main- 


WHEA  TSTONE  'S  TELEGRAPHS. 


449 


taining  power  of  the  instrument,  imparts  a  rotatory  motion  to  the  tracer,  at 
the  same  time  that  the  axis  is  capable  of  receiving  a  to-and-fro  motion  in  a 
horizontal  plane  from  the  movement  of  the  armatures  and  arm. 

In  the  same  vertical  plane,  and  immediately  beneath  the  tracing-disc,  is  an 
inking-disc,  caused  to  rotate,  by  appropriate  gearing,  with  the  maintaining 
power  of  the  apparatus :  this  disc  revolves  in  a  reservoir  containing  ink  or 
other  suitable  marking  fluid.  The  periphery  of  the  disc  is  slightly  hollowed, 
and  the  edge  of  the  tracing-disc  just  enters  this  hollow  without  contact  or 
friction  with  the  inking-disc ;  during  the  revolution  of  the  disc,  capillary  at¬ 
traction  keeps  the  hollow  full  of  ink,  and  a  constant  and  uniform  quantity  will 
be  supplied  to  the  tracing-disc. 


Jl  B 


F IG.  D. —  The  various  parts  of  Apparatus  used  with  Wheatstone's 

Chronoscope. 


The  paper  intended  to  receive  the  marks  is  drawn  forward  at  suitable  speed 
over  a  roller  in  close  proximity  to  one  edge  of  the  tracing -disc.  It  will  be 
understood  that  a  series  of  instantaneous  alternate  currents  passing  through 
the  electro-magnet  causes  a  to-and-fro  motion  of  the  tracing-disc,  a  current  in 
one  direction  pressing  tit;  tracing-disc  against  the  paper,  where  it  will  remain, 
by  reason  of  the  residual  magnetism  of  the  electro-magnets  retaining  the 
armatures  in  that  position,  until  a  current  in  the  opposite  direction  withdraws 
the  tracer  from  the  paper.  By  this  arrangement  lines  of  more  than  two  lengths 
can  be  printed  with  perfect  accuracy  in  connection  with  the  perforator  with  five 
keys  described  as  the  fifth  improvement.  Another  remarkable  instrument  is 
Wheatstone's  Chronoscope.— The  various  parts  of  this  arrangement 
are  shown  at  Fig.  D,  and  employed  to  ascertain  the  velocity  of  projectiles. 
They  will  be  readily  understood  \yhen  we  describe  the  ball-holder  and  target 
used  in  the  falling  bodies  experiments,  a  and  B  are  enlarged  parts  of  screens; 


MAGNETISM. 


45° 


C  is  the  ball-holder  closed  to  receive  the  ball,  each  side  being  insulated.  The 
electric  circuit  is  not  complete;  but,  at  the  moment  of  the  release  of  the  ball, 
the  two  sides  will  meet  and  complete  the  circuit,  which,  traversing  in  one 
direction,  will  start  the  chronoscope:  this  will  continue  running  until  the  ball 
strikes  the  target,  when  it  will  reverse  the  current  and  stop  it.  The  method  of 
reversing  is  readily  understood  by  E  and  D,  Fig.  D.  Two  springs  are  fixed  to  the 
target,  which  is  hinged  at  one  end,  the  other  end  falling  when  the  ball  strikes 
it.  The  springs  slide  over  the  reversing-piece,  consisting  of  two  poles  of  the 
battery,  which  are  bridged  over  at  the  back,  as  indicated  by  the  dotted  lines,  E. 


Fig.  E. —  The  Chronoscope  in  Elevation. 


Fig.  E  represents  the  chronoscope  as  arranged  for  indicating  automatically 
the  time  occupied  by  falling  bodies.  A  is  a  column,  upon  which  the  ball-holder 
slides,  the  target  being  placed  at  the  base;  B  is  the  chronoscope,  consisting  of 
clockwork  mechanism,  with  two  dials,  one  divided  into  hundredths,  and  the 
other  into  thousandths,  of  a  second,  with  hands  like  a  watch,  motion  being  com¬ 
municated  to  it  by  a  weight  passing  over  a  pulley,  which  is  regulated  by  an  escape¬ 
ment  with  a  musical  spring,  tuned  to  a  thousandth  part  of  a  second,  caused  to 
sound  by  the  pressure  of  air  from  the  bellows,  C.  The  clockwork  is  in  two  dis¬ 
tinct  parts,  the  driving  and  the  dial  parts ;  they  are  made  to  gear  by  sensitive 
magnetic  needles  and  an  electro-magnet.  One  pole  of  the  battery  is  connected 
with  the  ball-holder,  the  other  with  the  target;  two  wires  from  the  target 
connect  it  with  the  chronoscope,  one  wire  connecting  the  ball-holder  with  the 
target.  The  poles  of  the  battery  are  so  arranged  that  on  the  release  of  the  ball 
the  electric  circuit  is  completed,  and  the  dials  are  brought  into  gear  with  the 
driving  part ;  the  current  is  reversed  the  instant  the  ball  strikes  the  target,  and 


WHEATSTONE’S  TELEGRAPHS. 


45i 


Fig.  F.  —  Wheatstone’s  Projectile  Arrangement. 

The  targets,  b  and  c,  connected  with  the  battery,  d,  and  '*  heafstone’s  chronoscope,  arranged  to 
receive  and  indicate  the  velocity  of  the  shot  from  the  Armstrong  gun,  a. 


the  dials  are  disengaged,  enabling  the  operator  to  read  off  the  time  by  the 
hands,  without  the  tedious  calculation  necessary  by  other  means  generally 
employed.  The  almost  inexhaustible  inventive  faculty  of  Wheatstone,  ever 
devising  new  or  improving  older  inventions,  is  again  displayed  in  his  New 
Telegraph  Thermometer  (Fig.  G). 

This  instrument  was  invented  by  Wheatstone  to  supply  a  scienific  want, 
viz.,  the  means  of  ascertaining,  day  or  night,  without  making  tedious  ascents, 
the  temperature  of  any  lofty  summit — such  as  that  of  Mont  Blanc. 

The  cut  (Fig.  G)  represents  the  general  internal  arrangement  of  the  instru¬ 
ments  requisite  to  ascertain  the  temperature  at  a  distant  point,  two  insulated 
wires  connect  them,  the  earth  being  used  to  form  the  third  conductor. 

The  apparatus  includes  the  thermometric  arrangement,  and  also  an  electro¬ 
magnetic  contrivance  for  converting  the  vibrations  of  magnetic  needles  between 
electro-magnets  into  a  circular  motion,  for  the  purpose  of  altering  the  electric 
conduction  from  one  circuit  to  ano‘her. 

In  order  to  indicate  the  temperature  measured  by  the  .nstrument  above 
mentioned,  t  lere  is  an  electro-magnetic  arrangement,  and  also  a  permanent 
compound  magnet  with  fixed  coils,  having  an  armature  opposite  to  its  poles, 
capable  of  being  rotated  by  a  handle,  to  produce  a  series  of  alternately  inverted 
currents. 

Fig.  g,  p.  419,  represents  the  internal  construction  of  both  instruments  ;  the 
dotted  and  other  lines  reoresent  the  wires  necessary  to  conduct  the  electric 
currents.  In  the  knob  A,  which  is  attached  to  the  glass  covering  the  dial,  is 
contained  a  metallic  thermometer,  having  a  hand  or  pointer  attached  to  its  axis; 
and  in  the  same  line  is  an  insulated  axle,  with  arms,  C  and  D,  proceeding  from  it, 
a  spiral  spring  tending  to  maintain  the  contact  of  the  arm  C  with  the  hand  B; 
under  this  axle  is  a  toothed  wheel,  F,  with  a  spring-catch,  E,  the  said  wheel 
gearing  with  the  pinion  G,  connected  by  a  spindle  with  the  wheel  H,  mounted 

20 — 2 


452 


MAGNETISM. 


on  an  oscillating  arm  proceeding  from  the  axle,  carrying  the  magnetic  needles 
placed  between  two  coils  (only  one  is  shown  in  the  drawing)  analogous  to  the 
indicator  of  the  alphabetical  telegraph  (Fig.  A).  O  K  is  a  similar  arrange¬ 
ment;  M  N  is  a  magnetic  machine. 

When  an  observation  is  about  to  be  made,  the  dial  of  the  indicator  is  ad¬ 
justed  to  zero  by  means  of  the  rim  P,  and  the  handle  N  rotated,  producing  a 
series  of  positive  and  negative  currents,  which  may  be  imagined  to  take  the 
course  indicated  by  the  arrows,  coming  from  a  coil,  passing  through  wire  6  to 


Fig.  g. 


! 

I 

i 


! 


the  coils  J,  the  short  wire  to  the  axle  C  D,  to  the  hand  B,  and  wire  7  to  the  coils 
of  the  magnets,  thus  completing  the  circuit,  causing  the  needles  between  the 
coils  j  to  oscillate  by  their  alternate  attraction  and  repulsion,  communicating 
that  motion  by  the  arm  H  j  to  the  wheel  H,  which,  by  its  peculiar  construction, 
will  rotate,  communicating  that  motion,  by  means  of  the  pinion  G,  to  the 
wheel  F  in  the  direction  G  E  D  ;  the  pin  E,  pressing  against  the  arm  D,  will  draw 
away  the  arm  C  from  the  hand  B;  the  piece  D  C  will  make  a  partial  rotation 
on  its  axis,  or  describe  an  arc  by  the  arms  C  D,  the  angle  being  the  number 
of  the  degrees  of  temperature,  thus  breaking  the  circuit  at  C  B,  and  completing 
it  through  D  E ;  the  wheel  F,  and  wire  8,  including  the  coils  K,  imparting  motion 
to  the  hand  or  pointer  o  by  the  same  means  to  those  already  described,  which 
will  continue  until  the  catch  F  arrives  at  the  pin  E,  corresponding  to  the  zero 
in  the  scale  of  the  instrument,  when  it  will  disengage  the  pin  E  from  arm  D, 
the  spiral  spring  forcing  arm  c  in  contact  with  the  hand  B,  thus  restoring  the 
circuits  to  their  former  condition. 

When  the  circuit  is  complete  through  the  wires  6  and  7,  only  the  coils  j 
come  into  action;  but  when  the  connections  are  made  through  wires  6  and  8, 
both  coils  are  caused  to  act.  moving  the  arm  c  in  the  thermometer  from  the 
highest  point  indicated  on  the  dial  to  the  zero,  and  in  the  indicator  from  the 
adjusted  zero  to  the  highest  point,  when  the  motion  of  the  pointer  will  cease, 
indicating  the  state  of  the  dial  n  A. 


WHEATSTONE’S  TEL  EG  K  A  TH S. 


453 


In  a  paper  read  by  Sir  Charles  Wheatstone  before  the  Academy  of  Sciences 
at  Paris  he  thus  sums  up  the  advantages  of  his  automatic  printing  telegraphic 
system : 

“  I  will  conclude  by  offering  a  few  remarks  on  the  advantages  possessed  by 

this  system. 

“  Whatever  practical  dexterity  may  be  acquired  by  a  voluntary  operator,  the 
result  arrived  at  will  be  far  inferior  to  that  obtained  by  the  automatic  process, 
which  is  only  limited  by  the  rapidity  with  which  the  recurring  motions  of  the 
transmitter  can  be  effected.  By  the  present  construction  of  the  instrument, 
five  times  the  quantity  of  signs  at  present  used  can  be  transmitted  to  mode¬ 
rate  distances ;  though  for  very  considerable  distances  this  rapidity  may  be 
limited  in  conductors  subjected  to  inductive  influences  by  the  tendency  which 
rapidly  recurring  short  currents  have  to  coalesce. 

“  But  even  if  there  were  no  advantage  in  point  of  rapidity  possessed  by  the 
automatic  over  the  voluntary  process  of  transmission,  its  other  advantages 
would  be  incontestable.  For  the  profitable  working  of  a  telegraphic  line,  it  is 
necessary  that  the  operator  should  manipulate  as  rapidly  as  is  consistent  with 
a  correct  transmission  of  the  message  :  it  requires  great  skill  to  become  a  pro¬ 
ficient  in  such  manipulations,  even  when  the  language  in  which  the  despatch 
is  sent  is  quite  familiar  to  the  operator ;  but  if  he  would  send  a  despatch  in  a 
language  unknown  to  him,  or  in  cipher,  he  is  obliged  to  proceed  with  caution 
and  slowness.  In  my  new  system  the  prepared  messages  are  transmitted  with 
equal  rapidity  in  whatever  language  or  cipher  they  may  be;  and  as  the  perfo¬ 
rated  bands  may  be  prepared  at  leisure,  and  be  subjected  even  to  the  revision 
of  a  corrector,  guarantees  of  accuracy  are  obtained  which  cannot  be  afforded 
by  the  system  of  immediate  voluntary  transmission.  Several  clerks  will  be 
required  to  prepare  messages  fora  single  telegraphic  line  in  constant  activity; 
but,  in  an  economical  point  of  view,  their  time  is  of  far  less  importance  than 
the  time  occupied  by  the  transmission  of  a  message. 

“Another  advantage  this  new  system  possesses  is  that  the  same  prepared 
message  may  be  transmitted  through  any  number  of  distinct  lines,  if  not 
simultaneously,  at  least  in  such  rapid  succession  as  to  be  equivalent  thereto; 
and  besides,  without  any  fresh  labour,  the  same  message  may  be  retransmitted, 
if  thought  necessary;  and  service  messages  in  constant  use  may  be  preserved 
for  transmission  whenever  they  may  be  required. 

“  Were  this  automatic  system  generally  adopted,  it  might  in  many  instances 
be  more  convenient  to  prepare  the  messages  at  the  offices  from  which  they  are 
'  sent,  the  instrument  for  effecting  this  purpose  being  very  portable  and  of  small 
cost.  The  operations  at  the  telegraph  office  would  in  these  cases  be  limited 
to  passing  the  perforated  band  through  the  transmitter  at  one  station  and  re¬ 
ceiving  the  printed  message  at  the  other,  the  translation  as  well  as  the  pre. 
paration  of  the  message  devolving  on  the  department  of  the  administration 
to  which  it  relates. 

“  In  the  present  case  it  is  not  the  question  to  substitute  one  kind  of  acquired 
ski*'  for  another  kind  equally  difficult  to  attain,  which  would  entail  great  labour 
or  H  ;he  employes.  The  great  practical  dexterity  at  present  required  being 
di  spensed  with,  and  the  principal  and  most  laborious  operation  being  entirely 
automatic,  there  is  little  to  learn,  though  there  may  be  something  to  forget  ” 


454 


MAGNETISM . 


THE  ATLANTIC  TELEGRAPH  CABLE. 

The  resistance  of  a  conductor  of  any  given  metal  is  directly  proportional 
to  its  length ,  and  inversely  proportional  to  its  thickness  or  cross  section. 

It  was  soon  found  to  be  necessary,  in  experiments  with  thousands  of  miles 
of  cable  or  insulated  wires,  to  adopt  some  standard  or  starting-point,  in  order 
to  ascertain  exactly  the  resistance  of  the  whole. 

The  matter  was  put  into  the  hands  of  a  committee  of  the  British  Associa¬ 
tion,  who  determined  that  an  English  mile  of  pure  copper  wire,  No.  1 6,  should 
be  the  B.  A.  unit ;  they  further  constructed  a  wire  of  silver  and  platinum, 
because  it  was  little  affected  by  temperature,  which  they  deposited  as  the 
standard  of  comparison,  and  this  length  of  wire  they  estimated  in  figures  to 
be  13*59  °f  the  length  of  the  copper  wire.  Bobbins  upon  which  hundreds  and 
thousands  of  miles  of  copper  wire  No.  16  would  have  to  be  wound  would  be 
too  bulky  and  cumbersome  to  manage ;  it  has,  therefore,  been  arranged  that 
German  silver,  an  alloy  of  about  60  parts  of  copper  with  a  fraction  of  lead, 
25  zinc,  and  r  5  nickel,  should  be  employed,  because  it  has  about  thirteen  times 
less  conducting  power  than  the  same-sized  copper  wire ;  consequently  the 
standard  unit  would  be  represented  as  follows : 

B.  A.  unit  of  German  silver  wire=  13*59  of  an  English  mile. 

The  bobbins,  having  13*590!  an  English  mile  of  German  silver  wire  wound 
upon  them,  represent,  therefore,  a  resistance  equal  to  one  mile. 

The  length  of  the  great  Atlantic  cable,  stretching  between  Valentia  in  Ire¬ 
land  and  Newfoundland  in  America,  a  distance  of  3,500  miles,  is  1,858  knots, 
and  each  knot,  equal  to  ~]\  nautical  miles,  has  an  electrical  resistance,  at  a 
temperature  of  75"  Fahrenheit,  equal  to  4*272  of  the  above-named  B.  A.  units. 
Consequently  1,858  knots,  multiplied  by  4*272,  would  give  the  resistance  of  the 
whole  cable  as  7,937  B.  A.  units  ;  or,  allowing  for  diminished  resistance  caused 
by  the  low  temperature  of  the  bed  of  the  Atlantic,  and  deducting  a  certain 
number  of  units  for  that,  we  have,  say,  7,500  B.  A.  units. 

The  resistance  of  the  cable  of  1865,  according  to  Mr.  Latimer  Clark,  is 
7.604  B.  A.  units.  The  resistance  of  the  last  new  cable,  1866,  is  7,209  B.  A. 
units.  It  is  so  much  better,  and  the  instruments  are  so  vastly  improved,  that 
they  can  send  from  eighteen  to  twenty  words  per  minute,  instead  of,  as  formerly, 
only  two  and  a  half.  The  new  cable  has  three  times  more  speaking  power 
now  it  is  immersed  in  the  Atlantic  than  it  had  on  board  the  Great  Eastern. 

At  the  commencement  of  the  article  on  Electricity,  great  stress  was  laid 
upon  the  explanation  of  the  phenomena  of  induction.  The  conducting  wires 
of  the  Atlantic  cable,  formed  of  a  strand  of  seven  wires,  each  0*048  inch  in 
diameter,  an  J  together  equal  to  a  wire  of  0*144  inch  diameter,  are  surrounded 
with,  and  insulated  by,  gutta-percha. 

Such  being  the  case,  it  is  easy  to  understand  that,  when  conveying  an  elec¬ 
trical  current,  it  must  become  charged  like  a  Leyden  jar.  The  wire  is  the  inner 
metallic  coating,  the  gutta-percha  is  equivalent  to  the  glass,  and  the  salt  water 
outside  the  other  metallic  coating.  This  enormous  Leyden  jar  measures  in  its 
inner  coating  about  425,000  square  feet,  and  it  was  the  charge  maintained  by 
the  cable  that  seemed  at  first  to  negative  and  destroy  all  hope  of  sending 
messages  quickly.  This  very  property  is  now  found  to  be  most  valuable,  and 


THE  ATLANTIC  CABLE. 


455 


Fig.  394. —  Thompson's  Reflecting  Galvanometer  Needle. 

C,  The  galvanomtter;  D,  the  oxy-hydrogen  light;  E  e,  the  scale;  w  w  vv  \v,  the  Wheatstone  bridge 
F,the  key  ;  G,  ext’a-resistance  coils;  and  h,  the  battery. 


is  made  use  of  to  expedite  the  sending  of  the  signals,  and  in  brief  terms  may 
be  thus  described : 

The  cable  is  first  charged  until,  like  a  Leyden  jar,  it  will  bear  no  more.  In 
order  to  send  a  message,  it  is  discharged ;  and  it  is  the  latter  operation,  acting 
upon  instruments  of  wondrous  delicacy,  that  enables  the  operator  to  send  the 

message.  . 

Sir  William  Thompson’s  reflecting  galvanometer  needle  is  a  notable  illus¬ 
tration  of  the  perfection  to  which  a  galvanometer  may  be  brought;  and  his 
original  instrument  has  been  surpassed  and  brought  up  to  a  still  highei  pitch 
of  refinement  by  Mr.  Becker,  the  learned  and  obliging  head  of  the  instrument 
department  at  Messrs.  Elliott’s.  The  writer  understood  him  to  say  that  he 
was  making  one  to  show  a  resistance  of  one  in  a  million  units. 

Mr.  Becker  arranged  a  most  excellent  series  of  instruments  for  demonstra¬ 
ting  at  the  Polytechnic.  The  Thompson’s  reflecting  galvanometer  needle  with 
Wheatstone’s  bridge  are  shown  above  (Fig.  394)?  as  exhibited  at  the  above- 
named  institution  by  the  writer. 

The  reflecting  galvanometer  needle  must  first  engage  our  attention.  It  con¬ 
sists  of  two  large  flat  bobbins,  B  B  (Fig.  395)*  uPon  which  are  wound  many 
hundred  yards  of  insulated  fine  copper  wire,  and,  in  the  instrument  made  for  the 
writer,  they  were  placed  on  hinges,  so  that  they  could  be  placed  down,  like  the 
lid  of  a  box,  to  disclose  the  delicate  needle — a  small  magnet,  a,  made  of  watch- 
spring  about  an  inch  long,  and  weighing  only  a  few  grains,  and  hung  by  a  very 
narrow  piece  of  tape;  because  a  filament  of  silk,  if  made  the  suspender,  would 
have  caused  the  instrument  to  be  too  delicate  for  lecture-room  purposes. 


456 


MAGNETISM. 


Fastened  to  the  little 
magnet  is  a  circular  mir¬ 
ror,  ground  slightly  con¬ 
cave,  and  weighing  only 
a  few  grains  ;  upon  this 
is  thrown  from  an  aper¬ 
ture  in  a  copper  lantern 
a  few  rays -from  the  oxy- 
hydrogen  light.  These 
are  reflected  upon  a  scale 
of  5  ft.  6  in.  in  length,  so 
that  the  spot  of  light  when 
it  traversed  the  scale  could 
be  seen  by  an  audience  of 
one  thousand  people. 

Mr.  Latimer  Clark  has 
improved  the  Thompson 
Reflecting  Lecture  Galva¬ 
nometer  for  public  de¬ 
monstration  ;  and  instead 
of  showing  the  movement 
of  the  spot  of  light  over 
a  length  of  6  ft.,  has  in¬ 
creased  it  to  20  or  more 
feet,  and  has  attached  a 
thermo  -  electric  control¬ 
ling  battery  for  checking 
and  steadying  the  move¬ 
ment  of  the  magic  lantern 
image  of  an  arrow  which 
moves  on  the  scale  of  20 
or  more  feet  in  length. 

The  movements  of  the  spot  of  light  are,  of  course,  those  of  the  magnet,  and 
in  order  that  the  latter  should  be  acted  upon  only  by  the  currents  sent  through 
the  instrument,  and  not  by  terrestrial  magnetism,  a  curved  steel  magnet,  work¬ 
ing  up  or  down  or  right  and  left,  or  a  brass  rod,  is  placed  above  it,  and  is 
most  convenient  for  keepingthe  axis  of  the  little  mirror  A,  with  its  attached  mag¬ 
net,  exactly  between  and  parallel  with  the  two  bobbins  B  B,  or,  in  other  words, 
reflecting  the  spot  of  light  to  zero.  C  and  D  represent  the  connecting  screws. 

But,  perfect  as  this  galvanometer  is,  it  would  not  have  enabled  the  writer  to 
teach  others  much  about  resistances  and  other  interesting  points  connected 
with  the  Atlantic  Telegraph  cable,  unless  he  had  used  an  instrument  for  which 
sufficient  credit  has  not  been  given  to  its  distinguished  inventor,  Wheatstone, 
viz. 

The  Differential  Resistance  Measurer. 

This  instrument  (better  known  by  the  name  of  Wheatstone’s  Bridge)  was 
also  constructed  by  Mr.  Becker  on  the  largest  scale  (Fig.  394).  The  board  is 
8  ft.  long  and  2  ft.  8  in.  wide;  the  lozenge-shaped  brass  plates  are  1^  in.  wide. 
There  are  four  breaks  with  binding-screws,  and,  by  using  bobbins  upon  which 
the  B.  A.  unit  of  German  silver  wire  was  wound,  the  audience  was  made  to 
understand  that  each  bobbin  represented  a  mile  of  pure  copper  wire,  No.  16. 


B 


Fig.  395. —  Thompson's  Reflecting  Galvanometer 
Needle,  with  the  Bobbins  opened  to  show  the 
suspended  Needle. 


THE  ATLANTIC  CABLE.  457 


Fig.  396.— Diagram  I. 


In  the  lecture-room,  the  resistance  of  two  miles,  as  compared  with  one  mile, 
of  wire  was  clearly  demonstrated.  The  resistance  of  two  equal  pieces  of 
wire  was  shown  to  be  altered  by  heat,  obtained  by  merely  touching  one  with 
the  hand  or  putting  it  into  the  mouth. 

Three  tubs  of  water,  containing  three  lengths  of  wire,  measuring  one  hun¬ 
dred  yards,  were  supposed  to  represent  the  Atlantic  Telegraph  Cable,  and 
were  balanced  against  a  resistance  coil.  Directly  the  miniature  cable  was 
broken,  the  spot  of  light  became  violently  agitated  when  the  key  was  pressed 
down;  and  it  was  shown  that,  time  permitting,  the  lecturer  could  discover  not 
only  that  the  wire  was  broken,  but  where  it  was  broken — just  as  they  can  now 
discover  any  place  thousands  of  miles  from  England,  and  deep  down  in  tne  bed 
of  the  Atlantic  Ocean,  where  an  accident  may  have  happened  to  the  cable ; 
they  can  determine  the  precise  spot,  and,  by  sending  a  proper  vessel  with 
tackle,  can  pick  up  and  reunite  and  repair  the  broken  part,  as  they  did  in  the 
recovery  and  resplicing  of  the  old  Atlantic  Telegraph  Cable. 

The  Differential  Resistance  Measurer  is  fully  described  by  Wheatstone  in 
the  “Transactions  of  the  Royal  Society,”  1843,  Part  II.,  p.  323. 

For  the  sake  of  the  young  student,  and  considering  also  that  the  construc¬ 
tion  and  principle  of  Wheatstone’s  bridge  frequently  form  the  subject  of  an 
examination  question,  the  writer  gives  the  following  diagrams  and  explana¬ 
tions,  which  he  trusts  will  be  found  useful. 

For  the  sake  of  simplicity,  the  brass  bands  and  breaks  only  are  shown. 

The  galvanometer  is  supposed  to  be  resting  in  the  middle  of  the  board,  the 
battery  on  the  right,  and  the  connecting  key  on  the  left. 

0 


For  the  sake  of  discussion,  it  is  supposed  that  the  current  coming  from  the 
battery,  B  a,  is  represented  by  twelve  parts:  these,  on  arriving  at  P,  split  or 
divide  into  equal  parts ;  six  go  in  the  direction  a',  and  six  in  the  other.  A. 


458 


MAGNETISM. 


Q 


Fig.  397— Diagram  II. 


The  two  currents,  represented  by  arrows,  both  pass  through  equal  resistance 
coils,  A'  A,  and  the  respective  currents  might  pass  direct  to  the  key  K  (where 
contact  is  made  or  broken),  and  through  that  to  the  other  pole  of  the  battery ; 
but  the  currents  are  partially  arrested  by  the  equal  resistance  coils,  B'  B,  and 
a  portion  of  the  currents  is  forced  into  or  diverted  into  the  galvanometer,  G  N. 

I  he  use  of  the  coils,  or  any  other  resisting  matter,  on  the  other  side  of  the 
galvanometer  is  to  force,  or  rather  gently  to  impel,  a  part  of  the  current  into 
the  galvanometer;  because,  if  this  was  not  done,  the  deflection  would  be  sc 
small  it  might  be  barely  perceptible. 

Let  us  say,  for  the  sake  of  discussion,  that  two  parts  pass  to  the  gaivano 


THE  ATLANTIC  CABLE. 


459 


meter  from  Q,  and  two  parts  from  S;  such  currents,  coming  in  opposite  direc¬ 
tions,  must  oppose  each  other’s  progress  through  the  galvanometer,  and  there¬ 
fore  the  needle  of  the  latter  does  not  move. 

We  have  only  now  to  suppose  that  4  +  2=6  proceed  from  Q'  to  R,  and 
4  +  2  =  6  by  S  to  R;  the  two  added  together  make  12,  the  original  quantity 
started  with,  which  proceeds  through  the  key  and  connecting  wire  to  the  other 
pole  of  the  battery,  B  a. 

The  second  diagram  (Fig.  397)  consists  of  two  parts,  viz..  Part  I.  and  Part  1 1., 
and  it  is  recommended  that  the  latter  be  traced  on  tracing-paper  by  the  stu¬ 
dent,  who  can  place  it  upon  Part  I.  The  current  again  is  represented  by 
twelve  parts.  The  resistance  of  the  coil  at  a',  Part  I.,  being  less  than  A,  Part 
II.,  the  greater  part  of  the  current,  say  8  a' parts,  go  through  the  former,  and 
4  A  through  the  latter,  consisting  of  a  piece  of  copper  wire  and  a  resistance 
coil ;  therefore,  returning  to  Part  I.,  the  current  going  by  a',  through  q',  to  G  N, 
the  galvanometer  needle,  forms  at  the  point  Q  a  greater  partial  current  (say 
three  parts)  than  the  current  going  by  A,  Part  II.,  which  divides  at  S,  and  is 
represented  by,  say,  one  and  a  half  parts ;  therefore,  the  current  that  deflects 
the  galvanometer  is  the  greater  current  going  by  Q',  Part  I.,  and  marked  3; 
consequently  it  amounts  in  imagination  to  a  struggle  between  the  current  going 
by  q',  Part  I.,  represented  by  three  parts,  and  the  current  going  by  S,  Part  II., 
or  one  and  a  half  parts.  The  issue  cannot  be  doubtful ;  the  greater  current, 
three,  overcomes  the  lesser,  one  and  a  half.  In  Part  I.,  4  +  3  =  7  go  by  B;  and 
in  Part  II.,  five  go  by  B ;  and,  if  the  two  are  added  together,  they  again  make 
the  twelve  parts,  which,  as  before,  travel  through  the  key  and  connecting  wire 
to  the  other  pole  of  the  battery,  B  a. 


Q 


460 


MAGNETISM. 


the  same  wire.  The  lower  part,  A  B,  of  the  bridge,  marked  in  dotted  lines, 
is  not  required,  its  place  being  filled  by  a  long  German  silver  wire  stretched 
from  P  to  R,  and  provided  with  a  scale  divided,  say,  into  twenty  parts ;  on  this 
wire  slides  a  clip  or  binding-screw,  s,  and  this  is  connected  with  one  of  the 
galvanometer-screws,  the  other  screw  of  the  galvanometer  being  connected 
with  Q. 

In  this  case,  we  are  to  suppose  it  is  being  used  to  ascertain  the  relative 
lengths  of  wire  of  the  same  metal,  diameter,  and  conductivity.  The  clip,  s, 
has  been  moved  from  the  centre,  C,  to  No.  I3’334  on  the  scale  painted  below 
the  wire,  P  R.  The  clip  has  been  moved  to  1 3‘334,  or  until  the  galvanometer 
is  at  rest;  this  quantity,  I3'334,  is  double  that  of  R  S,  therefore  the  resistance 
at  b'  is  shown  to  be  half  the  resistance  at  a',  because  a'  has  two  coils,  or  two 
miles  of  wire,  and  b'  one  mile;  so  that  it  is  shown,  without  any  previous  know¬ 
ledge  of  the  absolute  length  of  the  two  coils  at  A  (the  wire  under  examination), 
that  it  is  double  the  length  of  the  known  quantity,  one  mile  at  B',  because  the 
scale  from  R  to  S  is  6‘666,  and  that  from  p  to  S  I3‘334,  and,  if  one  is  added  to 
the  other,  thev  make  up  the  whole  scale  of  20. 


The  object  of  the  diagram  (Fig.  399)  is  to  explain  the  use  of  the  arrange¬ 
ment  (Fig.  398,  Diagram  III.),  for  the  purpose  of  discovering  the  exact  point 
under  the  Atlantic  Ocean  where  the  cable  is  supposed  to  be  broken.  As  before, 
the  lower  part  of  the  bridge  is  not  used  :  the  wire,  P  R,  and  scale  are  employed 
in  this  experiment. 

The  current,  starting  from  the  battery  B  a ,  arrives  at  P,  where  it  splits  into 
two  currents :  one  passes  along  the  wire,  P  R,  and  the  other  is  supposed  to  go 
through  the  cable  marked  “Cable,”  at  A.  The  galvanometer  needle  is  brought 
to  rest  by  the  balancing  of  the  resistance  of  the  cable  by  various  resistance 
coils,  R  c,  at  B'  :  this  supposes  the  cable  to  be  perfect  when  the  clip,  S,  is  in 
the  centre. 

Let  us  now  imagine  that  the  cable  is  broken  at  X.  The  spot  of  light  from 
Thompson’s  galvanometer  needle  (see  Fig.  394,  p.  414)  is  now  violently 
agitated  or  deflected  when  the  contact  is  made  with  the  battery,  because  the 
current,  instead  of  travelling  through  the  whole  length  of  the  cable,  takes  a 


THE  ATLANTIC  CABLE. 


461 


short  cut,  as  shown  by  the  short  arrows ;  its  path  or  resistance  is  decreased 
enormously,  and  it  no  longer  balances  with  the  resistance  coils,  R  C,  at  B'.  To 
make  it  balance,  the  clip,  S,  is  moved  to  V;  then  by  measuring  the  distance 
from  R  to  Y,  and  the  distance  from  P  to  Y,  on  the  graduated  scale,  it  is  easy  by 
a  calculation  to  discover  the  distance  from  the  shore  where  the  rupture  has 
taken  place.  V  is  supposed  to  be  Valentia,  and  N,  Newfoundland  ;  E  and  E 
are  the  wires  which  go  out  into  the  sea,  and  are  usually  designated  as  “  earth- 
plates  ”  in  all  diagrams,  to  prevent  confusion. 


Fig.  400. — Diagram  V. 


The  last  diagram  (Fig.  400)  is  intended  to  give  the  student  a  general  notion 
of  the  apparatus  required  to  send  the  electric  current,  i.e.,  “  messages,”  through 
the  great  Atlantic  Telegraph  cable. 

We  commence  at  v,  Valentia.  B  a  is  the  battery  connected  with  the  earth- 
plate,  e';  k  is  the  key  connected  with  the  other  pole  of  the  battery  at  a;  E'  is 
the  earth-plate  (not  really  so,  as  it  is  a  wire  running  into  the  sea);  w  \V  repre¬ 
sents  the  cable  under  the  water,  passing  across  to  N,  Newfoundland,  where  the 
electric  force  enters  the  condenser,  C  (an  arrangement  of  mica  plates  and  tin- 
foil,  fulfilling  the  same  office  as  a  Leyden  battery),  through  the  galvanometer, 
G;  r  c  is  a  large  resistance  coil  connected  with  the  earth-plate  and  also  with 
the  cable  at  the  point  o  :  one  side  of  the  condenser  is  also  connected  w  h  the 
earth-plate. 

The  course  of  the  electric  force  is  certainly  tortuous,  but,  once  studied  and 
understood,  is  one  of  the  most  simp’e  and  beautiful  processes  of  reasoning 
that  the  lover  of  science  can  desire. 

As  the  cable  is  now  represented  in  the  diagram,  a  current  can  pass  from  the 
battery,  b  a,  through  K,  at  the  point  <7,  to  the  cable,  and  through  it  to  the  point 
o,  where  the  greater  part  will  pass  through  G,  the  galvanometer,  into  the  con¬ 
denser,  C;  the  other  part  of  the  current  passing  from  O,  through  the  resistance 


462 


MAGNETISM. 


coil,  R  c,  to  the  earth-plate  e',  and  from  E'  back  to  the  batter)'  B  a,  through 
the  other  earth-plate,  e'. 

The  current,  in  passing  through  the  galvanometer,  deflects  it  until  it  has 
fully  charged  the  condenser,  when  it  returns  to  zero. 

The  signals  are  sent  by  pressing  down  the  key,  K,  and  so  putting  the  cable 
to  earth  as  the  key  is  pressed  down  upon  b ,  which  is  connected  with  the  earth- 
plate  e'.  The  consequence  is  that  the  electrical  tension  of  the  cable  falls  below 
that  of  the  condenser;  a  current  then  flows  from  the  condenser,  C,  through 
the  galvanometer,  G  (deflecting  it,  the  deflection  being  the  signal),  to  the 
cable,  in  order  to  establish  the  equilibrium  of  the  latter. 

At  a  banquet  given,  at  the  Polytechnic,  by  the  chairman  and  directors  of  the 
Royal  Polytechnic  to  Sir  Charles  Wheatstone  and  the  scientific  men  of  Lon¬ 
don,  at  which  many  noblemen  and  gentlemen  assisted,  the  writer  was  enabled, 
by  the  kindness  of  the  various  telegraphic  companies,  to  bring  the  wires  into 
the  Polytechnic  ;  and,  whilst  the  company  were  seated,  the  follow’ing  message 
was  sent  to  the  President  of  the  United  States,  and  his  answer  received,  as  re¬ 
printed  in  “The  Evening  Post,”  New  York,  Wednesday,  January  1,  1868: 

“  Cable  News. — Advices  from  Europe  to  December  30,  1867. — The  follow¬ 
ing  advices  by  the  Atlantic  Telegraph  have  been  received : 

“international  courtesies. 

“  London,  December  24. — At  a  banquet  given  at  the  Royal  Polytechnic  on 
Saturday  night  last,  in  reply  to  the  following  sentiment  from  the  Duke  of 
Wellington  and  Sir  Charles  Wheatstone,  a  despatch  from  the  President  of  the 
United  States  was  read  amid  great  enthusiasm.  Not  a  little  of  the  interest 
attaching  to  these  despatches  grows  out  of  their  rapid  transmission : 

“MESSAGE  OF  THE  DUKE  OF  WELLINGTON  TO  THE  PRESIDENT  OF 

THE  UNITED  STATES. 

11 ‘■Royal  Polytechnic ,  London ,  December  21. — The  Duke  of  Wellington,  the 
directors  and  scientific  guests  now  at  the  Royal  Polytechnic,  London,  Eng¬ 
land,  send  their  most  respectful  greeting  to  the  President  of  the  United  States, 
their  apology  being  that  to  the  discoveries  of  science  the  intercourse  between 
two  great  nations  is  indebted.’ 

“  [The  above  message  was  9  minutes  30  seconds  in  transit  from  London  to 
Washington,  as  follows:  London  to  Heart’s  Content,  4  minutes  30  seconds; 
Heart’s  Content  to  Plaister  Cove,  1  minute  30  seconds;  at  Plaister  Cove,  30 
seconds;  Plaister  Cove  to  New  York,  1  minute  30  seconds;  New  York  to 
Washington,  1  minute  30  seconds.] 

“  REPLY. 

“  ‘  Washington ,  December  21. 

“  ‘  D nice  of  Wellington,  London:  I  reciprocate  the  friendly  salutation  of  the 
banqueting  party  at  the  Royal  Polytechnic,  and  cordially  agree  with  them  in 
the  sentiment  that  free  and  quick  communication  between  governments  and 
nations  is  an  important  agent  in  preserving  peace  and  good  understanding 
throughout  the  world,  and  advancing  all  the  interests  of  civilization. 

“‘Andrew  Johnson.’ 

“  The  reply  occupied  29  minutes  in  actual  transmission.  On  the  same 
evening,  a  message  of  twenty-two  words  was  started  from  the  Polytechnic 
for  Heart’s  Content  at  exactly  9  p.m.,  and  at  9.10  the  reply  of  twenty-four 
words  was  delivered.” 


THE  TELEPHONE. 


463 


The  Telephone, or  Talking  Telegraph,  of  Professor  Bell,  of  Boston,  U.S.A., 
has  given  quite  a  new  impetus  to  the  art  of  telegraphing,  which  bids  fair  to 
eclipse  all  previous  modes  of  annihilating  time  and  space,  and  is  thus  de¬ 
scribed  in  an  article 

On  Telephony. 

The  “  Daily  Telegraph,”  after  referring  to  the  manipulation  of  electricity, 
&c.,  says : 

“  Even  these  interesting  applications  of  electro-magnetism  have  recently 
been  eclipsed.  The  same  astounding  force  is  now  employed  not  only  in  the 
transmission  of  visible  symbols,  but  also  of  sounds  ;  and  some  enthusiasts 
confidently  announce  -  whether  on  sufficient  grounds  we  do  not  presume  to 
assert— that  telephony  is  destined  to  supersede  telegraphy.  By  a  coincidence 
which  has  sometimes  occurred  in  other  departments  of  scientific  exploration, 
there  are  simultaneously  two  explorers  in  the  telephonic  field,  both  of  whom, 
after  having  been  hard  at  work  on  the  new  invention  for  several  years,  have 
at  length  succeeded  in  demonstrating  that  it  is  practicable.  Professor  A. 
Graham  Bell,  of  the  Boston  University,  has  constructed  a  telephone  on  one 
principle,  and  Mr.  Elisha  P.  Gray,  of  Chicago,  another  on  a  different  system ; 
and  though  it  may  be  impossible  at  present  to  forecast  all  the  specific  pur¬ 
poses  to  which  the  invention  is  capable  of  being  applied,  extensive  scope  is 
certain  to  be  found  for  its  use. 

‘  The  earliest  attempt  to  transmit  sound  by  electricity  was  made  by  Reiss  in 
1861,  and  the  improvements  effected  in  the  same  direction  since  that  period 
are  reported  to  be  more  remarkable  than  those  which  distinguished  the  results 
accomplished  by  Wheatstone  and  Morse  in  telegraphy,  as  compared  with  the 
crude  experiments  of  Le  Sage  sixty-three  years  previously.  It  may,  therefore, 
be  inferred  that,  as  the  principle  of  telephony  is  now  scientifically  compre¬ 
hended,  the  perfecting  of  the  apparatus  is  only  a  question  of  time  and  labour. 

Professor  Bell  successfully  demonstrated  his  svstem  for  the  first  time  six 
months  ago  on  a  wire  extending  from  Boston  to  Cimbridge,  over  a  distance 
of  two  miles,  when  the  words  articulated  by  the  operator  at  the  latter  place 
could  be  distinctly  heard  at  the  former,  and  vice  versd,  the  dialogue  being 
conducted  in  the  ordinary  vocal  tones.  More  recently  a  bolder  experiment 
was  made  upon  a  w  ire  eighteen  miles  long,  between  Boston  and  Salem  ;  and 
in  January  last  Professor  Bell  had  brought  his  instrument  to  so  sensitive  a 
pitch  that  he  was  able  to  transmit  the  inflections  of  the  human  voice.  The 
well-known  song,  ‘The  Last  Rose  of  Summer,’  was  so  exactly  rendered  that 
not  a  single  note  was  lost  or  confused  in  the  passage.  The  sounds  communi¬ 
cated  are  described  to  have  been  as  clear  as  if  the  listener  were  ‘at  the  rear 
of  a  concert  hall,  a  hundred  feet  from  the  singer.’  Laughter,  applause,  and 
instrumental  music  were  subsequently  transmitted,  and  the  sounds  are  said 
to  have  been  so  minutely  exact  that  ‘a  violin  could  be  distinguished  from  a 
violoncello.’ 

“  The  maximum  distance  hitherto  bridged  by  Professor  Bell  is  one  hundred 
and  forty-three  miles,  and  the  instrument  rapidly  attains  a  higher  state  of 
efficiency.  The  report  of  a  lecture  was,  for  the  first  time,  dispatched  by  this 
same  process  from  Salem  to  Boston  On  that  occasion  speeches  were  sent 
from  the  latter  to  the  former  city,  and  the  applause  with  which  they  were 
greeted  in  Salem  was  distinctly  heard  in  Boston  The  experts  of  that  city  are 
now  addressing  themselves  to  the  more  serious  task  of  talking  through  wires 


MAGNETISM. 


464 


of  collective  diameter  corresponding  to  that  of  an  average  ocean  cable  ;  and, 
though  certain  obstacles  have  yet  to  be  surmounted  before  vocal  inflections 
can  be  transmitted  across  the  Atlantic  through  so  thick  a  medium,  the  fullest 
confidence  is  entertained  that  these  difficulties  will  be  entirely  overcome 

“  The  mechanism  of  Professor  Bell’s  apparatus  consists  of  a  powerful  com¬ 
pound  permanent  magnet,  to  the  poles  of  which  are  attached  ordinary  tele¬ 
graph  coils  of  insulated  wire.  In  front  of  the  poles  is  a  diaphragm  of  iron, 
and  a  mouthpiece  whose  function  is  to  converge  the  sound  upon  this  diaphragm. 
When  the  human  voice  causes  the  diaphragm  to  vibrate,  electrical  undula¬ 
tions  are  induced  in  the  coils  around  the  magnets  precisely  similar  to  the 
undulations  produced  by  the  human  voice.  These  coils  are  connected  with 
the  line  wire,  and  the  undulations  caused  in  them  travel  through  the  wire,  and 
passing  through  another  instrument  at  the  opposite  terminus  of  the  line,  are 
again  resolved  into  atmospheric  undulations  by  a  metallic  diaphragm  similar 
to  the  one  already  described.  Mr.  Gray’s  instrument  is  not  constructed  for 
the  purpose  of  conveying  promiscuous  sounds,  as  in  the  former  case.  It  is, 
on  the  contrary,  represented  as  a  ‘  telephonic  piano,’  and  itself  produces  the 
sounds  which  it  transmits.  It  has  already  been  tested  on  a  wire  uniting 
Chicago  and  Milwaukee,  distant  about  eighty-five  miles,  and  several  airs  per¬ 
formed  in  the  latter  city  were  distinctly  recognizable  by  the  audience  assembled 
in  the  former,  and  the  performance  elicited  rapturous  applause.  Since  that 
trial,  a  distance  of  two  hundred  and  eighty-four  miles,  between  Chicago  and 
Detroit,  lias  been  achieved,  and  that  experiment  is  said  to  have  been  entirely 
successful.  A  transmitter  and  a  receiver  constitute  Mr.  Gray’s  principal 
apparatus.  The  first  of  these  consists  of  a  keyboard  of  two  octaves,  and  a 
tuning- bar,  an  electro-magnet,  and  electric  circuit.  Vibratory  molecular 
action  is  communicated  to  the  iron  by  magnetization  when  the  keys  of  the 
instrument  are  struck.  The  receiver  at  the  other  end  of  the  line  consists  of  a 
:arge  ‘  sounding-box,’  on  which  is  mounted  an  electro-magnet. 

“  Obviously,  however,  the  invention  of  Professor  Bell  is  susceptible  of  the 
greater  variety  of  uses.  Still,  for  the  purpose  of  journalistic  reporting,  the 
balance  of  advantage  appeals  for  the  present  to  lie  with  ordinary  telegraphy. 
Apart  from  private  telegraphic  communication,  occasions  may  sometimes 
arise  when  the  heart  of  the  country  throws  under  a  great  common  impulse, 
and  when  the  inhabitants  of  Birmingham,  Manchester,  and  Glasgow  might 
be  unusually  anxious  to  become  immediately  acquainted  with  the  proceedings 
of  a  public  meeting  held  in  the  metropolis.  In  that  case  gatherings  might 
assemble  in  those  towns  and  listen  at  one  time  to  the  speeches  as  they  were 
being  delivered  at  St.  James’s  or  Exeter  Hall.” 


THE  TELEPHONE. 

At  the  conversazione  of  the  Society  of  Telegraph  Engineers,  held  a  short 
time  since,  a  Telephone,  differing  in  some  material  respects  from  those  pre¬ 
viously  made,  was  exhibited  by  the  Messrs.  Wray. 

Like  all  other  instruments  of  this  class,  it  consists  of  two  parts,  viz.,  a  trans¬ 
mitter  and  a  receiver.  The  transmitting  instrument  differs  from  that  of  Reiss 
in  being  provided  with  an  inner  membrane,  B,  so  placed  as  to  protect  the 
outer  or  transmitting  membrane,  C,  from  the  action  of  the  breath,  and  other 
disturbing  influences,  and  also  to  modify  its  vibrations. 


THE  TELEPHONE. 


465 


By  Fig.  T  it  will  be  seen  that  the  instrument  consists  of  a  rectangular  box, 
having  a  gable-shaped  top,  one-half  of  which  is  open,  while  the  other  is 
covered  by  a  piece  of  wood  having  a  large  circular  hole,  into  which  is  fitted 
the  drumhead,  C,  formed  of  thin  india-rubber. 


Fig.  t. —  The  Transmitter. 


In  the  centre  of  this  drumhead  a  small  disc  of  platinum  foil  is  affixed,  and 
is  connected  with  the  binding-screw,  F.,  by  means  of  two  fine  copper  wires, 
which  dip  into  the  small  mercury  cups,  F  F.  By  this  arrangement  the  mem¬ 
brane  is  quite  free,  and  consequently  will  vibiate  to  high  or  to  feeble  notes. 

To  the  lever,  G,  a  platinum  wire  is  attached  so  as  to  almost  touch  the  centre 

X> 


466 


MAGNETISM. 


of  the  metal  disc,  and  is  adjusted  by  the  screw,  H,  through  the  medium  of  the 
lever,  I.  The  binding-screw,  J,  is  connecced  with  the  lever,  G,  through  the 
spring,  K. 

Fig.  U  represents  the  receiver :  L  L  are  bobbins  filled  with  fine  wire  ;  in 
the  centre  of  each  helix  is  a  light  bar  of  soft  iron,  which,  as  they  do  not  touch 
the  bobbins,  can  vibrate  freely.  The  outer  ends  of  the  bars  are  soldered  to 
pieces  of  flat  bars,  held  in  position  by  the  screws,  M  M  ;  while  their  inner 
ends  are  placed  so  as  to  be  almost  in  contact  with  each  other.  N  N  are 
binding-screws  to  which  the  ends  of  the  coils,  L  L,  are  attached.  The  coils 
are  so  wound  that  they  impart  to  the  inner  ends  of  the  soft  iron  bars  opposite 
polarity. 


Fig.  u. —  The  Receiver. 


o  is  a  box  made  of  thin  A'ood,  in  the  top  of  which  (directly  under  the 
inner  ends  of  the  electro-magnets)  is  a  sound -hole  ;  and  inside  the  box, 
near  this  hole,  is  a  sound-post.  The  sounding-box  so  constructed,  while 
serving  the  purpose  of  a  stand,  also  very  materially  increases  the  tones 
emitted  by  the  electro-magnets. 

When  a  note  is  sung  into  the  opening,  A,  of  the  transmitter,  it  causes  the 
membrane  to  vibrate  ;  this,  in  its  turn,  communicates  the  vibrations  to  the 
drumhead,  c. 

If  the  note  sounded  is  the  bass  C,  the  drumhead  will  vibrate  128  times  per 
second,  and  will  cause  the  platinum  disc  to  form  that  number  of  contacts  per 
second  with  the  wire  attached  to  the  lever,  G. 

At  each  contact  a  circuit  is  completed  through  the  coils  of  the  receiver,  and 
produces  a  sound  resembling  that  made  by  the  “death-watch,”  which,  by 
rapid  repetition,  forms  the  musical  note  sung  into  the  transmitter. 


THE  TELEPHONE. 


467 


Before  going  to  press  we  note  another  most  excellent  article  on  the  Tele¬ 
phone  in  “  Nature,”  which  further  elucidates  this  interesting  subject : 

Paper  read  by  Mr.  W.  H.  Preece,  M.I.C.E.,  at  the  Plymouth 
Meeting  of  the  British  Association. 

In  the  following  paper  I  call  instruments  employed  in  the  transmission  of 
musical  sounds,  Tone  Telephones,  and  those  employed  in  the  transmission  of 
the  human  voice.  Articulating  Telephones. 

In  the  year  1837,  Page,  an  American  physicist,  discovered  that  the  rapid 
magnetization  and  demagnetization  of  iron  bars  produced  what  he  called 
“galvanic  music.”  Musical  notes  depend  upon  the  number  of  vibrations 
imparted  to  the  air  per  second.  If  these  exceed  sixteen  we  obtain  distinct 
notes.  Hence,  if  the  currents  passing  through  an  electro-magnet  be  made 
and  broken  more  than  sixteen  times  per  second,  we  obtain  “  galvanic  music  ” 
by  the  vibrations  which  the  iron  bar  imparts  to  the  air.  The  iron  bar  itself 
imparts  these  vibrations  by  its  change  of  form  each  time  it  is  magnetized  or 
demagnetized. 

De  la  Rive,  of  Geneva,  in  1843,  increased  these  musical  effects  by  operating 
on  long  stretched  wires  which  passed  through  open  bobbins  of  insulated  wire 


J-ine. 


FIG.  X. 


Philip  Reiss,  of  Friedrichsdorf,  in  1861,  produced  the  first  telephone  which 
reproduced  musical  sounds  at  a  distance.  He  utilized  the  discovery  of  Page 
by  causing  a  vibrating  diaphragm  to  rapidly  make  and  break  a  galvanic 
circuit.  The  principle  of  his  apparatus  is  shown  Fig.  X. 

b  is  a  hollow  wooden  box  into  which  the  operator  sings  through  the  mouth¬ 
piece  a.  The  sound  of  his  voice  throws  the  diaphragm  c  into  rapid  vibration 
so  as  to  make  and  break  contact  at  the  platinum  points  d  at  each  vibration. 
This  interrupts  the  current  flowing  from  the  batteries  e  as  often  as  the  dia¬ 
phragm  vibrates,  and  therefore  magnetizes  and  demagnetizes  the  electro¬ 
magnet  as  often.  Hence  whatever  note  be  sounded  into  the  box  a ,  the 
diaphragm  c  will  vibrate  to  that  note,  and  the  electro-magnet  f  will  similarly 
respond  and  therefore  repeat  that  note. 

Musical  sounds  vary  in  tone,  in  intensity,  and  in  quality.  The  tone  depends 
on  the  number  of  vibrations  per  second  onlY  ;  the  intensity  on  the  amplitude 
or  extent  of  those  vibrations  ;  the  quality  on  the  form  of  the  waves  made  by 
the  vibrating  particles  of  air. 

It  is  evident  that  in  Reiss’s  telephone  everything  at  the  receiving  end 
remains  the  same,  excepting  the  number  of  vibrations,  and  therefore  the 
sounds  emitted  by  it  varied  only  in  tone,  and  were  therefore  notes  and  nothing 

30-  2 


468 


MAGNETISM. 


more.  The  instrument  remained  a  pretty  philosophical  toy,  and  was  of  no 
practical  value. 

Cromwell  Varley,  in  1870,  showed  how  sounds  could  be  produced  by  rapidly 
charging  and  discharging  a  condenser. 

After  alluding  to  the  invention  of  Mr.  Elisha  Gray  (“  Nature,”  vol.  xiv.  p. 
30),  Mr.  Preece  said  : 

It  remained  for  Prof.  Graham  Bell,  of  Boston,  who  has  been  working  at 
this  question  with  the  true  spirit  of  a  philosopher  since  1872,  to  make  the 
discovery  by  which  tone,  intensity,  and  quality  of  sounds  can  all  be  sent.  He 
has  rendered  it  possible  to  reproduce  the  human  voice  with  all  its  modulations 
at  distant  points.  I  have  spoken  with  a  person  at  various  distances  up  to 
thirty-two  miles  ;  and  through  about  a  quarter  of  a  mile  I  have  heard  Prof. 
Bell  breathe,  laugh,  sneeze,  cough,  and,  in  fact,  make  any  sound  the  human 
voice  can  produce.  Without  explaining  the  various  stages  through  which  his 
apparatus  has  passed,  it  will  be  sufficient  to  explain  it  in  its  present  form. 
Like  Reiss,  he  throws  a  diaphragm  into  vibration,  but  Prof.  Bell’s  diaphragm 


JLvne 


is  a  disc  of  thin  iron,  a ,  which  vibrates  in  front -of  a  soft  iron  core,  b,  attached 
to  the  pole  of  a  permanent  bar  magnet,  N  S  (Fig.  y).  This  core  becomes 
magnetized  by  the  influence  of  the  bar  magnet,  N  S,  inducing  all  around  it  a 
magnetic  field,  and  attracting  the  iron  diaphragm  towards  it.  Around  this 
core  is  wound  a  small  coil,  c,  of  No.  38  silk-covered  copper  wire.  One  end  of 
this  wire  is  attached  to  the  line  wire,  the  other  is  connected  to  the  earth.  The 
apparatus  at  each  end  is  identically  similar,  so  that  it  becomes  alternately 
transmitter  and  receiver,  first  being  put  to  the  mouth  to  receive  sounds,  and 
then  to  the  ear  to  impart  them.  Now,  the  operation  of  this  apparatus  depends 
upon  the  simple  fact  that  any  motion  of  the  diaphragm,  a,  alters  the  condition 
of  the  magnet  field  surrounding  the  core,  b,  and  any  alteration  of  the  magnet 
field,  that  is,  either  its  strengthening  or  weakening,  means  the  induction  of  a 
current  of  electricity  in  the  Coil,  c.  Moreover,  the  strength  of  this  induced 
current  depends  upon  the  amplitude  of  the  vibration,  and  on  the  form  and 
rate  of  the  vibration.  The  number  of  currents  sent,  of  course,  depends  upon 
the  number  of  vibrations  of  the  diaphragm.  Now,  each  current  induced  in 
the  coil,  c,  passes  through  the  line  wire  to  the  coil,  c1,  and  then  it  alters  the 
magnetization  of  the  core,  bl,  increasing  or  diminishing  its  attraction  for  the 
iron  diaphragm,  a1.  Hence  the  diaphragm,  a1,  is  vibrated  also,  and  every 
vibration  of  the  diaphragm  a  must  be  repeated  on  the  diaphragm  a 1  with  a 
strength  and  form  that  must  vary  exactly  together.  Hence,  whatever  sound 
produces  the  vibration  of  a  is  repeated  by  a \  because  its  vibrations  are  an 
exact  repetition  of  those  of  a. 


THE  TELEPHONE. 


469 


It  is  quite  evident,  however,  that  Bell’s  telephone  is  limited  in  its  range. 
The  currents  operating  it  are  very  weak,  and  it  is  so  sensitive  to  currents  that 
when  attached  to  a  wire  which  passes  in  the  neighbourhood  of  other  wires,  it 
is  subject  to  be  acted  upon  by  every  current  that  passes  through  any  one  of 
those  wires.  Hence  on  a  busy  line  it  emits  sounds  that  are  very  like  the 
pattering  of  hail  against  a  window,  and  which  are  so  loud  as  to  overpower  the 
effects  of  the  human  voice. 

Now,  Mr.  T.  A.  Edison,  of  New  York,  has  endeavoured  to  remedy  these 
defects  in  Bell’s  by  introducing  a  transmitter  which  is  operated  by  battery 
currents  whose  strength  is  made  to  vary  directly  with  the  quality  and  intensity 
of  the  human  voice.  In  carrying  out  his  investigations  in  this  held  he  has 
discovered  the  curious  fact  that  the  resistance  of  plumbago  varies  in  some 
ratio  inversely  with  the  pressure  brought  to  bear  upon  it.  Starting  from 
Reiss’s  transmitter,  he  simply  substitutes  for  the  platinum  point  id)  a  small 
cylinder  of  plumbago,  and  he  finds  that  the  resistance  of  this  cylinder  varies 
sufficiently  with  the  pressure  of  the  vibration  of  the  diaphragm  to  cause  the 
currents  transmitted  by  it  to  vary  in  form  and  strength  to  reproduce  all  the 
varieties  of  the  human  voice.  His  receiver  also  is  novel  and  peculiar.  In 
1874  he  discovered  that  the  friciion  between  a  platinum  point  and  moist 


chemically-prepared  paper  varied  every  time  a  current  was  passed  between 
the  two,  so  that  the  rate  with  which  the  paper  moved  was  altered  at  will. 
Now,  by  attaching  Fig.  Z  to  a  resonator,  a ,  a  spring,  b ,  whose  platinum  face,  c , 
rested  on  the  chemically-prepared  paper,  d,  whenever  the  drum,  <?,  was  rotated 
and  currents  sent  through  the  paper,  the  friction  between  c  and  d  is  so  modified 
that  vibrations  are  produced  in  the  resonator,  a ,  and  these  vibrations  are  an 
exact  reproduction  of  those  given  out  by  the  transmitter  at  the  other  station. 

Edison’s  telephone,  though  not  in  practical  use  in  America,  is  under  trial. 
In  some  experiments  made  with  it  songs  and  words  were  distinctly  heard 
through  12,000  ohms,  equal  to  a  distance  of  1,000  miles  of  wire. 

Bell’s  telephone  is,  however,  in  practical  use  in  Boston,  Providence,  and 
New  York.  There  are  several  private  lines  that  use  it  in  Boston,  and  several 
more  under  construction.  1  tried  two  of  them,  and  though  we  succeeded  in 
conversing,  the  result  was  not  so  satisfactory  as  experiment  led  one  to 
anticipate.  The  interferences  of  working  wires  will  seriously  retard  the 
employment  of  this  apparatus,  but  there  is  no  doubt  that  scientific  inquiry 
and  patient  skill  will  rapidly  eliminate  all  practical  defects. 

To  Prof.  Graham  Bell  must  be  accorded  the  full  credit  of  being  the  first  to 
transmit  the  human  voice  to  distances  beyond  the  reach  of  the  ear  and  the 
eye  by  means  of  electric  currents. 


470 


MAGNETISM. 


The  completion  of  the  articles  on  Light,  Heat,  Electricity,  and  Mag¬ 
netism,  &c.,  cannot  be  better  consummated  than  by  a  report,  which  appeared 
in  the  “  Literary  Gazette,”  of  Faraday’s  lecture  at  the  Royal  Institution, 

On  the  Conservation  of  Force. 

“  When  we  occupy  ourselves  with  the  dual  forms  of  power,  electricity  and 
magnetism,  we  find  great  latitude  of  assumption:  and  necessarily  so,  for  the 
powers  become  more  and  more  complicated  in  their  conditions.  But  still  there 
is  no  apparent  desire  to  let  loose  the  force  of  the  principle  of  conservation, 
even  in  those  cases  where  the  appearance  and  disappearance  of  force  may 
seem  most  evident  and  striking.  Electricity  appears  when  there  is  consump¬ 
tion  of  no  other  force  than  that  recjuired  for  friction;  we  do  not  know  how, 
but  we  search  to  know,  not  being  willing  to  admit  that  the  electric  force  can 
arise  out  of  nothing.  The  two  electricities  are  developed  in  equal  proportions; 
and,  having  appeared,  we  may  dispose  variously  of  the  influence  of  one  upon 
successive  portions  of  the  other,  causing  many  changes  in  relation,  yet  never 
able  to  make  the  sum  of  the  force  of  one  kind  in  the  least  degree  exceed,  or 
come  short  of,  the  sum  of  the  other.  In  that  necessity  of  equality  we  see  an¬ 
other  direct  proof  of  the  conservation  of  force  in  the  midst  of  a  thousand 
changes  that  require  to  be  developed  in  their  principles  before  we  can  consider 
this  part  of  science  as  even  moderately  knoVvn  to  us.  One  assumption  with 
regard  to  electricity  is,  that  there  is  an  electric  fluid  rendered  evident  by  excite¬ 
ment  in  plus  and  minus  proportions.  Another  assumption  is,  that  there  are 
two  fluids  of  electricity,  each  particle  of  each  repelling  all  particles  like  itself, 
and  attracting  all  particles  of  the  other  kind  always,  and  with  a  force  propor¬ 
tionate  to  the  inverse  square  of  the  distance,  being  so  far  analogous  to  the 
definition  of  gravity.  This  hypothesis  is  antagonistic  to  the  law  of  the  con¬ 
servation  of  force,  and  open  to  all  the  objections  that  have  been,  or  may  be, 
made  against  the  ordinary  definition  of  gravity.  Another  assumption  is,  that 
each  particle  of  the  two  electricities  has  a  given  amount  of  power,  and  can 
only  attract  contrary  particles  with  the  sum  of  that  amount,  acting  upon  each 
of  two  with  only  half  the  power  it  could,  in  like  circumstances,  exert  upon  one. 
But  various  as  are  the  assumptions,  the  conservation  of  force,  though  wanting 
in  the  second,  is,  I  think,  intended  to  be  included  in  all.  I  might  repeat  the 
same  observations  nearly  in  regard  to  magnetism, — whether  it  be  assumed  as 
a  fluid  or  two  fluids  or  electric  currents  —  whether  the  external  action  be  sup¬ 
posed  to  be  action  at  a  distance  or  dependent  on  an  external  condition  and 
lines  of  force — still  all  are  intended  to  admit  the  conservation  of  power  as  a 
principle  to  which  the  phenomena  are  subject.  The  principles  of  physical 
knowledge  are  now  so  far  developed  as  to  enable  us  not  merely  to  define  or 
describe  the  known,  but  to  state  reasonable  expectations  regarding  the  un¬ 
known;  and  I  think  the  principle  of  the  conservation  of  force  may  greatly 
aid  experimental  philosophers  in  that  duty  to  science  which  consists  in  the 
enunciation  of  problems  to  be  solved.  It  will  lead  us,  in  any  case  where  the 
force  remaining  unchanged  in  form  is  altered  in  direction  only,  to  look  for  the 
new  disposition  of  the  force,  as  in  the  cases  of  magnetism,  static  electricity, 
and  perhaps  gravity,  and  tc  ascertain  that  as  a  whole  it  remains  unchanged 
in  amount;  or,  if  the  original  force  disappear,  either  altogether  or  in  part, 
it  will  lead  us  to  look  for  the  new  condition  or  form  of  force  which  should 
result,  and  to  develop  its  equivalency  to  the  force  that  has  disappeared.  Like¬ 
wise,  when  force  is  developed,  it  will  cause  us  to  consider  the  previously 


CONSERVATION  OF  FORCE. 


47* 


existing  equivalent  to  the  force  so  appearing;  and  many  such  cases  there  are 
in  chemical  action.  When  force  disappears,  as  in  the  electric  or  magnetic 
induction  after  more  or  less  discharge,  or  that  of  gravity  with  an  increasing 
distance,  it  will  suggest  a  research  as  to  whether  the  equivalent  change  is  one 
within  the  apparently  acting  bodies  or  one  external  (in  part)  to  them.  It  will 
also  raise  up  inquiry  as  to  the  nature  of  the  internal  or  external  state,  both 
before  the  change  and  after.  If  supposed  to  be  external,  it  will  suggest  the 
necessity  of  a  physical  process,  by  which  the  power  is  communicated  from 
body  to  body ;  and  in  the  case  of  external  action,  will  lead  to  the  inquiry 
whether,  in  any  case,  there  can  be  truly  action  at  a  distance,  or  whether  the 
ether,  or  some  other  medium,  is  not  necessarily  present.  We  are  not  permitted 
as  yet  to  see  the  nature  of  the  source  of  physical  power,  but  we  are  allowed 
to  sec  much  of  the  consistency  existing  amongst  the  various  forms  in  which  it 
is  presented  to  us.  Thus  if,  in  static  electricity,  we  consider  an  act  of  induc¬ 
tion,  we  can  perceive  the  consistency  of  all  other  like  acts  of  induction  with 
it.  If  we  then  take  an  electric  current,  and  compare  it  with  this  inductive 
effect,  we  see  their  relation  and  consistency.  In  the  same  manner  we  have 
arrived  at  a  knowledge  of  the  consistency  of  magnetism  with  electricity,  and 
also  of  chemical  action  and  of  heat  with  all  the  former ;  and  if  we  see  not  the 
consistency  between  gravitation  with  any  of  these  forms  of  force,  I  am  st.ongiy 
of  the  mind  that  it  is  because  of  our  ignorance  only.  How  imperfect  would 
our  idea  of  an  electric  current  now  be  if  we  were  to  leave  out  of  sight  its 
origin,  its  static  and  dynamic  induction,  its  magnetic  influence,  its  chemical 
and  heating  effects?  or  our  idea  of  any  one  of  these  results,  if  we  left  any  of 
the  others  unregarded?  That  there  should  be  a  power  of  gravitation  existing 
by  itself,  having  no  relation  to  the  other  natural  powers ,  and  no  respect  to  the 
law  of  the  conservation  of  force ,  is  as  little  likely  as  that  there  should  be  a 
principle  of  levity  as  well  as  of  gravity.  Gravity  may  be  only  the  residual 
part  of  the  other  forces  of  nature,  as  Mossotti  has  tried  to  show;  but  that  it 
should  fall  out  from  the  law  of  all  other  force,  and  should  be  outside  the  reach 
either  of  further  experiment  or  philosophical  conclusions,  is  not  probable.  So 
we  must  strive  to  learn  more  of  this  outstanding  power,  and  endeavour  to 
avoid  any  definition  of  it  which  is  incompatible  with  the  principles  of  force 
generally,  for  all  the  phenomena  of  nature  lead  us  to  believe  that  the  great 
and  governing  law  is  one.  I  would  much  rather  incline  to  believe  that  bodies 
affecting  each  other  by  gravitation  act  by  lines  of  force  of  definite  amount 
(somewhat  in  the  manner  of  magnetic  or  electric  induction,  though  without 
polarity),  or  by  an  ether  pervading  all  parts  of  space,  than  admit  that  the 
conservation  of  force  can  be  dispensed  with.  It  may  be  supposed  that  one 
who  has  little  or  no  mathematical  knowledge  should  hardly  assume  a  right  to 
judge  of  the  generality  and  force  of  a  principle  such  as  that  which  forms  the 
subject  of  these  remarks.  My  apology  is  this:  I  do  not  perceive  that  a  mathe¬ 
matical  mind,  simply  as  such,  has  any  advantage  over  an  equally  acute  mind 
not  mathematical  in  perceiving  the  nature  and  power  of  a  natural  principle  of 
action.  It  cannot  of  itself  introduce  the  knowledge  of  any  new  principle. 
Dealing  with  any  and  every  amount  of  static  electricity,  the  mathematical 
mind  can  and  has  balanced  and  adjusted  them  with  wonderfid  advantage, 
and  has  foretold  results  which  the  experimentalist  can  do  no  more  than  verify. 
But  it  could  not  discover  dynamic  electricity,  nor  electro-magnetism,  nor 
magneto-electricity,  nor  even  suggest  them  ;  though,  when  once  discovered  by 
the  experimentalist,  it  can  take  them  up  with  extreme  facility.  So  in  respect 


472 


MAGNETISM. 


of  the  force  of  gravitation,  it  has  calculated  the  results  of  the  power  in  suck 
a  wonderful  manner  as  to  trace  the  known  planets  through  their  courses  and 
perturbations,  and  in  so  doing  has  discovered  a  planet  before  unknown ;  but 
there  may  be  results  of  the  gravitating  force  of  other  kinds  than  attraction 
inversely  as  the  square  of  the  distance,  of  which  it  knows  nothing,  can  discover 
nothing,  and  can  neither  assert  nor  deny  their  possibility  or  occurrence.  Under 
_hese  circumstances,  a  principle,  which  may  be  accepted  as  equally  strict  with 
mathematical  knowledge,  comprehensible  without  it,  applicable  by  all  in  their 
philosophical  logic,  whatever  form  that  may  take,  and,  above  all,  suggestive, 
encouraging,  and  instructive  to  the  mind  of  the  experimentalist,  should  be  the 
more  earnestly  employed  and  the  more  frequently  resorted  to  when  we  are 
labouring  either  to  discover  new  regions  of  science,  or  to  map  out  and  develop 
those  which  are  known  into  one  harmonious  whole;  and  if  in  such  strivings 
we,  whilst  applying  the  principle  of  conservation,  see  but  imperfectly,  still  we 
should  endeavour  to  see,  for  even  an  obscure  and  distorted  vision  is  better  than 
none.  Let  us,  if  we  can,  discover  a  new  thing  in  any  shape;  the  true  appear¬ 
ance  and  character  will  be  easily  developed  afterwards.  Some  are  much 
surprised  that  I  should,  as  they  think,  venture  to  oppose  the  conclusions  of 
Newton  :  but  here  there  is  a  mistake.  I  do  not  oppose  Newton  on  any  point; 
it  is  rather  those  who  sustain  the  idea  of  action  at  a  distance  that  contradict 
him.  Doubtful  as  I  ought  to  be  of  myself,  1  am  certainly  very  glad  to  feel  that 
my  convictions  are  in  accordance  with  his  conclusions.  At  the  same  time,  those 
who  occupy  themselves  with  such  matters  ought  not  to  depend  altogether  upon 
authority,  but  should  find  reason  within  themselves,  after  careful  thought  and 
consideration,  to  use,  and  abide  by,  their  own  judgment.  Newton  himself, 
whilst  referring  to  those  who  were  judging  his  views,  speaks  of  such  as  are 
competent  to  form  an  opinion  in  such  matters,  and  makes  a  strorg  distinction 
between  them  and  those  who  were  incompetent  for  the  case.  But,  after  all, 
the  principle  of  the  conservation  of  force  may  by  some  be  denied.  Well,  then, 
if  it  be  unfounded  even  in  its  application  to  the  smallest  pari,  of  the  science  of 
force,  the  proof  must  be  within  our  reach,  for  all  physical  science  is  so.  In 
that  case,  discoveries  as  large  or  larger  than  any  yet  made  may  be  anticipated. 
'  do  not  resist  the  search  for  them,  for  no  one  can  do  harm,  but  only  good, 
who  works  with  an  earnest  and  truthful  spirit  in  such  a  direction.  But  let  us 
not  admit  the  destruction  or  creation  of  force  without  clear  and  constant  proof. 
Just  as  the  chemist  owes  aii  the  perfection  of  his  science  to  his  dependence 
on  the  certainty  of  gravitation  applied  by  the  balance,  so  may  the  physical 
philosopher  expect  to  find  the  greatest  security  and  the  utmost  aid  in  the  prin¬ 
ciple  of  the  conservation  of  force.  All  that  we  have  that  is  good  and  safe,  as 
the  steam-engine,  the  electric  telegraph,  &c.,  witness  to  that  principle, — it 
would  require  a  perpetual  motion,  a  fire  without  heat,  heat  without  a  source, 
action  without  reaction,  cause  without  effect,  or  effect  without  a  cause,  to  dis¬ 
place  it  from  its  rank  as  a  law  of  nature.” 


PNEUMATICS. 

U  N  DER  the  streets !  What  a  curious  but  indispensable  series  of  utilities  is 
to  be  found  beneath  the  stony  ways  of  this  vast  city  !  To-day  our  cabs  can¬ 
not  make  way  because  the  streets  are  up  for  the  new  water-pipes ;  to-morrow  it 
is  gas;  many  months  ago  it  was  sewage;  and  further  back  it  was  the  tubes 
of  the  Pneumatic  Despatch  Company.  Air  made  the  slave  of  man  !  Air,  which 
generally  wafts  the  aeronaut  on  such  a  wild  and  doubtful  path,  is  here  en¬ 
chained,  and  made  to  behave  itself.  The  air  cannot  blow  the  parcels  hither 
and  thither,  like  the  gossamer  of  the  school-boys — the  supposed  herald,  in 
youthful  days,  of  a  cake;  but  work  it  must,  in  one  direction  or  the  other,  by 
the  iron  will  of  man,  through  another  power,  the  steam-engine,  moving  a 
very  important  instrument  called  the  “  Blower.  ’ 

Hippocrates  expressed  the  deep-drawn  inspiration  by  ITi'eiyxa;  and  it  may 
be  supposed  that,  in  consideration  of  the  labour  required  to  work  an  air- 
pump,  particularly  one  of  the  old  days,  they  agreed  to  call  the  experiment 
“  pneumatic,”  and  to  class  the  whole  series  of  facts  under  one  common  title 
of  Pneumatics.  Be  this  as  it  may,  they  styled  the  latter  the  sister  of  Hydro¬ 
statics,  and  considered  both  to  be  a  branch  of  Mechanics. 

The  learned  Boerhaave  considered  air  (the  matter  surrounding  our  terra¬ 
queous  globe)  as  “  a  universal  chaos  or  colluvies  of  all  kinds  of  created  bodies, 
besides  the  matter  of  light  or  fire  which  continually  flows  into  it  horn  the 


474 


PNEUMATICS. 


heavenly  bodies,  and  probably  the  magnetic  effluvia  of  the  earth  :  whatever 
fire  can  volatilize  is  found  in  the  air.” 

Aristotle,  reviewing  the  four  ancient  elements,  says  they  all  have  weight, 
fire  excepted ;  and  he  adds,  that  a  bladder  lull  of  air  weighs  more  than  when 
it  is  quite  emoty. 

It  is  the  closed  bladder  that  proves,  on  pressure,  that  air  fills  space,  to  the 
exclusion  of  other  matter,  until  it  is  removed;  that,  in  fact,  air  has  the  pro¬ 
perty  conveniently  expressed  by  the  term  “  impenetrability.”  The  bellows 
corked,  a  bladder  full  of  air,  and  well  secured  at  the  orifice  with  waxed 
string,  an  umbrella  turned  inside  out  by  the  force  of  air,  the  wind,  demon¬ 
strate,  in  a  simple  but  conclusive  manner,  the  materiality  of  that  which  phi¬ 
losophers  prefer  to  estimate  as  a  mechanical  agent  with  the  assistance  of  the 
air-pump. 

Sprengel’s  air-pump  is  the  prettiest  and  most  simple  arrangement  for  certain 


experiments  which  it  is  not  necessary 
to  conduct  on  the  large  scale.  This 
pump  (if  it  may  be  so  called)  will  be  ex¬ 
plained  presently.  As  a  contrast  to  it, 
we  have  the  powerful  and  useful  pump 
of  Mr.  C.  W.  Siemins,  now  made  by  the 
good  successor  to  Knight,  of  Foster 
Lane,  City,  viz.,  Mr.  James  Howe.  The 
inventor's  pump  is  thus  described: 

“  The  Siemins  air-pump  consists  of 
two  cylinders,  differing  in  magnitude,  of 
which  the  smaller  is  applied  either  to  the 
bottom  or  top  of  the  larger,  while  the 
valved  pistons  belonging  to  each  respec¬ 
tively  are  attached  to  the  same  piston- 
rod.  The  air  withdrawn  from  the  re¬ 
ceiver,  or  other  vessel  intended  to  be 
exhausted,  is  condensed  in  the  lower  cy¬ 
linder  into  one-fourth  part  of  its  original 
volume,  and  consequently  always  pos¬ 
sesses  sufficient  elasticity  to  pass  through 
the  discharging  valve  and  escape  into 
the  atmosphere,  the  opposing  pressure  of 
which  on  that  valve  is  thus  counteracted 
in  a  manner  perfectly  novel. 

“  The  following  are  the  parts  of  which 
this  instrument  consist:,  as  shown  in  the 
annexed  sectional  view  (Fig.  402): 

“  The  exhausting  cylinder,  A.  A  second 
cylinder,  B,  equal  in  length  to  the  first,  to 
the  bottom  of  which  (in  the  form  of  the 
instrument  here  represented)  it  is  fixed, 
but  having  only  one-third  or  one-fourth 
of  its  sectional  area,  and  only  one-third 
or  one-fourth,  therefore,  of  its  cubical 
contents. 

“  The  cylinders  are  separated  by  n 


THE  AIR-PUMP. 


Fig.  403. 


plate  forming  at  once  the  bottom  of  the  upper  and  the  top  of  the  lower 
cylinder,  the  only  air-passage  between  them  being  a  silk  valve,  v . 


PNEUMATICS. 


476 


“  In  each  cylinder  works  a  valved  piston,  P,  and/,  attached  to  a  piston-rod 
common  to  both,  which  passes  through  a  stuffing-box  in  the  plate.  The  dis¬ 
tance  between  the  p  stons  is  such  that,  when  P  is  in  contact  with  the  top  of 
the  upper  or  exhausting  cylinder,  p  is  in  contact  with  the  top  of  the  small  or 
lower  cylinder  ;  and  when  P  is  in  contact  with  the  bottom  of  the  large  cylinder, 
p  is  in  contact  with  that  of  the  small  cylinder.  The  pump-plate,  E,  placed 
above  the  large  cylinder  A,  supports  the  receiver  R,  or  other  vessel  to  be  ex¬ 
hausted,  from  which  the  air  flows  through  the  valve  v ,  during  the  descent  of 
the  piston  P. 

“  Fig.  403  represents  the  complete  pump,  as  manufactured  for  philosophical 
purposes.  The  motion  of  the  pistons  is  effected  by  means  of  a  short  crank 
with  a  jointed  connecting-rod,  converting  the  circular  motion  given  by  the 
lever  handle  into  a  vertical  one,  which  is  maintained  by  means  of  a  cross-head, 
with  rollers  working  between  guides. 

“  The  action  of  this  air-pump  is  as  follows : 

“On  the  descent  of  the  piston  P,  tending  to  produce  a  vacuum  in  the  ex¬ 
hausting  cylinder,  A,  by  causing  a  difference  of  pressure  above  and  below  the 
first  valve,  v,  in  the  top  of  the  cylinder,  the  elasticity  of  the  air  in  the  receiver  j 
causes  it  to  pass  through  the  valve  v.  The  air  below  the  piston,  P,  is  at  the 
same  time  pressed  through  the  valve,  v ,  in  the  plate  separating  the  cylinders, 
and  enters  the  cylinder,  B,  in  which  a  vacancy  is  simultaneously  made  for  it 
by  the  descent  of  the  piston  p;  and,  in  consequence  of  the  difference  of 
capacity  of  the  two  cylinders,  it  becomes  reduced  to  one-fourth  of  its  original  j 
bulk,  its  elasticity,  according  to  the  well-known  law,  being  proportionally  in¬ 
creased.  The  air  contained  in  the  small  cylinder  below  the  piston,/,  will,  in  i 
like  manner,  be  pressed  through  the  valves,  v,  7/",  into  the  atmosphere. 

“  During  the  ascent  of  the  p. stons,  the  valves,  v,  v',  v",  will  be  closed,  and 
the  valves,  w,  w,  in  the  pistons  opened  by  the  upward  pressure  of  the.  air  in 
the  cylinders  and  atmosphere,  admitting  the  air  in  each  cylinder  to  pass  through  , 
the  pistons  as  they  rise,  in  order  that,  in  the  following  downward  movement, 
the  air,  which  during  the  previous  stroke  of  the  pump  issued  from  the  receiver 
into  the  exhausting  cylinder,  may  be  withdrawn  from  that  into  the  lower  I 
cylinder,  while  the  air  condensed  in  the  latter  may  be  finally  expelled  into  the 
atmosphere.  By  this  construction  of  the  instrument  we  are  enabled  to  obtain  | 
a  more  perfect  vacuum  than  by  any  air-pump  previously  devised. 

“  In  order  to  prove  this,  let  us  compare  the  action  of  two  air-pumps,  one  of 
the  improved,  the  other  of  the  usual  construction,  assuming  that  they  are  ; 
equally  perfect  in  workmanship.  If  an  air-pump  could  discharge  the  entire  ! 
quantity  of  air  contained  in  it  at  the  end  of  every  stroke  of  the  piston,  and  if 
the  action  of  the  valves  were  also  perfect,  there  would  be  nothing  to  prevent 
our  obtaining  a  perfect  vacuum.*  But  whoever  has  tried  the  experiment  will  [ 
have  found  that  an  ordinary  philosophical  air-pump  does  not  remove  much 


*  The  inventor  of  the  new  air-pump  makes  the  following  remarks  on  this  subject: — “It  is  the 
opinion  of  some  natural  philoiophers  that  the  whole  of  the  air  could  never  be  exhausted  from  a  closed 
vessel  by  means  of  a  pump,  even  if  the  apparatus  were  iheoreticallv  perfect.  From  that  opinion,  how¬ 
ever,  I  must  beg  leave  to  dissent ;  for,  even  if  the  repulsive  force  which  separates  the  atoms  of  fluids  ! 
were  itself  unlimited  (which,  however,  has  never  been  proved),  there  necessarily  must  be  a  limit  where  * 
that  force  and  the  force  of  gravity  acting  on  a  single  particle  just  equal  each  other  .  and  if  a  vessel  weie  ; 
emptied  of  air  to  this  extent,  and  a  further  portion  were  withdrawn,  the  remainder  would  no  longer  be 
able  to  fill  the  whole  vessel,  but  would  cover  the  bottom  only,  as  anon-elastic  fluid  would,  leaving  a  | 
perfect  vacuum  above.  In  this  state  of  things,  continual  withdrawals  of  air  from  the  lower  part  of  the 
vessel  would  at  length  cause  the  last  atom  itself  to  be  wi.hdrawn.” 


THE  AIR-PUMP. 


477 


more  than  of  the  atmosphere  from  the  receiver,  however  long  he  may 
have  continued  to  work  the  instrument.  We  may  conclude,  therefore,  even 
when  the  piston  is  in  contact  with  the  bottom  of  the  cylinder,  that  there  still 
remains  a  space  equal  to  of  the  capacity  of  the  cylinder,  through  which 
the  piston  cannot  be  depressed,  and  where  the  air  is  merely  condensed,  ex¬ 
panding  and  refilling  the  whole  cylinder  when  the  piston  is  raised. 

“  Now,  let  us  suppose  that  in  the  new  air-pump  the  piston,  P,  leaves  _ i_  of 
the  air  in  the  exhausting  cylinder,  A,  undisplaced,  and  that  the  piston,/,  can¬ 
not  be  brought  within  part  of  the  length  of  stroke  of  the  top  or  bottom 
of  the  smaller  cylinder,  the  working  having  been  continued  until  no  further 
exhaustion  is  effected.  At  this  period,  the  piston,  /,  will  leave  in  the  cylinder, 
B,  during  the  downward  stroke,  Ti-0-  of  its  bulk  of  air  of  the  atmospheric 
density  unexhausted:  if  it  be  raised  again,  this  portion  of  air  will  expand  and 
fill  the  cylinder,  B,  with  air,  the  density  of  which  will  be  only  that  of  the 
atmosphere.  The  piston,  P,  will  at  the  same  time  ascend  to  the  top  of  the 
exhausting  cylinder,  A,  filled  with  air  of  the  same  density  as  that  remaining  in 
the  receiver;  but,  the  exhaustion  having  reached  its  utmost  limit,  during  the 
next  downward  stroke  no  air  will  be  discharged  from  cylinder  A  into  cylinder 
B  :  the  air  above  the  piston  in  the  latter  will,  at  the  termination  of  this  stroke, 
have  expanded  ioo  times,  and,  having  previously  expanded  to  an  equal  amount 
during  the  upward  stroke,  it  will  now  be  reduced  to  the  density  that  of 

the  atmosphere.  If  no  force  were  required  to  open  the  valve,  P,  air  would,  in 
this  state  of  things,  pass  from  the  upper  into  the  lower  cylinder,  unless  that  in 
the  former,  ioo  times  compressed  as  it  would  be  at  the  end  of  the  downward 
stroke,  were  not  still  rarefied  10,000  times,  or — what  is  the  same  thing — if  it 
were  not,  when  it  filled  the  cylinder  A,  1,000,000  times  rarefied.  We  find, 
therefore,  that  by  the  addition  of  the  second  cylinder  the  vacuum  may  be  ren¬ 
dered  10,000  times  more  perfect  than  if  the  cylinder  A  had  been  employed 
alone  in  the  manner  of  an  air-pump.* 

“As  the  leakage  of  the  valves  and  piston  is  a  principal  cause  of  the  imper¬ 
fection  of  the  vacuum  obtained  by  means  of  air-pumps  of  the  ordinary  con¬ 
struction,  it  may  be  objected  that,  as  we  have  in  the  new  one  two  valves  and 
one  piston  more  than  usual,  the  loss  of  effect  from  this  cause  will  be  propor¬ 
tionally  greater.  This,  however,  is  not  the  case.  On  the  contrary,  the  loss 
from  leakage  at  the  valves  and  pistons  is  diminished  in  the  new  air-pump 
nearly  in  the  same  ratio  as  the  opposing  unexhausted  space  in  the  cylinder. 
The  amount  of  leakage  through  a  given  aperture  bears  a  certain  proportion  to 
the  difference  of  pressure  on  each  side  (increasing  as  the  square  root  of  the 
pressure);  and  it  will  be  observed  that  this  difference  of  pressure,  especially 
in  the  large  cylinder,  is  very  small  indeed,  and  occurs  at  intervals  only,  where¬ 
as,  in  the  case  of  an  ordinary  single-acting  pump,  the  entire  atmosphere  con¬ 
stantly  rests  on  the  piston  and  exhausting-valve.  Besides,  in  the  new  air-pump 
the  leakage  of  the  air  through  the  apparatus  is  opposed  by  a  greater  number 
of  obstructions,  one  after  another,  between  the  discharging-valve  and  the  le- 


*  Catera  paribus,  if  a  well-made  pump,  of  any  of  the  ordinary  forms,  will  rarefy  the  air  to  oo,  new 
one  would  cam  the  rarefaction  up  to  9^9>'9  if  the  valve,  *t/,  could  be  rendered  automatic. 

Although  iht  reasoning  abo' e  is  *n  some  degree  theoretical,  it  is  independent  of  'he  consideration 
of  extreme  accurac>  in  the  construction  of  the  new  air-pump,  which  will  produce  a  vacuum  approach- 
tug  to  the  perfection  assigned,  jr  pioportion  to  the  smallness  of  the  force  required  to  open  the  \al\e,  v. 


478 


PNEUMATICS. 


ceiver.  Indeed,  the  efficacy  of  the  pump  would  not  be  impaired  in  any  con¬ 
siderable  degree  if  even  the  valve,  v ,  were  removed  altogether,  and  any  one 
of  the  others  should  be  in  a  very  leaky  state. 

“  Another  circumstance  interfering  with  the  power  of  obtaining  a  good  va¬ 
cuum  by  means  of  a  well-made  air-pump  of  any  of  the  forms  previously  con¬ 
structed,  but  which  is  obviated  in  the  instrument  now  described, is, that  the  valve 
through  which  the  air  has  to  pass  from  the  receiver  into  the  pump  is  forced 
into  its  seat  at  the  end  of  the  reversed  stroke  by  the  whole  pressure  of  the 
atmosphere,  minus  only  that  of  the  air  remaining  in  the  receiver.  By  this  the 
silk  valve  is  soon  injured,  and,  what  is  even  more  important,  the  rarefied  air 
has  not  power  to  force  it  open  again,  and  the  exhaustion  consequently  ceases 
before  the  vacuum  has  attained  that  degree  of  perfection  to  which  it  might 
otherwise  be  carried.  One  of  the  most  obvious  objections  to  an  ordinary  air- 
pump,  whether  single  or  double  acting,  arises  from  the  inequality  of  the  force 
required  to  move  the  piston  through  different  portions  of  the  stroke,  and  from 
the  very  great  force  which  is  ultimately  requisite. 


“In  the  diagram  (Fig.  404),  A  is  the  barrel  of  a  double-acting  air-pump 
which,  by  the  alternate  motion  of  the  piston,  P,  and  the  valves  1,  2,  3,  and  4, 
produces  a  partial  vacuum  in  the  receiver  or  closed  vessel,  R.  Let  us  suppose 
that  five-sixths  of  the  air  originally  contained  in  R  have  been  removed,  and 
that  the  working  of  the  pump  is  still  continued.  The  resistance  which  the 
piston  will  now  have  to  encounter  is  readily  found  from  the  law  of  Mariotte, 
and  will  be  represented  by  the  shaded  part  of  the  diagram,  bounded  by  the 
parabolic  curve.  At  the  commencement  of  the  stroke,  the  pressure  on  both 
sides  of  the  piston  being  equal  to  one-sixth  atmosphere,  the  resistance  is  o;  it 
increases  gradually  in  proportion  to  the  diminution  of  the  space  below  the  pis-  ; 
ton,  until  the  air  has  been  compressed  to  one-sixth  of  its  original  volume,  when 


THE  AIR-PUMP. 


479 


its  density  will  have  become  equal  to  that  of  the  atmosphere,  and  the  dis¬ 
charging-valve,  4,  will  be  opened.  It  is  evident,  in  this  case,  that  the  force 
required  to  move  the  piston  to  the  bottom  of  the  cylinder  must  be  sufficient  to 
overcome  the  maximum  resistance,  which  will  be  about  3^  times  greater  than 
the  average  amount  that  would  be  experienced  if  the  entire  resistance  could 
be  distributed  over  the  whole  stroke. 

“In  this  illustration  we  have  supposed  the  pump  to  be  double  acting,  and 
have,  therefore,  deducted  from  the  actual  pressure  against  the  piston  the 
uniform  ‘aiding  pressure’  of  the  air  which  follows  it  freely  from  the  receiver 
through  the  valve,  1. 

“Air-pumps  for  philosophical  purposes  are  very  commonly  single  acting, 
the  pressure  of  the  atmosphere  being  constantly  exerted  on  one  side  of  the 
piston  only ;  but  when  there  are  two  cylinders,  as  is  frequently  the  case,  hav¬ 
ing  their  piston-rods  connected  with  the  opposite  ends  of  the  same  lever,  the 
atmospheric  pressure  on  one  piston  balances  that  on  the  other,  and  the  resist¬ 
ance  will  be  equivalent  to  that  occurring  in  a  pump  with  one  double-acting 
cylinder.  In  a  single-barrel  pump  with  open  top  the  inequality  of  load  is  still 
greater  than  in  a  double-acting  or  double-cylinder  pump.  The  inequality  of 
load  increases  as  the  rarefaction  proceeds,  but  the  resultant  of  the  resistance 
attains  its  maximum  when  the  vacuum  equals  19  in.  cf  mercury  in  the  gauge, 
or  when  nearly  two-thirds  of  the  atmosphere  have  been  removed  from  the  re¬ 
ceiver,  after  which  it  constantly  diminishes. 


Fig.  405. 


“It  will  readily  be  perceived  that  in  the  improved  air-pump  this  great  in¬ 
equality  of  load  does  not  exist,  and  therefore  a  pump  of  several  times  greater 
capacity  than  any  given  one  on  the  ordinary  construction  may  be  worked  with 
equal  facility  and  speed,  because  the  resisting  pressure  against  the  larger  pis¬ 
ton,  p,  cannot  rise  at  the  termination  of  the  stroke  to  more  than  four  times  the 
pressure  of  the  air  still  contained  in  the  receiver,  and  therefore  diminishes  as 
the  perfection  of  the  vacuum  increases;  and  even  of  this  greatest  resisting 
pressure,  one-fourth  part  is  balanced  by  the  pressure,  on  the  top  of  the  piston, 
of  the  air  entering  the  cylinder  from  tfie  receiver,  and  another  fourth  by  the 
increasing  ‘aiding  pressure’  on  the  top  of  the  small  piston,//  and  the  re- 


480 


PNEUMATICS. 


maining  half,  after  a  tolerable  vacuum  has  been  formed,  may  be  almost  en¬ 
tirely  neglected.  The  greatest  resistance  to  the  action  of  the  small  piston  is 
that  of  the  atmosphere,  and  is  equal,  therefore,  to  the  greatest  resistance  in  an 
ordinary  air-pump ;  but  it  must  be  recollected  that  its  area  is  only  one-fourth 
of  the  area  of  the  exhausting  cylinder. 

“  One  modification,  however,  of  the  single-barrel  pump  is  in  a  great  degree 
free  from  the  objections  which  have  been  urged  above  (see  Fig.  40:;).  In  it 
the  atmosphere  is  entirely  excluded,  the  piston  in  its  motion  passing  an  open¬ 
ing  through  which  the  air  issues  from  the  receiver,  and  is  then  discharged  by 
a  valve  into  a  vessel  filled  with  oil.  Pumps  of  this  construction  can  be  ren¬ 
dered  very  perfect,  but  they  are  liable  to  grave  practical  objections,  though  of 
a  different  nature  from  those  applying  to  the  forms  previously  described.  They 
require  more  power  for  working  than  any  other  kind  of  air-pump,  because  the 
air  which  follows  the  piston  in  its  upward  course  has  to  be  impelled  backward 
bodily  into  the  receiver,  until  it  again  passes  the  aperture,  when  it  returns  to 
fill  the  cylinder,  Another  objection  to  its  general  use  arises  from  the  circum¬ 
stance  that  it  requires  to  be  moved  slowly,  and  to  receive  much  attention 
during  the  working. 

“  By  the  double-cylinder  air-pump  now  submitted  to  the  public  a  very  per¬ 
fect  vacuum  may  be  obtained,  even  if  the  stroke  is  short  and  the  pistons  do  not 
touch  the  bottoms  of  the  cylinders;  considerable  practical  advantage  is  also 
realized  by  the  application  of  a  crank  to  give  motion  to  the  pistons.  To  this 
may  be  added  the  consequent  greater  ease  and  speed  of  working,  attended 
with  less  racking  of  the  entire  apparatus,  and  less  injury  to  the  valves,  than 
in  any  form  of  air-pump  previously  constructed. 

“  Finally,  as  to  the  cost,  if  the  perfection  of  the  instrument  be  taken  into 
consideration,  a  great  saving  will  be  obtained. 

“The  manufacturers  have  taken  considerable  pains  to  reduce  the  costas 
far  as  possible:  this  has  been  the  principal  cause  of  delay  in  bringing  this  air- 
pump  before  the  public;  and  they  are  prepared  to  supply  the  patent  air-pump 
of  the  form  represented  in  Fig.  403,  the  lower  or  exhausting  cylinder  of  which 
is  3  in.  in  diameter,  for  ^21.” 

We  now  pass  to  the  description  of  Sprengel’s  apparatus  (Fig.  406). 

The  next  drawing  shows  the  manner  in  which  the  stout  glass  tube,  viz., 
a  barometer  tube,  is  bent.  On  the  centre  of  the  third  bend,  B  (counting  from 
the  funnel  a),  a  perpendicular  short  tube  rises,  with  which  any  vessel— say  a 
tube  required  for  Geissler’s  or  Gassiott’s  experiments — with  exhausted  tubes 
is  attached. 

Into  the  funnel,  A,  mercury  is  poured,  and  as  the  level  of  A  is  higher  than 
that  of  B,  a  time  arrives  when  all  parts  of  the  bent  tube  are  filled  with  the 
mercury,  and  it  begins  to  flow  over  the  last  tube  from  B  to  C,  and  to  fall  into 
the  trough  D,  where,  to  prove  the  dragging  and  adhesive  power  of  mercury  for 
air,  and  to  show  that  every  drop  of  mercury  that  falls  carries  with  it  a  propor¬ 
tionate  quantity  of  air,  the  last  tube,  B  c,  is  curved  at  the  end,  and  passes  under 
a  tube  filled  with  mercury,  and  standing  on  the  shelf  of  the  little  mercurial 
trough  D.  The  result  of  the  fall  of  the  mercury  from  B  to  C  is  most  decided, 
and,  as  the  quicksilver  may  be  continually  baled  out  of  the  trough  and  poured 
into  the  funnel,  the  process  of  exhaustion  is  endless.  The  proof  that  air 
is  dragged  out  of  the  tube  G  under  exhaustion  is  shown  in  the  tube  T,  which 
indicates,  if  graduated,  the  nearly  exact  quantity  of  air  originally  contained 
in  the  Geissler  tube,  G,  now  deprived  of  air. 


THE  AIR-PUMP. 


481 


The  two  air-pumps  are  a  great  contrast  to  each  other :  the  first  (Siemens’s) 
is  intended  for  work  on  the  large  scale  ;  the  second  (Sprengel’s)  will  do  all 
that  a  worker  in  tube-chemistry  could  desire. 

The  Mercury  Machine  or  Improved  Sprengel  Pump  of  Monsieur  Alverg- 
niat  deserves  a  place  here,  on  account  of  the  rapidity  with  which  exhaustion 
may  be  performed  with  its  assistance.  The  vacuum  is  not  so  perfect  as  that 
obtained  by  the  admirable  improvements  of  William  Crookes,  Esq.,  F.R.S., 


Fig.  406. — Sprengel' s  Air-Pump.  FlG.  407. — A  Condensing  Pump. 


referred  to  in  page  8,  Fig.  A  ;  but  it  can  be  produced  in  a  fraction  of  the  time 
required  to  complete  an  experiment  by  his  method. 

The  barometer  is  constructed  with  an  oblong  gas-chamber.  A,  of  which  1 
is  the  tube  ;  c  the  basin,  forming  an  open  vase  at  E,  which  is  movable.  In 
order  to  raise  the  vase  higher  than  A,  it  is  attached  by  an  india-rubber  tu  jo, 
D,  to  the  tube  T.  . 

At  the  commencement  of  an  experiment,  the  vase,  C,  and  the  barometric 
chamber,  A,  is  closed  at  R,  and  full  of  mercury.  If  then  the  basin  01  vase,  c, 
is  lowered,  a  Toricellian  vacuum  is  obtained,  and  the  receiver,  B,  lor  instance, 
being  connected  with  A  by  the  three-way  valve,  R,  arranged  as  in  the  tigm<, 


PNEUMATICS. 


4S2 


THE  AIR-PUMP. 


483 


a ,  the  mercury  falls,  as  shown  in  the  figure,  and  a  portion  of  air  is  drawn  out 
of  B  equal  to  the  first  stroke  of  an  ordinary  pump.  The  operation  is  continued 
by  expelling  the  gas  introduced  into  the  barometric  chamber,  A,  by  means 
of  the  mercury,  which  again  fills  A.  To  do  this  the  valve  R  is  turned  in  the 
position  c  by  the  communication  of  a  quarter  revolution  ;  the  vase  C  is  now 
lifted,  and  the  mercury  enters  the  empty  chamber,  the  gas  which  it  included 
diminishes  in  volume,  and  when  the  equilibrium  is  established,  it  acquires  an 
elastic  force  superior  to  that  of  the  atmosphere,  as  the  mercury  in  the  vase,  C, 
which  communicates  with  the  atmosphere,  has  its  level  more  elevated  than 
the  chamber  A  ;  an  egress  is  given  to  this  gas  by  the  valve  R,  which  is 
opened  as  we  see  it  in  figure  (c)  ;  when  it  is  driven  out,  the  valve  r  is  closed, 
as  shown  in  figure  (p),  the  vase  is  replaced  in  its  former  position,  the  baro¬ 
metric  vacuum  is  formed  again,  and  the  series  of  operations  is  continued  in 
the  order  already  followed. 

Such  is  the  working  of  the  machine  in  its  various  parts.  The  india-rubber 
tube,  D,  forms  only  a  continuation  of  the  vase,  and  the  tubes  of  glass  joined 
by  the  fusion  of  one  into  the  other,  and  whose  valves  are  also  of  glass,  main¬ 
tain  the  vacuum  perfectly. 

Besides  the  portions  already  described  may  be  mentioned  the  reservoir  of 
oil  of  vitriol,  V,  which  dries  the  gas  upon  which  we  wish  to  operate ;  the  barome¬ 
tric  gauge,  M,  which  shows  the  pressure  inside  ;  the  valves,  r,  R,  v,p',p" ,  which 
open  or  shut  the  communications  according  to  the  various  requirements  of 
the  experiment ;  and  the  tube,  T,  to  which  may  be  attached  various  receivers. 

This  machine,  employed  chiefly  for  rarefying  the  gas  which  a  current  of 
electricity  may  pass  through  (as  in  Geissler’s  tubes),  will  produce  quickly  a 
vacuum  equal  to  one-tenth  of  a  millimetre  of  mercury. 

One  English  inch  is  equal  to  25  4  millimetres,  and  the  following  is  a  useful 
comparison  of  French  and  English  measures  of  length  : 

English  Inches.  Feet.  Yards. 

i  Millimetre  =  003937079 
1  Centimetre  =  03937079 
1  Decimetre  =  3'937079 

1  Metre  =  39‘37°79  =  3-80899  =  1093633 

1  Kilometre  =3937°  79  =  328o‘899  =  1093  633 

The  object  of  an  air-pump  is  to  show  the  common  properties  (physical  of 
air,  and,  these  bting  understood,  it  is  also  of  great  use  in  a  variety  of  othei 

philosophical  experiments.  ... 

The  pumps  alreadv  explained  are  exhausting  pumps ;  but  the  same  principles, 
reversed,  afford  an  illustration  of  a  condensing  pump,  such  as  the  one  shown 

at  Fig.  407.  .  ,  j  .  , 

Here  a  very  thick  and  strong  glass  receiver  is  held  tightly  down  with  a 
cross-bar  and  screw  s,  and  by  a  reversed  action  of  the  valves  the  an  is  pumped 
into,  but  not  out  of,  the  vessel. 

The  condensing  air-pump  is  of  great  use  in  supplying  air  to  a  diver. 

A  living  diver  is  soon  provided,  in  the  shape  of  a  mouse  :  this  animal  is 
enclosed  in  a  glass  jar,  open  at  the  bottom,  and  provided  with  a  stage, on  w  lm  1 
the  little  creature  may  stand  without  fear  of  wetting  his  delicate  toes,  am  , 
what  is  of  paramount  importance  (at  least  to  the  animal),  the  jar  is  continua  y 
supplied  with  fresh  air.  The  air  is  pumped  down  to  the  miniature  diving- 
bell  (Fig.  408),  and  escapes  in  bubbles  at  the  side. 

At  the  Polytechnic,  since  its  incorporation  by  royal  charter  m  the  \  ear  u  , 


484 


PNEUMATICS. 


Fig.  408.  —  The  Mouse  under  Water. 

The  mouse  in  a  bell-jar,  a,  connected  by  a  flexible  pipe  with  the  purr.p,  b. 


two  8-inch  cylinder  air-pumps  have  supplied  the  diving-bell  with  air,  which  the 
late  lamented  chairman,  the  Rev.  J.  B.  Owen,  wittily  spoke  of  as  “  tolling  the 
knell  of  each  departing  shilling,”  the  price  of  admission  to  the  descending 
diving-bell. 

To  illustrate  the  principle  of  this  machine,  take  a  glass  tumbler,  plunge  it 
into  water  with  the  mouth  downwards ;  you  will  find  that  very  little  water  will 
rise  into  the  tumbler,  which  will  be  evident  if  you  lay  a  piece  of  cork  upon 
the  surface  of  the  water  and  put  the  tumbler  over  it ;  for  you  will  see  that, 
though  the  cork  should  be  carried  far  below  the  surface,  yet  its  upper  side  is 
not  wetted,  the  air  which  was  in  the  tumbler  having  prevented  the  entrance  of 
the  water;  but  as  the  air  is  compressible,  it  cannot,  when  condensed,  entirely 
exclude  the  fluid. 

The  first  diving-bell  of  any  note  was  made  by  Dr.  Halley,  and  is  most  com¬ 
monly  seen  in  the  form  of  a  truncated  cone,  the  smallest  end  being  dosed, 
and  the  larger  <  ne  open.  It  is  weighted  with  lead,  and  so  suspended  that  it 
may  sink  full  of  air,  with  its  open  base  downwards,  and  as  near  as  may  be 
parallel  to  the  horizon,  so  as  to  be  close  with  the  surface  of  the  water.  Mr. 
Smeaton’s  diving-bell  was  a  square  chest  of  cast  iron,  4^  ft.  in  height,  4!  ft.  in 
length,  and  3  ft.  wide,  and  affording  room  for  two  men  to  work  in  it.  It  was 
supplied  with  fresh  air  by  a  forcing-pump.  This  was  used  with  great  success 
at  Ramsgate.  Other  contrivances  have  been  used  for  diving-bells. 

The  first  diving-bell  we  read  of  in  Europe  was  tried  at  Cadiz,  by  two  Greeks, 
in  the  presence  of  Charles  V.  and  ten  thousand  spectators.  It  resembled  a 
large  kettle  inverted.  The  first  person  who  brought  the  diving-bell  into  vogue 
with  us  was  Phipps,  an  American  blacksmith,  in  the  reign  of  Charles  II.,  and 
who,  from  the  fortune  he  acquired  from  a  Spanish  ship,  to  which  he  went 
down,  laid  the  foundation  of  the  honours  of  the  Mulgrave  family. 


THE  DIVING-BELL. 


485 


The  diving-bell  in  the  Great  Hall  at  the  Polytechnic  i~  composed  of  cast 
iron,  open  at  the  bottom,  with  seats  around,  and  is  of  the  we  ght  of  thr'e  tons  ; 
the  interior,  for  the  divers,  is  lighted  by  openings  in  the  crown  of  thick  plate 
glass,  which  are  firmly  secured  by  brass  frames  screwed  to  '.he  bell;  it  is  sus¬ 
pended  by  a  massive  chain  to  a  large  swing  crane,  with  a  powerful  crab,  the 
windlass  of  which  is  grooved  spirally,  and  the  chain  passes  four  times  over  it 
into  a  well  beneath,  to  which  chain  is  suspended  the  compensation  weights; 
and  it  is  so  accurately  arranged  that  the  weight  of  the  bell  is  at  all  depths 
counterpoised  by  the  weights  acting  upon  the  spiral  shaft.  The  bell  is  sup¬ 
plied  with  air  from  two  powerful  air-pumps,  of  8-inch  cylinder,  conveyed  by 
the  leather  hose  to  any  depth.  The  bell  is  put  n  o  action  several  times  daily; 
and  visitors  may  safely  descend  r.  considerab'e  d-pth  into  the  tank,  which, 
with  the  canals,  holds  nearly  ten  thousand  gallons  o  water,  and  which  can,  if 
required,  be  emptied  in  less  than  one  minute. 

Messrs.  Heinke’s  diving-helmet  and  diving-dress  have  been  in  use  at  the 
Polytechnic  for  many  years,  and  have  been  lectured  on  over  and  over  again. 
Perhaps  the  best  accoun'  of  these  lectu-es  anc.  other  new  facts  is  that  given 
by  the  “  Builder’s  ”  Weekly  Reporter  : 

“The  requirements  in  diving  apparatus  are  a  good  and  regular  supply  of 
air,  ability  to  see  clearly,  freedom  of  action  n^d  from  too  great  pressure  of 
the  incumbent  water,  proper  weighting  of  the  diver,  dryness  without  unpleasant 
tightness  of  apparel,  non-liability  to  disarrangement  in  th '  machinery,  facilities 
to  find  your  way  back  to  the  ship’s  communication,  a  perfect  code  of  signals, 
and  independent  air  provision  for  some  time  in  case  of  accident  to  the  air-hose. 
The  Messrs.  Heinke,  submarine  engineers,  0.  79  Great  Portland  Street,  W., 
have  made  it  a  life-long  study  to  improve  in  every  way  the  dresses  and  other 
apparatus  required  in  under-water  labour,  and  have  eminently  succeeded  in 
their  aim.  Passing  thoughtfully  by  Borelli’s  flotatory,  submarine,  and  con¬ 
densing  apparatus,  Halley’s  truncated  wooden  cone,  Rowe’s  diving-engine, 
Bushnell’s  tortoise-shell  contrivance,  Martin’s  similar  development,  &c.,  this 
eminent  firm  has  narrowly  watched  and  estimated  the  defects  in  each,  duly 
conecting  them.  The  submarine  dress  manufactured  and  exhibited  at  the 
Great  Exhibition  in  Hyde  Park,  in  1851,  obtained  the  award  of  a  prize  medal; 
and  since  that  period  other  improvements  have  been  effected,  as  their  want 
was  made  known,  the  Heinke  apparatus  being  now  considered  almost  perfect ; 
indeed,  in  its  use,  danger  to  life,  or  even  distress  of  feeling,  is  rarely  expe¬ 
rienced  by  divers  in  the  possession  of  ordinary  healti  Among  the  most  pro¬ 
minent  of  the  improvements  is  that  of  the  eye-frame,  to  which  is  attached  a 
brass  slide,  so  contrived  that,  in  case  of  accident  to  the  glass,  the  diver  can 
immediately  close  the  eye-hole,  and  thus  save  himself  from  drowning  an  c\  ent 
that  has  more  than  once  happened  where  Messrs.  Heinke’s  contrivance  w  as  ab¬ 
sent.  Submersion  or  ascension  to  any  degree  is  also  rendered  attain  a  >le  at  u  1 
by  the  introduction  of  a  double  valve  in  the  front  of  the  g')r£j£t :  t‘lc  "  e'^  u  0 
the  whole  apparatus  ♦hus  raised  being  upwards  of  200  lb.  he  great  eatun. 
of  all  these  improvements  is  that  they  place  the  apparatus  under  t  K  <-‘,n  10 
of  the  diver,  who  surely  must  be  the  best  judge  of  his  own  needs  ant  a  mgs. 
Thus,  in  the  event  of  unforeseen  casualty,  say  to  the  air-hose,  theie  ^  provi¬ 
sion  made  for  a  few  minutes’  supply,  as  a  reserve,  before  the  consump  ion 
which  the  diver  will  have  had  ample  time  to  reach  the  sui  face,  ut  t  r  c  iai  1 1 
of  accident  to  the  ordinary  hose-screw  have  been  lessened  bv  u  aPP.lca  ‘ 
of  a  double  safety-cap,  which  it  is  almost  impossible  to  biea  ..  ns  [  < 


486 


PNEUMATICS , 


renders  the  valve  at  the  back  of  the  helmet  less  indispensable,  making  the  hel¬ 
met  a  ‘  loose  ’  one  for  many  purposes.  The  connecting  joints  of  the  apparatus 
are  also  of  first-class  material  and  manufacture.  These  are  very  important 
parts  of  the  whole,  for  great  strength,  yet  ease  of  removal,  is  here  needed  in 
the  face  of  every  adverse  condition.  Messrs.  Heinke  fit  all  their  joints,  as  the 
hose-screw,  with  double  safety-caps,  and  make  them  resist  tne  most  powerful 
pressure.  Their  new  vulcanized  band  completely  excludes  the  water  from  the 
dress,  and  enables  it  to  fit  more  easily,  and  v/ith  greater  comfort  to  the  wearer. 
In  cold  weather  the  leather  band  used  formerly  became  hard,  and  could  not 
be  depended  t  n ;  while  the  vulcanized  band  is  totally  unaffected  by  atmo¬ 
spheric  change  or  ordinary  variations  of  temperature.  Their  signal-dial  is  a 
most  simple  yet  perfect  arrangement,  by  which  the  wants  of  the  diver  are  in¬ 
stantly  and  correctly  made  known  to  those  on  the  attendant  vessel.  Thus,  much 
time  will  be  saved  in  the  execution  of  the  more  important  and  massive  under¬ 
takings.  Of  course,  a  diver  prefers  to  main,  in  his  equilibrium  cither  under 
the  water  or  on  the  land ;  but  this  luxury  could  not  always  be  indulged  in 
under  former  arrangements.  The  old  helmet  and  spencer  were  merely  tied 
round  the  waist,  and  the  water  frequently  got  in;  whereas,  with  Messrs. 
Heinke  s  improved  vulcanized  banu,  th  diver  may  turn  a  complete  somer¬ 
sault,  and  yet  the  water  not  get  beneath  his  dress.  The  front  valve  in  the 
helmet  (before  referred  tc)  is  very  important  in  its  consequences,  as  it  enables 
the  diver  to  regulate  the  escape  of  air  and  his  speed  of  ascent  to  the  surface. 
With  the  escape-valve  behind  only,  the  diver  was  dep  ndenton  the  apparatus: 
if  that  worked  bafily,  or  the  air-pumps  were  laboured  too  fast,  and  the  escape- 
valve  behind  let  the  air  out  t  slowly,  the  dress  might  get  puffed  out,  and, 
like  pride,  receive  a  shock  at  the  moment  of  triumph, — the  diver’s  heels  be¬ 
coming  light  or  than  his  head,  and  his  entire  bociy  more  buoyant  than  the 
water,  so  rising  tv  its  surface  heels  uppermost !  This  cannot  occur  with  the 
use  of  the  front  valve.  The  diving-pump  will  throw  water  and  air  at  the  same 
time  through  distinct  hoses,  the  air-chamber  being  divided  or  separated  at  will. 
By  this  means,  the  diving-pump  can  be  used  for  extinguishing  fire  in  ships  or 
other  confined  places.  The  diver  being  supplied  with  fresh  air,  and  the  dress 
being  nearly  fire-proof,  the  diver  can  enter  any  place  on  fire  without  fear  of 
suffocation.  Thus  it  is  a  fire-engin:  and  d'ving  apparatus  combined.  The 
depth  of  the  diving-helmet  breastp.ate  is  increased  so  that  it  will  cover  the 
chest  and  the  region  of  the  lungs,  and  keep  off  the  pressure  in  deep  water 
Tim  submarine  lamp  will  burn  eight  hours  under  water,  and  is  supplied  with 
air  from  the  same  pump  as  supplies  the  diver.  The  patent  is  dated  1862,  in  the 
name  of  Mr.  C.  E.  Heinke,  and  a  helmet  dress  and  apparatus  made  in  ac¬ 
cordance  therewith  was  placed  in  Class  10,  International  Exhibition,  1862, 
where  it  claimed  considerable  attention. 

“  Many  trials  of  the  Messrs.  Heink^’s  apparatus  have  been  made,  and  with 
eminent  success.  The  experiments  conducted  at  Portsmouth,  in  June,  1855, 
in  presence  of  the  admiral  superintendent  and  dockyard  officers,  gave  great 
satisfaction,  the  diver  remaining  half  an  hour  at  a  time  in  seven  fathoms  of 
water.  At  Chatham  Dockyard,  in  October,  a  similar  successf  ul  trial  occurred 
before  distinguished  company.  P  has  been  tested  on  the  Seine  at  Paris,  under 
Government  command  and  supervision,  and  out  of  five  kinds  of  apparatus 
was  the  one  selected  as  the  beet, — the  French  exhibitor,  M.  Ernoux,  consi¬ 
dering  it  really  perfect !  At  the  Paris  Industrial  Exhibition  it  received  a  first- 
class  medal.  We  also  quote  the  following  from  ‘  The  Times’: 


HEINKES  DIVING-DRESS. 


487 


“  August  23,  i860:  :  Letters  this  morning  from  Point  de  Galle  announce  that 
the  whole  of  the  specie  of  the  Malabar — about  ,£280,000 — has  been  reco¬ 
vered.  The  diving  apparatus  used  was  Heinke’s  patent.’ 

“September  5,  i860:  ‘The  whole  of  the  diving  apparatus  in  use  by  the 
Royal  Engineers  at  Chatham  is  to  be  fitted  with  Mr.  Heinke’s  improved  eye- 
plates.’ 

“January  24.  1863  :  ‘The  whole  of  the  mails  and  cargo  have  been  removed, 
by  Heinke’s  diving  apparatus,  from  the  wreck  of  the  Colombo.  This  appa¬ 
ratus,  besides  its  utility  in  the  case  of  wreck,  is  in  the  case  of  fire  even  more 
valuable.  Protected  by  it,  persons  can  advance  with  per  ect  safety  through 
the  most  dense  smoke,  and  obtain  an  access  to  the  actual  source  of  mischief — 
an  advantage  on  board  ship  of  incalculable  importance.’ 

“  Perhaps  few  of  us  consider  the  many  uses  to  which  diving  apparatus  may 
be  put  in  the  years  to  come;  but  it  is  to  firms  like  the  one  under  considera¬ 
tion  that  we  must  look  for  the  initiative.  With  an  eye  on  the  alert  for  tokens 
of  usefulness  in  the  distant  future,  the  uses  of  the  present  will  be  probably  ere 
long  considerably  multiplied,  rendering  easy  many  now  difficult  undertakings. 
All  floating  structures,  those  having  their  foundations  beneath  the  waters, 
others  entirely  submerged  (be  they  constructed  by  man  or  God,  formed  of 
rock  or  vegetation),  may  be  repaired,  blasted,  cut  away,  built,  or  in  any  way 
operated  on  by  the  use  of  diving  apparatus.  Of  what  use  it  may  be  made  in 
war  we  know  not ;  but  in  the  interests  of  peace  its  conquests  may  be  many 
and  important.  From  the  latter  end  of  the  twelfth  century  to  the  present,  the 
mind  of  at  least  some  portion  of  the  engineering  world  has  ever  been  intent 
on  the  discovery  of  improvements  in  diving  apparatus  for  the  more  easy  pro¬ 
secution  of  submarine  labour.  The  necessities  of  ocean,  but  especially  her 
treachery, — the  strong  waves  and  contending  currents  hurrying  to  destruction 
on  the  land,  or  sinking  in  the  gulfs  beneath,  the  richest  argosies  of  wealth, — 
have  led  inventive  genius  to  special  effort  in  this  behalf.  To  Roger  Bacon  has 
been  attributed  the  origin  of  the  diving-bell ;  and  from  his  day  the  path  of 
improvement  can  be  variously  traced.  The  Emperor  Charles  \  .  is  reported 
to  have  witnessed  public  trials  made  with  what  Schott,  in  15645  called  ‘  an 
aquatic  kettle.’  In  1588,  a  sunken  vessel — one  of  the  celebrated  Spanish 
Armada — was  surveyed  by  this  means ;  and  thenceforward  Debrell,  Bishop 
Wilkins,  Borelli,  Phipps,  Triewald,  Smeaton,  and  the  Messrs.  Braithwaite 
experimented  in  this  department  of  useful  science,  meeting  with  obstacles 
and  overcoming  them ;  developing  for  the  apparatus  fresh  means  ot  useful¬ 
ness,  then  fitting  it  to  the  occasion.  By  the  end  of  the  sixteenth  century,  im¬ 
provement  had  made  rapid  and  decidedly  useful  and  paying  progress ;  for 
enormous  amounts  of  property  had  before  that  time  been  rescued  froni  sunken 
vessels,  and  improvers  in  diving  apparatus  had  been  already  honoured  In  our 
Government.  The  time  had  then  to  arrive  for  such  thorough  operations  as  to 
necessitate  the  diver  treading  the  floor  of  the  sea,  to  labour  there  as  on  ant , 
with  thought,  energy,  and  skill,  and  an  amount  of  accuracy  all  the  mon.  per¬ 
fect  as  the  submarine  work  committed  to  his  charge  would  lie  more  ca  amitous 
in  its  failure  than  the  destruction  of  any  mere  land  structure.  Hit  n  no  t;n 
descent  had  but  been  into  the  interior  of  submerged  vessels,  to  scan  1  or 
treasure,  or  into  caves,  no  great  weight  of  water  having  thus  to  oe 
Triewald  (before  alluded  to)  is  said  to  have  been  the  first  experiments!  in  ^  .e 
extended  sphere  of  operations,  and  to  have  introduced  convex  lenses  insteac  o 
plain  glass.  Now  followed  air-condensation,  and  the  necessari  appara  us 


488 


PNEUMATICS. 


improved  and  re-improved;  and  great  engineering  works  were  erected,  sur¬ 
veyed,  and  repaired,  so  that,  in  fact,  diving  operations  at  once  took  their  stand 
among  the  ‘  necessities.’  The  noble  Plymouth  Breakwater  had  its  firm  and 
solid  under-water  masonry  laid,  stone  after  stone,  by  the  aid  of  the  new  science. 
Other  great  works  followed;  the  ramifications  of  the  new  science  were  extended 
to  less  important  tasks,  and  now  there  are  few  under-water  operations,  in 
ocean,  river,  or  stream — to  found,  destroy,  or  prune — that  may  not  be  accom¬ 
plished  by  the  diver,  properly  equipped.  The  original  outlay  or  daily  main¬ 
tenance  is  not  so  great  as  to  necessarily  preclude  the  use  of  diving  apparatus 
in  small  works,  where  thorough  efficiency  and  economy  of  time  are  desired. 
We  hope  that  the  efforts  of  the  Messrs.  Heinke  in  the  way  of  improvement 
will  yet  at  no  distant  day  render  submarine  labour  but  little  more  difficult, 
laborious,  or  expensive  than  ordinary  avocations  on  land.” 

The  foregoing  accoun:  is  usefully  supplemented  with  the  following  extracts 
from  the  “  Reports  cf  the  International  Jury  of  the  Paris  Exhibition  of  1855, 
on  C  E.  Heinke  s  Diving  Apparatus:” 

“  Class  XIII.  (Marine) — Diving  Machines  and  Apparatus.  —Whilst  the 
loose  diving-dress  of  M.  To uboulic  may  be  taken  to  represent  the  elements  of 
the  art  of  diving,  the  different  apparatus  due  to  MM.  E.  Heinke,  Siebe,  Ca- 
birol,  and  Ernoux  realize,  on  the  contrary,  its  latest  improvements.  They  are 
all  identical  in  principle,  and  consiot  of  a  waterproof  dress,  with  a  metal  collar, 
on  which,  by  means  of  screws,  is  fastened  r.  metal  helmet,  provided  with  an 
air-pipe  which  receives  its  supply  from  a  pump  placed  on  the  deck  when  the 
diving  takes  place  from  a  vessel,  or  on  the  edge  of  the  pit  when  the  operation 
is  to  be  effected  on  shore.  Covered  with  this  dress,  the  diver  descends  to  any 
depth  that  may  be  desired.  In  these  apparatus  the  principal  conditions  to  be 
considered  are  — the  impermeability  of  the  dres;  itself,  its  resistanc  to  the 
pressure  of  the  water,  the  continued  renewal  of  fresh  air,  and  the  providing 
the  diver  .vith  the  means  of  seeing  while  at  work,  and  of  communicating  with 
the  surface  by  a  simple  and  certain  system  of  signals. 

“MM.  E.  Heinke  and  Siebe  have  found  means  of  providing,  between  the 
dress  and  the  body  of  the  diver,  for  the  introduction  and  retention  of  a  suffi¬ 
cient  quantity  of  air  to  insure  a  proper  amount  of  resistance  to  the  water, 
and  to  keep  the  body  in  an  atmosphere  of  which  the  elasticity  is  always  the 
same.  To  effect  this  they  inject  by  the  air-hose  a  greater  quantity  of  air  than 
escapes  by  the  valve  ir.  the  helmet  which  gives  issue  to  the  foul  air  and  that 
in  excess. 

“  Indeed,  Mr.  E.  Heinke  has  made  in  this  respect  a  remarkably  happy  im¬ 
provement  by  his  double-action  valve.  The  outside  of  the  valve  is  furnished 
with  a  slide,  which  opens  or  hermetically  closes  at  the  will  of  the  diver.  When 
the  valve  is  shut  the  dress  becomes  inflated  by  the  excess  of  air  pumped  in: 
the  diver  is  thus  rendered  lighter  than  the  water,  and  he  consequently  rises  at 
once  and  without  trouble  to  the  surface.  Should  there  be  any  danger  at  the 
bottom,  or  should  the  signal  have  failed  or  have  not  been  promptly  attended  to, 
the  diver  can,  by  regulating  his  valve,  immediately  rise  to  the  surface  and  give 
the  information  himself.  This,  indeed,  lately  occurred  in  the  Black  Sea,  on 
board  the  steam  corvette  the  Primauguet,  under  the  command  of  Captain 
Reynaud.  Mr.  Heinke’s  diver  has  thus,  by  regulating  the  valve,  the  power  of 
sinking  as  slowly  as  he  thinks  proper,  while  the  other  divers,  dragged  down 
by  the  enormous  weights  placed  upon  their  shoulders  to  insure  their  immer- 


OTHER  DIVING-DRESSES. 


489 


sion,  are  compelled  to  remain  at  the  bottom  till  drawn  up  by  the  cord  attached 
to  their  sides. 

“  The  apparatus  of  M.  Ernoux  is  not  so  complete.  The  diver  who  uses  this 
apparatus  is  not  protected,  as  in  that  of  Mr.  E.  Heinke,  by  the  introduction  of 
air  inside  the  dress.  Instead  of  escaping  by  the  valve  in  the  helmet,  the  air 
is  at  once  forced  out  (without  being  able  to  penetrate  the  dress)  by  the  holes 
arranged  for  that  purpose  between  the  metal  collar  and  the  top  of  the  dress. 
The  dress  is  thus  continually  in  immediate  contact  with  the  body,  for  between 
it  and  the  water  which  compresses  it  there  is  only  the  thickness  of  a  non¬ 
elastic  stuff.  Without  attempting,  therefore,  to  fix  the  exact  limit  of  depth  at 
which  this  dress  will  permit  to  work,  we  may  nevertheless  affirm  that  Mr.  E. 
Heinke’s  diver  will  be  able,  if  necessary,  to  work  with  ease  at  a  depth  where 
the  diver  of  M.  Ernoux  could  not  remain  without  danger  of  suffocation. 

“  In  all  the  different  systems  the  diver  receives  the  light  through  lenses  of 
glass  or  crystal,  placed  in  front  of  the  helmet;  but  this  is  so  far  dangerous  that, 
if  the  glass  happens  to  break,  the  water  rushes  in  and  suffocates  the  diver. 
Mr.  E.  Heinke  is  the  only  one  who  has  -bviated  the  danger  arising  from  this 
cause.  If  the  glass  of  his  helmet  breaks,  the  diver  immediately  shuts  the 
escape- valves,  and  the  air  rushes  out  through  the  broken  glass — the  only 
means  by  which  it  can  escape— and  thus  prevents  the  entrance  of  the  water. 
The  diver  may  even  descend  with  a  broken  glass,  and  yet,  by  the  remarkable 
improvement  introduced  by  Mr.  E.  Heinke,  he  may  remain  submerged  with¬ 
out  impediment,  and  continue  the  operations. 

******* 

“We  have  only  said  a  few  words  en  passant  of  M.  Siebe.  His  apparatus 
is  the  same  as  that  of  Mr.  E.  Heinke,  but  without  the  improvements  we  have 
pointed  ou'  ;  but  the  priority  in  the  construction  of  this  class  of  apparatus— 
which  in  itself  is  a  very  great  merit — seems  to  belong  to  him.  However  this 
may  be,  the  problem  of  diving  apparatus  seems  to  us  to  be  now  practically 
solved.  They  will,  doubtless,  be  still  further  improved;  but,  such  as  they  are, 
they  are  sufficient  for  the  examination  of  the  bottoms  of  vessels  and  of  screws  at 
sea,  and  they  will  be  principally  employed  for  these  two  purposes  by  the  navy, 
and  for  all  kinds  f  submarine  operations.” 

An  award  of  a  first-class  medal  was  therefore  made  to  Mr.  C.  E.  Heinke, 
because  his  diving  apparatus  was  considered  the  most  perfect  of  the  kind 
which  has  been  produced  up  to  the  present  time. 

“The  principal  improvement  which  he  has  introduced  consists  in  enabling 
the  diver  to  remain  under  water  when  an  accident  occurs,  such  as  the  bieak- 
ing  of  a  glass,  which  would  otherwise  have  allowed  the  water  to  penetrate  into 
the  dress.  ' — Vol.  II.,  p.  41. 

Again,  it  is  stated—  _  „  .  , 

“Class  XIV. — Constructions  Ciyiles. — In  the  apparatus  of  Mr.  E.  Heinke 
the  valve  is  placed  o  the  chest,  and  the  diver  can  enclose  it  with  his  ham  at 
pi  asure  if  any  portion  f  his  dress  is  torn  while  at  work  :  the  cuijent  ot  an 
then  becomes  directed  towards  the  opening,  and  the  diver  is  enabled  to  ascend 
j  without  danger.” — Vol.  II.,  pp.  197,  198. 

A  patent  has  lately  been  secured  by  Messrs.  Alfred  and  Joseph  lyler,  0 
|  Newgate  Street,  London,  for  “  Improvements  in  Arrangements  and  Appa- 
!  ratus  for  Use  in  Submatine  Operations,”  by  which  the  diver  is  enablec  to 
work  with  facility  in  very  deep  water  by  reducing  the  pressure  on  the  10c  \ 
and  limbs.  The  inventors  employ  a  framework  skeleton  or  armour,  loi  uu  <- 


49° 


PNEUMATICS. 


out  of  metal,  to  envelope  or  encircle  the  body,  arms,  and  legs  of  the  diver, 
which  extends  or  comes  up  to  that  part  where  the  metal  helmet  usually  rests. 
Over  this  armour  is  placed  the  water-tight  dress.  Another  improvement  is 
in  the  reduction  of  the  pressure  of  air  to  be  breathed  by  removing  the  escape- 
valve  to  a  point  nearer  the  surface  of  the  water,  and  also  an  ingenious  mode 
of  preventing  the  deposit  of  moisture  on  the  inside  of  the  glass  window  of  the 
diver’s  helmet  by  directing  a  spray  or  current  of  air  over  it.  It  is  fully  ex¬ 
pected  that  successful  experiments  in  very  deep  water  will  be  made  with  this 
new  apparatus. 

The  inventors  state  that  their  invention  has  for  its  object  improvements  in 
arranging  submarine  or  diving  apparatus,  whereby  the  same  is  enabled  to  be 
used  with  greater  facility  and  convenience  for  respiration  and  working  in  deep 
water  than  is  the  case  with  the  apparatus  ordinarily  used  for  this  purpose, 
and  also  to  afford  a  means  of  reducing  the  pressure  on  the  body  and  limbs 
of  the  diver  when  equipped  in  the  same,  and  descending  below  the  surface  of 
the  water,  so  that  he  may  work  in  deeper  water  than  usual,  under  the  pressure 
due  to  a  less  depth,  and  relates  to  formation  and  arrangement  of  armour  for 
the  body  and  limbs  of  the  diver,  and  the  parts  connected  therewith,  and  the 
arrangement  of  pipes,  tubes,  valving,  and  other  parts  to  be  used  in  connection 
with  diving  apparatus.  “We  employ  a  framework  skeleton  or  armour,  formed 
of  metal  or  other  suitable  material,  which  may  be  formed  of  separate  pieces 
or  parts  embedded  in,  or  covered  with,  india-rubber  if  desired,  and  riveted 
or  flexibly  connected  together  throughout,  or  in  parts  if  desired,  or  of  metal 
rings,  spirals,  or  hoops,  and  arranged  so  as  to  encircle  the  body,  arms,  and 
legs  of  the  diver,  and  extend  to  the  position  where  the  helmet  usually  rests. 
Over  this  metal  or  armour  the  water-tight  dress  of  the  diver  may  be  placed, 
and  a  similar  dress  or  lining  may  be  attached  to  the  interior  of  the  armour 
between  them,  or  the  dress  itself  may  be  formed  of  sufficient  thickness  to 
produce  the  same  results. 

“  In  order  that  signals  or  instructions  may  be  transmitted  to  the  diver  whilst 
below  the  surface  of  the  water,  and  to  render  it  unnecessary  for  him  to  ascend 
to  the  surface  to  receive  them,  we  employ  a  separate  tube  attached  to  the 
dress  or  armour,  and  connected  with  a  suitable  auditory  apparatus,  and  so 
arranged  that  neither  air  nor  water  can  pass  through  the  tube  and  get  into  the 
dress  ;  and  by  speaking  into  the  open  end  which  is  above  the  surface  of  the 
water,  the  diver  will  be  able  to  hear  the  message  whilst  below  the  water. 

“  In  order  that  the  glasses  through  which  the  diver  sees  may  be  kept  free 
from  dust,  or  the  condensation  of  moisture  which  occurs  when  the  apparatus 
is  used,  we  cause  a  jet  or  spray  of  fresh  air,  entering  the  helmet,  to  pass  over 
these  glasses  by  arranging  the  inlet  passages  from  the  air-tube  with  a  slot  or 
opening  placed  at  the  required  angle  to  do  this,  and  thus  add  to  the  conveni¬ 
ence  of  the  apparatus.  ’ 

The  novelties  claimed  are: 

First,  the  formation  of  parts  forming  the  apparatus  to  diminish  the  pres¬ 
sure  on  the  body  of  the  diver,  and  also  to  allow  him  to  breathe  more  freely. 

Second,  embedding  the  protective  metal  armour  in  flexible  air  and  water¬ 
proof  material. 

Third,  the  addition  of  an  extra  valve  to  the  inlet  pipe. 

Fourth,  the  application  of  auditory  apparatus. 

Returning  to  the  exhausting  air-pump,  a  number  of  experiments,  illustrating 
the  weight  of  the  atmosphere,  may  be  demons  I  rated. 


EXPERIMENTS  WITH  THE  AIR-PUMP. 


491 


EXPERIMENTS  WITH  THE  AIR-PUMP. 

Two  brass  hemispheres,  nicely  fitting  together,  with  ground  edges  gi eased, 
may  be  easily  separated ;  but  directly  they  are  joined  and  screwed  on  the 
air-pump,  which  is  then  set  in  motion,  it  will  he  found  that  in  pumping  out 
the  air  from  the  inside  a  pressure  is  brought  to  bear  upon  the  outside ;  and  if, 
after  exhaustion,  the  brass  sphere,  usually  called  “the  Magdeburg  hemi¬ 
spheres,”  are  unscrewed  from  the  air-pump  plate,  and  handles  put  on,  it  will 
be  found  that  two  men,  pulling  one  against  another,  will  rarely  separate  the 
hemispheres,  which  are  pressed  together  with  a  force  of  nearly  200  lb.,  suppo¬ 
sing  the  hemispheres  are  of  a  diameter  of  four  inches.  When  a  membrane 
is  stretched  over  one  of  the  mouths  of  a  cylindrical  glass  open  at  eacii  end, 
and  the  other  is  greased  and  placed  on  the  air-pump  plate,  the  first  stroke 


F IG.  409.  —  The  Magdeburg  Hemispheres.  Fig.  410. 


of  the  pump  causes  the  membrane,  which  should  be  dry,  to  take  a  concave 
form,  and  if  the  air-pump  is  now  rapidly  worked,  the  pressure  of  the  u  to  t 
outer  column  of  air,  of  a  diameter  equal  to  that  of  the  membrane,  is  btougi 
to  bear  upon  it,  which  ultimately  breaks  in  the  bladder  with  a  loud  noise.  •-  s 
the  air  exerts  a  pressure  of  15  lb.  upon  every  square  inch,  the  bursting  in  o 
the  membrane  is  not  very  surprising.  .  , 

To  prove  that  an  exhausted  receiver  is  held  down  by  the  pret>suie  o  10 
air,  take  one  open  at  the  top,  and  ground  quite  flat,  as  at  f  ig.  4i-»  an'.cm  uu 
with  a  brass  plate,  which  has  a  brass  rod  passing  through  't,  uor'ing  u 
collar  of  leather,  so  as  to  be  air-tight.  To  this  rod  suspend  a  sma  rcui 
within  the  larger  one,  a  little  way  from  the  bottom.  Place  the  outri  re  ei 
on  the  air-pump,  and  exhaust  it:  it  will  now  be  fixed  fast  down  ,  u  e 
receiver  may  be  pulled  up  or  down  with  perfect  ease,  as  it  is  itse  ex  <  » 

and  all  the  air  which  surrounded  it  removed,  consequenth  it  canno  v  ■ 
posed  to  any  pressure.  Let  then  the  small  one  down  upon  the  plate,  but  not 
over  the  hole  by  which  the  air  is  extracted,  and  re-adnut  1 10  an  1 


492 


PNEUMATICS. 


larger  receiver,  which  may  then  be  removed ;  it  will  be  found  that  the  small 
one,  being  itself  exhausted,  is  held  down  fast  by  the  air  which  is  now  admitted 
round  the  outside.  If  the  large  receiver  be  again  put  over  it,  and  exhausted, 
the  small  one  will  be  at  liberty;  and  so  on,  as  often  as  the  experiment  is 
repeated. 

“  This  effect,”  says  Imison,  who  relates  the  above  careful  experiment,  “  can¬ 
not  be  accounted  for  upon  any  other  principle  than  the  pressure  of  the  air,  as 
the  common  idea  of  suction  can  have  nothing  to  do  in  the  case  of  the  small 
receiver,  which  is  fixed  down  merely  by  letting  in  the  air  around  it.  We  ought, 
therefore,  to  attribute  all  those  effects  which  are  vulgarly  ascribed  to  suction, 
such  as  the  raising  of  water  by  pumps,  &c.,  to  the  weight  and  pressure  of  the 
atmosphere.” 

A  column  of  mercury,  29!  in.  high  and  1  in.  square,  weighs,  in  round  num¬ 
bers,  15  lb.;  consequently  the  air  presses  with  a  weight  equal  to  15  lb.  upon 
every  square  inch  of  the  surface  of  the  earth. 

Galilei  Galileo,  the  immortal  mathematician  and  astronomer,  the  legitimate 
offspring  of  Vincenzio  Galilei  and  Giulia  di  Corimo  Ammanali  di  Pescia,was  the 
first  who  discovered  the  gravitating  power  and  weight  of  the  air;  he  compared 
the  latter  with  that  of  water,  and  pronounced  it  to  be  impossible  to  raise  water 
higher  than  33  ft.  by  what  was  then  styled  suction.  He  proved  that  suction 
was  the  language  of  a  fable,  and  really 
meant  nothing;  and  that  the  rise  of 
water  in  a  pump,  expressed  in  sober,  phi¬ 
losophical  language,  was  not  “  the  power 
of  suction,”  but  “  the  pressure  of  the  airy 

The  pu^il  of  Benedetto  Castelli,  Evan- 
gilista  Torricelli,  another  learned  mathe¬ 
matician  and  philosopher  —  called,  in 
nearly  all  the  books,  a  pupil  of  Galileo, 
although  only  a  resident  with  the  latter  a 
few  weeks,  as  Galileo  died  three  months 
after  Torricelli  arrived  in  his  house — this 
disciple  of  Galileo,  reflecting  that  mer¬ 
cury  was  fourteen  times  heavier  than 
water,  considered  that  a  column  of  quick¬ 
silver  j1^  of  the  length  of  33  ft.  of  water 
ought  to  be  an  equal  balance  to  the 
latter;  and  hence  he  discovered  the  true 
principle  upon  which  the  barometer  is 
constructed. 

Torricelli  filled  a  glass  tube,  closed  at 
one  end,  and  about  3  ft.  in  length,  with 
mercury ;  then,  placing  his  finger  on  the 
open  end  of  the  tube  filled  with  mercury, 
he  inverted  it  in  a  basin  containing  the 
same  metal.  The  mercury  he  had  poured 
in  the  tube,  measuring  36  in.,  fell  imme¬ 
diately  to  the  height  corresponding  to  the 
then  pressure  of  the  air,  say  30  in.,  and 
the  space  above,  containing  nothing,  was 

called,  after  Torricelli,  the  “  1  orricellian  Fig.  41 1. — A  Weather-glass. 


THE  BAROMETER. 


493 


vacuum.”  The  30  in.  of  mercury  were  sustained  by  the  pressure  of  the  air, 
and  it  was  soon  discovered  that  the  fluid  metal  did  not  remain  stationary;  it 
varied  daily,  and  the  variations  appeared  to  precede  changes  in  the  weather, 
and  thus  gradually  it  came  to  be  called  the  weather-glass.  (Fig.  411.^ 


THE  BAROMETER. 


Two  Greek  works— /3rfpos,  a  weight,  and  perpov,  a  measure— are  enlisted 
give  the  title  to  this  most  valuable  instrument,  which  accurately  demon¬ 
strates  the  variability  of  the  pressure  of  the 
air.  Mercury  is  about  thirteen  times  heavier 
than  water;  consequently  a  column  of  mer¬ 
cury  1  in.  square  and  about  30  in.  in  height 
will  counterbalance  a  column  of  water  34  ft. 
high  and  1  in.  square  at  the  base,  or  both 
will  hold  in  equipoise  a  column  of  air  of  its 
natural  height  from  the  earth,  or  that  aerial 
mixture  which  is  supposed  to  be  included 
within  a  distance  of  45  miles  of  the  earth’s 
surface,  i.e.,  starting  from  the  level  of  the 
sea. 

The  specific  gravity  of  air  is  taken  as 
unity  or  one,  and  it  is  the  standard  writh 
which  the  density  of  all  gaseous  bodies  is 
compared.  Air  at  30  Bar.  and  320  Fahr.  is 
769^4  lighter  than  water,  and  10,462  times 
less  heavy  than  mercury. 

A  barometer,  for  rough  purposes,  is  soon 
made.  A  clean,  dry  tube  of  stout  glass, 
called  barometer-tube,  is  hermetically  sealed 
at  one  end;  pure  mercury  ir  then  poured  in 
until  the  tube  is  filled  within  one  inch  of  the 
open  end;  the  thumb  is  now  held  tightly 
over  the  latter,  and  the  air  included  in  the 
small  space  already  alluded  to  is  slowly 
passed  up  and  down  the  tube,  in  order  to 
collect  all  the  smaller  bubbles  of  air  which 
adhere  to  the  inside  of  the  glass  tube.  The 
tube,  filled  with  mercury,  is  left  standing  up¬ 
right,  and  is  gently  tapped  (say  daily  for  a 
week),  in  order  to  assist  the  escape  of  any 
bubbles  of  air.  It  is  then  inverted  in  a  basin 
of  clean  mercury,  and,  supposing  the  tube  to 
be  36  in.  in  length,  the  mercury  may  fall  to 
30  in.,  and  the  space  between  30  in.  and 
36  in.  is  called,  as  already  stated,  the  Torri- 

Fig.  412. —  The  Barometer  in  the  cellian  vacuum.  ,  , 

Vacuum  of  an  Air-Pump.  The  barometer  thus  made,  if  placet  unt 


494 


PNEUMATICS. 


the  receiver  of  an  air-pump  (Fig.  412),  indicates,  by  the  falling  of  the  mercury, 
the  amount  of  vacuum  procurable  by  any  pump  that  the  operator  may  wish 
to  test ;  and,  as  before  stated,  there  is  always  a  fractional  portion  left  behind, 
however  excellent  tire  air-pump  may  be.  A  pump  that  will  remove  329  vo¬ 
lumes  out  of  330  may  be  regarded  as  a  very  good  one. 

The  more  refined  instruments  required  for  meteorological 
purposes  are  made  in  the  same  manner,  with  the  additional 
precaution  of  boiling  the  quicksilver  in  the  tube,  so  as  to  get 
rid  of  the  last  bubbles  of  air.  It  is  this  which  renders  them 
more  costly,  as  many  tubes  are  sometimes  broken  in  the 
process  of  boiling.  There  are  many  good  barometer-makers 
in  London. 

Fig.  413  represents  a  refined  instrument,  made  by  Negretti 
and  Zambra,  who  give  the  following  instructions; 

A  Standard  Barometer,  on  Fortin’s  principle,  reading  from 
an  ivory  point  in  the  cistern,  to  insure  a  constant  level — with 
mercury  boiled  in  the  tube.  The  barometer-tube,  which  is 
-N  of  an  inch  diameter,  is  enclosed  and  protected  by  a  tube 
of  brass  extending  throughout  its  whole  length ;  the  upper 
portion  of  the  brass  tube  has  two  longitudinal  openings 
opposite  each  other;  on  ore  side  of  the  front  opening  is  the 
barometrical  scale  of  English  inches,  divided  to  show,  by 
means  of  a  vernier,  of  an  inch;  on  the  opposite  side  is 
sometimes  divided  a  scale  of  French  millimetres,  reading 
also  by  a  vernier  to  of  a  millimetre;  the  reservoir  or  cis¬ 
tern  of  the  barometer  is  of  glass,  closed  at  bottom  by  means 
of  a  leather  bag,  acted  upon  by  a  thumb-screw  passing 
through  the  bottom  of  an  arrangement  of  brass-work,  by 
which  it  is  protected.  A  delicate  thermometer  is  attached 
to  the  brass  tube. 

Directions  for  fixing  the  Barometer. — Having  determined 
upon  the  position  in  which  to  place  the  instrument,  fix  the 
mahogany  board  as  nearly  vertical  as  possible ;  and  ascer¬ 
tain  if  the  barometer  is  perfect,  and  free  from  air,  in  the 
following  manner:-  lower  the  screw  at  the  bottom  of  cistern 
three  or  four  turns,  that  the  mercury  in  the  tube,  when  held 
upright,  may  fall  two  or  three  inches  from  the  top;  then 
slightly  incline  the  instrument  from  the  vertical  position,  and 
if  the  mercury  in  striking  the  top  elicit  a  sharp  tap,  the  in¬ 
strument  is  perfect.  If  the  tap  be  dull,  or  not  heard  at  all, 
there  is  air  above  the  mercury,  and  must  be  driven  into  the 
cistern  by  inverting  the  insfi  ument ,  and  gently  tapping  it 
with  the  hand.  Supposing  the  barometer  to  be  in  perfect 
condition,  it  is  next  suspended  on  the  brass  bracket,  its  cis¬ 
tern  passing  through  the  ring  at  bottom  of  the  mahogany 
board,  and  allowed  to  find  its  vertical  position,  after  which 
it  is  firmly  clasped  by  means  of  the  three  thumb-screws. 

Before  making  an  observation,  the  mercuiy  in  the  cistern 
must  be  raised  or  lowered,  by  means  of  the  thumb-screw, 
until  the  ivory  point  and  its  reflected  image  are  just  in  con¬ 
tact;  the  vernier  is  then  moved  by  means  of  the  milled 


Fig.  413. 

A  Standard 
Barometer 


THE  BAROMETER. 


495 


head,  until  its  lower  termination  just  ex¬ 
cludes  the  light  from  the  top  of  the  mercurial 
column  ;  the  reading  is  then  taken  by  means 
of  the  scale  on  the  limb  and  the  vernier. 

A  very  excellent  and  moderate-priced  in¬ 
strument  is  that  made  by  Davis  and  Co.,  163 
Fcnchurch  Street.  (Fig.  414). 


Fig.  415. — Admiral  Fitzro/s  Storm-drum. 

A  Gale,  proIiaMv  fr<  m  nort'i. 

B.  Gal--,  probably  from  sou'll. 

c.  Expect  dangerous  winds  from  opposite  quarters  success¬ 
ively. 

D  Dangerous  wind  expected  from  nor'U. 
e.  Dangerous  wind  expected  from  south. 


Admiral  Fitzroy’s  name  is  attached  to  this 
instrument,  and  it  consists  of  the  barometer 
with  thermometer,  also  a  table  indicating  by 
the  rise  and  fall  of  the  mercury  the  direction 
of  the  approaching  winds,  with  Admiral  Fitz¬ 
roy’s  special  instructions  for  this  instrument. 
The  writer  was  inclined  to  suppose,  from  its 
low  price  of  fifty  shillings,  that  it  could  not 
be  very  accurate;  but,  on  comparing  the  in¬ 
strument  for  some  days  with  a  standard  ba¬ 
rometer,  it  was  found  to  be  very  sensitive, 
and  although  not  quite  agreeing  with  the 
standard  instrument,  was  sufficiently  near 
for  all  ordinary  purposes,  and,  with  the 


PNEUMATICS. 


496 


Fig.  416. —  The  Self-registering  Barometer  at  Stony  hurst  College. 

directions  inside  the  case,  renders,  as  the  late  Dr.  Herapath  said,  “  the  indica¬ 
tions  of  Davis’s  barometer  more  readily  intelligible  and  trustworthy;”  in  fact, 
weather-wisdom  has  been  thus  reduced  to  rules  of  comparative  certainty. 

At  Stonyhurst  College  (Fig.416),  also  at  Kew  and  other  places,  there  are  regu¬ 
lar  observatories  where  the  rise  and  fall  of  the  mercury  in  the  barometer  is 
automatically  registered  night  and  day. 

The  thermometer  is  also  registered  in  a  similar  manner;  likewise  the  direc¬ 
tion  and  velocity  of  the  wind. 

The  papers  on  which  the  rise  and  fall  of  the  barometer  are  registered  are 
called  “  barograms”  (Fig.  417) ;  those  of  the  thermometer  are  termed  “thermo¬ 
grams”  (Fig.  419) ;  and  the  papers  that  record  the  direction  and  force  of  the 
winds,  “anemograms”  (Fig.  420}.  -jui  I 

By  the  kindness  of  the  Rev.  S.  G.  Perry,  and  with  the  concurrence  of  the 
Rev.  Father  the  rector  of  Stonyhurst,  reduced  copies  of  all  these  are  appended, 
with  a  drawing  and  description  of  the  self-registering  barometer  (Fig.  416). 

A  b  (Fie.  416)  is  a  slate  slab  supported  on  two  stone  piers,  similar  to  those 
which  support  the  magnetographs.  C  is  the  clock  which  turns  the  cylinder 
D,  on  which  the  sensitive  paper  is  wrapped.  E,  a  lens  for  focusing  the  light 
which  passes  over  the  mercury  column  at  F.  G,  a  lens  for  condensing  the 
gas-light  H.  K  L  M  N  P  is  a  wooden  covering,  fitting  closely,  to  keep  any 
scattered  light  from  discolouring  the  paper  on  the  cylinder.  (£  R  is  a  level 
acted  upon  by  the  zero-temperature  rods,  which  run  parallel  to  the  baro¬ 
meter.  x  is  a  focusing-screw,  which,  when  once  fixed,  is  never  touched, 


THE  BAROMETER. 


497 


since  any  alteration  in  it  would  alter  the  constants  of  the 
curves. 

In  the  barogram  (Fig.  417),  the  straight  white  line  en¬ 
ables  the  observer  to  see  the  curve  of  the  upper  dark  one. 
showing  how  the  light,  which  acts  upon  the  paper  prepared 
by  a  photographic  process,  has  been  cut  off  by  the  rise  of 
the  mercury,  or  allowed  to  pass  when  the  latter  fell. 

Fig.  418  shows  how  the  curve  seen  at  Fig.  417  is  reduced 
to  figures  ;  part  only  of  a  barogram,  X,  is  shown.  This  is 


131 

80 

— 

<30 

— 

_ 

40 

20 

— 

30 

80 

E 

00 

. 

40 

— 

20 

~ 

2f> 

~ 

80 

- 

CO 

— 

-10 

20 

— 

28 

— 

80 

— » 

GO 

— 

40 

E 

20 

— 

22 

— 

' 

Fig.  417. 

Copy  of  a  Barogram 
from  Stony  hurst. 


Fig  41  ^ 

.-'2 


498 


PNEUMATICS. 


checked  by  an  ivory  scale,  z,  by  placing  A  B  of 
the  scale  z,  on  the  top  line,  C  D,  of  the  barogram 
X ;  then  the  reading  of  the  scale  at  the  line  M  N 
gives  the  height  of  the  barometer.  The  shaded 
portion  of  the  barogram  is  the  part  acted  upon 
by  the  line  of  light  which  passes  over  the  top  of 
the  column  of  mercury.  The  lens  in  front  of  the 
cylinder  inverts  the  whole,  pq  is  for  temperature 
corrections.  The  graduation  of  the  ivory  scale 
depends,  of  course,  on  the  constants  of  the  par¬ 
ticular  instruments  used. 

A  barometrical  observation  is  always  corrected 
for  capacity  and  temperature,  capillarity,  and  for 
the  index  error. 

The  following  directions  for  taking  an  observa¬ 
tion  of  the  barometer  are  given  in  Watt's  Dic¬ 
tionary 

1.  Read  and  correct  the  attached  thermometer, 
making  a  correction  for  index  error,  if  neces¬ 
sary. 

2.  Adjust  the  mercury  below  to  exact  contact 
with  the  fiducial  point. 

3.  Slightly  tap  the  tube  near  the  upper  end  of 
the  column,  and  adjust  the  edge  of  the  ver¬ 
nier  to  exact  tangential  contact,  the  line  of 
vision  being  horizontal. 

4.  Record  the  reading,  and  work  out  the  correct 
height  as  soon  as  convenient  afterwards,  as 
shown  in  the  following  example,  which  com¬ 
prises  all  the  corrections  ever  required : 


Attached  thermometer 
Data.  Neutral  point 
Capacity  . 

Diameter  of  tube  . 

Index  error  to  K.  O.  standard 
(apart  from  capillarity)  . 


Barometer  reading. 
Correction  for  capacity 
„  „  capillarity 


58-3°  F. 
28-861 » 

1 

3  3 

■4  in. 


—  -014  in. 

Inches 

29-964 
+  ’033 
+  •007 


temperature 
index  error 


30-004 

—  -080 

—  -014 


True  height  of  the  barometer 


29-910 


The  purchaser  of  a  barometer  for  scientific 
purposes  should  insist  on  receiving  with  it  an 


I.’ 


THE  BAROMETER. 


499 


authentic  certificate  of  its  index  error,  from  comparison  with  the  Greenwich, 
Kew,  or  Royal  Society’s  standard  barometer. 


32 — 2 


PNEUMATICS. 


For  meteorological  purposes,  the  observation  of  the  rise  and  fall  of  the 
thermometer  taken  with  that  of  the  barometer  is  of  considerable  importance, 
whilst  the  record  of  the  anemometer,  or  wind-gauge,  affording  anemograms 
(Fig.  420)  such  as  that  of  Ostler’s  self-registering  anemometer  with  the  rain- 
gauge,  represent  the  scientific  data  that  might  enable  observatories  to  give 
notice  of  approaching  storms,  especially  if  the  central  national  observatory 
receives  constant  telegrams  of  the  state  of  the  weather  from  all  parts  of  the 
world. 

More  experience  derived  from  carefully  conducted  observations  at  a  variety 
of  places  in  England  and  on  the  Continent  will,  no  doubt,  gradually  enable 
meteorologists  to  predict  with  absolute  certainty  that  which  Admiral  Fitzroy 
could  only  do  imperfectly  by  the  then  obtained  data  from  the  various  obser¬ 
vatories;  but  what  he.did  is  sufficiently  encouraging  to  induce  meteorologists 
all  over  the  world  to  remember  that  “  unity  is  strength  and,  by  exchanging 
barograms,  thermograms,  anemograms,  and  rain-gauge  heights,  they  can 
assist  each  other  in  forming  correct  calculations  of  the  general  weather  to  be 
expected  at  various  seasons  and  in  different  parts  of  the  world ;  they  can  also 
give  each  other  warning  of  the  probable  approach  of  any  great  currents  of  air 
or  wind,  and  thus  help  to  prevent  the  disastrous  wrecks  which  strew  the 
shores  of  the  various  countries  along  which  the  track  of  commerce  is  marked 
out. 

The  old-fashioned  wheel  barometer  (Fig.  41 1,  page  441)  is  still  a  great 
favourite,  because  “  those  that  run  may  read.”  Any  one  can  tell  the  weather, 
at  least  theoretically,  by  looking  at  its  honest  old  silver  face.  The  wheel  ba¬ 
rometer  means  well,  but  acts  somewhat  incorrectly,  because  it  works  by  the 
rising  and  falling  of  an  iron  counterbalanced  weight  floating  in  the  mercury; 
and  if  this  should  stick,  or  the  string  and  counterpoise  act  indifferently,  it  is 
extremely  disheartening,  after  settling  a  picnic  on  the  authority  of  the  “glass” 
stating  that  the  weather  is  not  only  “  set  fair,”  but  “  very  dry,”  to  discover,  just 
as  the  hampers  of  provisions  are  started,  and  the  new  bonnets  getting  into 
the  open  carriage,  that  the  weather  is  insolently  defiant,  and,  not  caring  a  bit 
about  what  the  wheel  barometer  says,  is  just  opening  a  “  nice  drizzle,”  •sure 
to  improve  into  a  steady  “downpour.”  It  is  better  to  get  a  Davis’s  two-guinea 
Fitzroy  barometer,  and  calculate  the  chances  of  weather  in  the  regular  way, 
viz.,  1st,  by  what  has  gone  before;  2nd,  temperature ;  3rd,  state  of  wind;  4th, 
steadiness  or  unsteadiness  of  the  barometer. 

The  Standard  Aneroid  Barometer  is  constructed  on  the  same  principles  as 
the  ordinary  aneroid,  but  with  extra  care  in  make  and  finish  to  ensure  greater 
freedom  of  motion,  hence  more  sensibility  and  accuracy  in  its  readings.  The 
divisions  on  the  dial  are  very  fine,  both  in  quality  and  space,  dividing  the  read¬ 
ing  to  a  hundredth  part  of  an  inch.  It  has  also  a  scale  indicating  the  pressure 
of  the  atmosphere,  of  the  following  range — from  1,000  ft.  below  to  7,000  ft. 
above  the  surface  of  the  earth.  It  is  very  portable,  will  act  in  any  position, 
and  is  not  liable  to  injury  in  transit. 

Its  construction  may  be  thus  described  : — A  nearly  flat  metal  box,  exhausted 
of  air,  the  upper  surface  or  lid  of  which  is  firmly  held  by  a  powerful  spring, 
connected  with  the  hands  by  means  of  a  lever  and  chain,  thus,  as  it  were, 
multiplying  the  small  motion  of  the  pressure  of  the  air  by  giving  an  extended 
reading  on  the  margin  of  the  dial.  At  the  back  of  the  instrument,  a  screw- 
head  is  visible,  which,  if  slowly  and  carefully  turned,  will  enable  the  aneroid 
to  be  adjusted  to  a  mercurial  standard  barometer. 


THE  BAROMETER. 


The  air  being  proved  to  be  material,  like  water,  it  was  not  long  before  the 
genius  of  man  said  he  ought  to  be  able  to  swim  in  air  as  well  as  in  water,  or, 
in  plainer  terms,  to  fly. 

Daedalus  essa\ed  the  task, 
and  h  iving  been  successful 
in  the  construction  of  a 
wooden  cow  for  Pasiphae 
(query,  was  this  the  original 
old  friend  of  the  modern 
milkman,  the  cow  with  the 
iron  tad — the  pump?),  and 
having  shut  up  the  dreadful 
monster,  the  Minotaur  (most 
likely  a  hippopotamus),  in  a 
labyrinth  at  Cnossus,  for  this 
stroke  of  benevolence  he  was 
imprisoned  by  Minos,  but 
his  old  friend  the  milk¬ 
woman  (at  least,  Pasiphae) 
released  him  ;  but  the  artful 
Minos  had  seized  all  the 
ships  on  the  coast  of  Crete, 
whereupon  Daedalus  '  pro¬ 
cured  wings  for  himself  and 
son,  and  fastened  them  on 
with  wax.  Strange  to  say, 
the  classical  authorities  re¬ 
late  that  they  Jlew  safely 
over  the  /Egean,  alighting  in 
Italy.  This “  ower-true  tale” 
has  brought  unhappiness  to 
the  bosoms  of  many  clever 
mechanicians,  who,  trying  to 
imitate  Daedalus,  have  only 
met  with  the  derision  of  their 
fellow-men  and  pecuniary 
loss  to  themselves. 

The  idea  which  the  inventor,  St.  Martins,  endeavoured  to  realize  is  that  of 
a  self-supporting  kite,  the  string,  the  restraining  power,  being  represented  by 
the  two  screw's.  The  inventor  maintains  that  his  flying  machine,  being  once 
fairly  launched,  the  force  of  the  wind  would  be  resolved  by  the  screws,  as  by 
the  string  of  the  kite,  into  two  powers,  one  of  which,  overcoming  the  force  of 
gravitation,  would  keep  it  stationary  in  mid-air. 

This  might,  by  the  barest  possibility,  be  achieved,  but  only  with  screws  so 
large  and  so  heavy,  and  requiring  such  powerful  and  weighty  machinery,  that 
the  whole  would  virtually  gravitate  to  mother  earth,  and  decline  to  fly  a 
single  inch  from  the  ground.  The  flying  machines  hitherto  suggested  are 
purely  visionary  ;  not  one  will  take  itself  up,  or  maintain  itself  in  the  air  like 
a  bird.  The  models  and  drawings  of  these  suggestions  are  undoubtedly 
pretty,  and  that  is  all  that  can  be  said  about  them  :  the  veritable  dying 
machine  is  yet  to  come. 


Fig.  421. — Davids  Standard  Aneroid 
Barometer. 


5°2 


PNEUMATICS. 


Mr.  Frederick  W.  Breary,  the  indefatigable  Secretary  of  the  Aeionautical 
Society,  has,  by  his  scientific  experiments  and  careful  digest  of  all  the  various 
modes  of  attempting  flight  in  the  air,  he'ped  greatly  to  increase  our  know¬ 
ledge  of  the  conditions  of  flight.  At  a  meeting  lately  held  at  the  Society  of 
Arts,  under  the  presidency  of  Mr.  Glashier,  F.R.S.,his  ‘‘ swallow-wing”  model 
was  particularly  admired,  darting  like  the  bird  from  the  hand,  and  rising 
swiftly,  as  if  to  its  nest,  near  the  ceiling.  The  writer  believes  that  a  motion 
similar  to  that  seen  in  the  various  Aquariums  of  the  Crystal  Palace,  South- 
port,  &c.,  and  performed  by  the  wave-like  motion  of  flat  fish  in  rising  or 
sinking  in  sea-water,  is  the  one  that  ought  to  be  studied  and  imitated  by 
makers  of  aeronautical  machines. 


Fig.  422. — One  of  the  Flying  Machines  (so  called)  exhibited  by  the  Aero¬ 
nautical  Society  at  the  Crystal  Palace ,  Sydenham. 

Having  connected  Galileo’s  name  with  the  philosophy  of  the  sucking-pump, 
we  may  now  describe  this  and  other  most  important  forms  of  pumps,  which 
have  been  found  so  useful  for  various  purposes. 

The  pump  was  first  invented  by  Ctesibius,  a  mathematician  of  Alexandria, 
120  years  before  the  Christian  era.  When  Galileo  defined  the  principle  upon 
which  the  common  pump  acts,  the  machine  was  soon  improved.  There  are 
three  kinds,  viz.,  the  sucking-pump,  the  forcing-pump,  and  lifting-pump.  (See 
Fig.  423.)  J 

The  construction  of  pumps  is  usually  explained  by  glass  models  in  which 
the  action  of  the  pistons  and  valves  may  be  seen.*  In  order  to  understand  the 
construction  and  operation  of  the  common  pump,  let  the  model  D  C  B  L  (1, 
Fig.  423)  be  placed  upright  in  the  vessel  of  water  K  K,  the  water  being  deep 
enough  to  rise  at  least  as  high  as  L.  The  valve  a  in  the  movable  bucket 
G,  and  the  valve  b  in  the  fixed  box  H  (which  box  fills  the  bore  of  the  pipe  or 


*  “  Rees’s  Cyclopaedia.” 


WATER-PUMPS, 


5°3 


barrel  at  H),  will  each  lie  close  by  its  own  weight  upon  the  hole  in  the  bucket 
and  box  until  the  engine  begins  to  work.  The  valves  are  made  of  brass,  and 
covered  underneath  with  leather,  for  closing  the  holes  more  exactly;  and  the 
bucket  G  is  raised  and  depressed  alternately  by  the  handle  E  and  rod  D  d,  the 
bucket  being  supposed  at  B  before  the  working  begins.  Take  hold  of  the 
handle  E,  and  thereby  draw  up  the  bucket  from  B  to  c,  which  will  make  room 
for  the  air  in  the  pump  all  the  way  below  the  bucket  to  dilate  itself,  by  which 
its  spring  is  weakened,  and  then  its  force  is  not  equivalent  to  the  weight  or 
pressure  of  the  outward  air  upon  the  water  in  the  vessel  K  ;  and  therefore  at 
the  first  stroke  the  outward  air  will  press  up  the  water  through  the  notched 
foot  A  into  the  lower  pipe  about  as  far  as  e;  this  will  condense  the  rarefied  air 
in  the  pipe  between  e  and  C  to  the  same  state  it  was  in  before  ;  and  then,  as  its 
spring  within  the  pipe  is  equal  to  the  force  or  pressure  of  the  outward  air,  the 
water  will  rise  no  higher  by  the  first  stroke;  and  the  valve  b ,  which  was  raised 
a  little  by  the  dilatation  of  the  air  in  the  pipe,  will  fall  and  stop  the  hole  in  the 
box  H,  and  the  surface  of  the  water  will  stand  at  e ;  then  depress  the  piston 
from  c  to  B,  and  as  the  air  in  the  part  B  cannot  get  back  through  the  valve  b , 
it  will,  as  the  bucket  descends,  raise  the  valve  a,  and  so  make  its  way  through 
the  upper  part  of  the  barrel  d  into  the  open  air.  But,  upon  raising  the  bucket 
G  a  second  time,  the  air  between  it  and  the  water  in  the  lower  pipe  at  c  will  be 
again  left  at  liberty  fo  fill  a  larger  space ;  and  so,  its  spring  being  again  weak¬ 
ened,  the  pressure  of  the  outward  air  on  the  water  in  the  vessel  K  will  force 
more  water  up  into  the  lower  pipe  from  e  to  f ;  and  when  the  bucket  is  at  its 
greatest  height  C,  the  lower  valve  b  will  fall  and  stop  the  hole  in  the  box  H  as 
before.  At  the  next  stroke  of  the  bucket  or  piston  the  water  will  rise  through 
the  box  H  towards  B,  and  then  the  valve  b,  which  was  raised  by  it,  will  fall 
when  the  bucket  G  is  at  its  greatest  height.  Upon  depressing  the  bucket 
again,  the  water  cannot  be  pushed  back  through  the  valve  b,  which  keeps 
close  upon  the  hole  whilst  the  piston  descends ;  and  upon  raising  the  piston 
again  the  outward  pressure  of  the  air  will  force  the  water  up  through  H,  when 
it  will  raise  the  valve  and  follow  the  bucket  to  C.  Upon  the  next  depression 
of  the  bucket  G,  it  will  go  down  into  the  water  in  the  barrel  B,  and  as  the  water 
cannot  now  be  driven  through  the  now  closed  valve  b ,  it  will  raise  the  valve  (i 
as  the  bucket  descends,  and  will  be  lifted  up  by  the  bucket  when  it  is  next 
raised ;  and  now,  the  whole  space  below  the  bucket  being  filled,  the  water 
above  it  cannot  sink  when  it  is  next  depressed,  but  upon  its  depression  the 
valve  ur  will  rise  to  let  the  bucket  go  down,  and  when  it  is  quite  down  the  valve 
will  fall  by  its  own  weight  and  stop  the  hole  in  the  bucket.  When  the  bucket 
is  next  raised,  all  the  water  above  it  will  be  lifted  up,  and  begin  to  run  ott  by 
the  pipe  F;  and  thus,  by  raising  and  depressing  the  bucket  alternately,  there 
is  still  more  water  raised  by  it,  which,  getting  above  the  pipe  I-  into  the  wu  i 
top  i,  will  supply  the  pipe  and  make  it  run  with  a  continued  stream.  So  at 
every  time  the  bucket  is  raised  the  valve  b  rises  and  the  valve  a  falls,  anc  at 
every'  time  the  bucket  is  depressed  the  valve  b  falls  and  a  rises.  As  it  is  t  te 
pressure  of  the  air  which  causes  the  water  to  rise  and  pull  the  piston  G  as  it 
is  drawn  up,  and  since  a  column  of  water  32  ft.  high  is  of  equal  weight  w  it  1  as 
thick  a  column  of  the  atmosphere  from  the  earth  to  the  top  ot  the  air,  t  ieri  - 
fore  the  perpendicular  height  of  the  piston  from  the  surface  of  the  water  in  t  c 
well  must  always  be  less  than  32  ft.,  otherwise  the  water  will  ne\  or  git  a  >(l'e 
the  bucket ;  but  when  the  height  is  less  the  pressure  of  the  atmosphere  w  ill 
greater  than  the  weight  of  the  water  in  the  pump,  and  will  therefore  raise  .. 


PNEUMATICS. 


5°4 


1  a  c  3 


Fig.  423.  —  Various  forms  of  Water-Pumps. 


above  the  backet ;  and  when  the  water  has  once  got  above  the  bucket  it  may 
be  lifted  by  it  to  any  height,  if  the  rod  D  be  made  long  enough,  and  a  sufficient 
degree  of  strength  be  employed  to  raise  it  with  the  weight  of  the  water  above 
the  bucket  without  even  lengthening  the  stroke.  The  force  required  to  work 
a  pump  will  be  as  the  height  to  which  the  water  is  raised  and  as  the  square  of 
the  diameter  of  the  pump-bore  in  that  part  where  the  piston  works ;  so  that 
if  two  pumps  be  of  equal  height,  and  one  of  them  be  twice  as  wide  in  the  bore 
as  the  other,  the  wider  one  will  raise  four  times  as  much  water  as  the  narrower, 
and  will  therefore  require  four  times  as  much  strength  to  work  it. 

The  Forcing-Pump  raises  water  through  the  box  H  (2,  Fig.  423),  not  in  the 
same  manner  as  the  sucking-pump  does  when  the  plunger  or  piston  g  is  lifted 
up  by  the  rod  D  d ;  but  this  plunger  has  no  hole  through  it  to  let  the  water  in 
the  barrel  C,  when  it  is  depressed  to  B,  and  the  valve  b  (which  rose  by  the 
ascent  of  the  water  through  the  box  H  when  the  plunger^  was  drawn  up)  falls 
down  and  stops  the  hole  in  h  the  moment  at  which  the  plunger  is  raised  to  its 
greatest  height— therefore,  as  the  water  between  the  plunger  g  and  box  H  can 
neither  get  through  the  plunger  upon  its  descent  nor  back  again  into  the  lower 
part  of  the  pump  L  *?,  but  there  being  a  free  passage  by  the  cavity  around  H 
into  the  pipe  M  M,  which  opens  into  the  air-vessel  K  K  at  P,  the  water  is  forced 
through  the  pipe  M  M  by  the  descent  of  the  plunger,  and  driven  into  the  air- 
vessel;  and  in  running  through  the  pipe  at  P,  it  opens  the  valve  rt,  which 
shuts  the  moment  the  plunger  begins  to  be  raised,  because  the  action  of  the 
water  against  the  under-side  of  the  valve  Ceases.  The  water,  being  thus  forced 
into  the  air-vessel  K  K  by  repeated  strokes  of  the  plunger,  gets  above  the  lower 
end  of  the  pipe  G  H  I,  and  then  begins  to  condense  the  air  in  the  vessel  K  K ; 
for  as  the  pipe  G  H  is  fixed  air-tight  into  the  vessel  below  F,  and  the  air  has 


PUMPS. 


5°5 


no  way  to  get  out  of  the  vessel  but  through  the  mouth  of  the  pipe  at  I,  and 
cannot  get  out  when  the  mouth  I  is  covered  with  water,  and  is  more  and  more 
condensed  as  the  water  rises  upon  the  pipe:  the  air  then  begins  to  act  forcibly 
by  its  spring  against  the  surface  of  the  water  at  H,  and  this  action  drives  the 
water  up  through  the  pipe  I  H  G  F,  from  whence  it  spouts  in  a  jet  S  to  a  great 
height,  and  is  supplied  by  alternately  raising  and  depressing  the  plunger  g, 
which  constantly  forces  the  water  that  it  raises  through  the  valve  ft,  along  the 
pipe  M  M,  into  the  air-vessel  K  K.  The  higher  the  surface  of  the  water  is  raised 
in  the  air-vessel,  the  less  space  the  air  will  be  condensed  into,  and  therefore 
the  force  of  its  spring  will  be  so  much  the  stronger  upon  the  water,  and  will 
drive  it  with  greater  force  through  the  pipe  at  F;  and  as  the  spring  of  the  air 
continues  whilst  the  plunger  gr  is  rising,  the  stream  or  jet  S  will  be  uniform  as 
long  as  the  action  of  the  plunger  continues;  and  when  the  valve  b  opens  to  let 
the  water  follow  the  plunger  upwards,  the  valve  a  shuts  to  hinder  the  water 
which  is  forced  into  the  air-vessel  from  running  back  by  the  pipe  M  M  into  the 
barrel  of  the  pump. 

The  Lifting-Pump  differs  from  the  sucking-pump  only  in  the  disposition 
of  its  valves  and  the  form  of  its  piston-frame.  This  kind  of  pump  is  shown 
at  3,  Fig.  423.  A  is  a  barrel  fixed  in  a  frame,  I  K.  L  M,  which  is  immovable, 
with  its  lower  part  communicating  with  the  water.  G  E  Q  H  o  is  a  frame  with 
two  strong  iron  rods  movable  through  holes  in  the  upper  and  lower  parts  of 
the  pump  I  K  and  L  M.  In  the  bottom  of  this  frame  Q  H  is  fixed  an  inverted 
piston  B  n,  with  its  bucket  and  valve  upon  the  top  at  D.  Upon  the  top  of 
the  barrel  is  fitted  F  R,  either  fixed  to  the  barrel  or  movable  by  a  ball  and 
socket,  but  in  either  case  water  and  air-tight.  In  this  part  at  C  is  fixed  a 
valve  opening  upwards.  It  is  evident  that,  when  the  piston-frame  is  thrust 
down  into  the  water,  the  piston  D  descends,  and  the  water  below  will  rush  up 
through  the  valve  D  and  get  above  the  piston,  and  that  when  the  frame  is  lifted 
up  the  piston  will  force  the  water  through  the  valve  C  into  the  cistern  P,  there 
to  run  oft  by  the  spout. 

The  PLUNGER  Force-Pump,  used  so  extensively  for  draining  mines,  is  a 
most  important  part  of  the  expensive  machinery  required  in  Cornwall  and 
other  parts  of  the  world  where  minerals  are  dug  from  great  depths. 

This  pump  is  wholly  unaffected  by  the  pressure  of  the  air.  and  is  worked  by 
i  .e  force  of  the  steam  engine  which  is  expended  in  lifting  the  pump-rods  and 
solid  plunger.  The  latter  fits  the  barrel  of  the  cylinder  of  the  pump,  and  slides 
through  a  collar  of  leather,  so  that  it  works  air-tight,  like  the  piston  of  a  hy¬ 
draulic  press. 

As  the  plunger  rises,  a  valve  opens  inwards  and  admits  the  water;  the  next 
movement  causes  the  plunger  and  pump-rods  tc  descend,  and  these  represent 
a  great  weight  and  mechanical  power,  which,  shutting  the  lower  valve,  01  ce 
the  water  upwards  through  another  valve,  and  by  this  great  pressure  the  water 
is  pumped  to  a  considerable  height.  ... 

To  prevent  excessive  pressure  upon  the  parts  of  a  single  pump,  it  is  usua  . 
where  the  depth  of  the  mine  is  considerable,  to  have  a  series  of  plunging  force- 
pumps  called  “lifts,”  and  by  passing  the  water  from  one  cistern  to  another  it 

is  gradually  raised  to  the  top  of  the  mine-shaft. 

The  records  of  the  pumping  work  done  by  the  famous  Cornish  engines  arc 
very  remarkable,  and  have  already  been  spoken  of  in  the  article  on  t  n.  .  team 
Engine,  page  iqi.  _  .  .  , 

A  beautiful  illustration  of  the  pressure  of  the  air  is  shown  in  the  simp  e  ton 


5°6 


PNEUMATICS. 


trivance  called  the  Syphon.  This  consists  of  a  bent  pipe,  whose  “  legs,”  as  the 
two  portions  are  called,  may  be  of  equal  or  unequal  lengths.  If  the  former, 
the  syphon,  when  filled  with  water  and  placed  in  a  vessel  containing  the  same, 
must  be  tilted  in  order  to  get  a  difference  in  the  length  of  the  column  of  water; 


Fig.  425. —  The  Law  of  Marriotte. 

and  if  this  be  not  done,  the  syphon  whose  legs  are  equal  in  length  will  not  act. 
Hence  it  is  usual  to  have  one  leg  longer  than  the  other;  and  by  attaching  a 
cord  and  counterweight  the  syphon  may  be  gradually  lowered  into  the  vessel 
as  the  fluid  is  removed. 

In  order  to  make  a  syphon  act,  it  is  necessary  first  to  fill  both  legs  quite  fuk 
of  the  liquid,  and  then  the  shorter  leg  must  be  put  into  the  vessel  to  be 
emptied.  Immediately  upon  withdrawing  the  finger  from  the  longer  leg,  the 
liquid  will  flow. 


THE  SYPHON. 


5°7 


If  the  short  end  of  the  syphon  be  passed  through  a  cork,  fitting  air-tight 
into  a  bottle  quite  full  of  water,  the  syphon  will  not  act,  although  the  greatest 
force,  with  the  mouth  or  other  means,  may  be  employed  to  suck  the  water  into 
the  syphon.  This  experiment  shows  that  the  term  “  suction  ”  means  nothing, 
and  that  the  syphon  will  only  act  when  the  pressure  of  the  air  is  admitted  to 
the  inside  of  the  bottle  by  removing  the  cork.  In  this  experiment  the  bottle 
must  be  quite  full  of  water :  if  any  air  is  left  under  the  cork,  it  will  expand 
when  the  exhauster  is  applied,  and  drive  the  water  into  the  syphon-tube. 

A  syphon  higher  than  33  ft.  would  not  act,  because  the  pressure  of  the  air 
is  balanced  by  the  height  of  the  column  of  water;  so  also  with  mercury,  the 
latter  will  flow  through  a  syphon,  provided  the  utmost  height  does  not  exceed 
that  of  the  barometer  at  the  time  it  is  being  used. 

The  intermitting  or  reciprocating  springs  are  good  examples  of  natural  sy¬ 
phons  which  only  flow  when  there  is  sufficient  water  to  fill  the  longer  channel, 
vein,  or  leg,  that  passes  from  the  cavity  in  the  earth  or  rock  in  which  the 
water  collects. 

Air,  in  common  with  many  other  gases,  is  one  of  the  most  clastic  bodies 
in  nature.  Dr.  Miller  says  it  may  be  stated,  without  sensible  error,  that, 
within  the  limits  of  ordinary  experiment,  the  volume  of  an  aeriform  body  is 
inversely  as  the  pressure  to  which  it  is  exposed;  consequently,  by  doubling 
the  pressure  we  halve  the  volume,  by  trebling  it  we  reduce  it  to  one-third; 
but  the  elasticity  is  increased  directly  as  the  pressure-  by  doubling  the  pres¬ 
sure  we  double  the  elasticity.  These  facts  are  strikingly  illustrated  in  t lie 
following  experiment,  devised  by  Boyle,  and  more  accurately  performed  by 
Marriotte.  (Fig.  425.) 

Take  a  bent  tube  of  thick  glass  (that  called  barometer-tube  is  the  best)  of 
uniform  bore,  one  limb  or  leg  of  which  is  about  12  in.  long,  and  furnished 
with  a  stop-cock,  the  other  limb  being  6  ft.  in  length,  and  open  at  the  top. 
Four  a  little  mercury  into  the  bend  of  the  tube,  and  close  the  stop-cock. 

The  air  in  the  short  leg  is  now  of  the  same  elasticity  as  that  of  the  atmo¬ 
sphere  at  the  spot ;  and  the  air  at  the  surface  of  the  earth  is  under  the  pressure 
due  to  the  weight  of  its  own  superincumbent  mass.  I  lie  amount  of  this 
pressure  is  ascertained  by  observing  the  height  of  the  mercurial  column  in  the 
barometer  at  the  time.  Next,  pour  mercury  into  the  open  and  longer  limb  of 
the  bent  tube;  the  air  in  the  shorter  limb  will  slowly  diminish  in  bulk.  \  hen 
the  mercury  in  the  longer  limb  stands  above  the  level  of  that  in  the  shorter 
one,  at  a  height  exactly  equal  to  the  height  of  the  barometer  at  the  time,  say 
29-92  in.,  the  compressed  air  will  occupy  a  length  of  the  shorter  tube  exact  y 
equal  to  one-half  of  that  which  it  did  at  the  beginning  of  the  experiment, 

the  air  is  subject  to  a  pressure  exactly  double.  .  , 

On  adding  more  mercury,  till  the  length  of  the  column  in  the  long  tube 
above  the  level  of  that  in  'the  shorter  is  equal  to  twice  the  height  of  the 
barometric  column,  the  pressure  will  be  increased  threefold;  and  t  ic  air  wi 
now  occupy  only  one-third  of  its  original  bulk. 

It  is  difficult  to  find  a  law  without  an  exception;  and  the  researches  of 
Despretz,  followed  by  the  more  elaborate  experiments  of  \egnati  ,  s  ro\ 
that  the  law  called  Marriotte’s  is  a  limited  law,  and  does  not  apply  in  an 
cases 

For  the  permanent  gases,  oxygen,  hydrogen,  and  nitrogen,  and  also 1  for 
gases  which  are  only  liquefied  by  enormous  pressure,  the  law  is  man  ^ 
for  many  atmospheres;  but,  with  gases  easily  liquefied,  they  arc  °u 


5°8 


PNEUMATICS. 


take  a  smaller  bulk  than  the  calculated  volume  when  they  approach  the  point 
af  liquefaction.  The  following  are  some  of  Regnault’s  results,  and  they  show 
considerable  deviations  from  Marriotte’s  law  in  four  important  gases  under 
great  pressures : 


Fressnre  in 
Atmospheres. 

Air 

Nitrogen. 

Carbonic 

Anhydride. 

Hydrogen. 

r 

1 000000 

roooooo 

roooooo 

roooooo 

ro 

9916220 

9‘94359° 

9226200 

10-056070 

20 

19719880 

19788580 

167054OO 

20-268270 

The  elasticity  of  hydrogen,  therefore,  increases  even  more  rapidly  than  the 
pressure:  with  the  other  gases  the  elasticity  does  not  quite  keep  pace  with 
it.  It  would  seem,  from  these  experiments,  as  if  there  were  more  probability 
of  liquefying  oxygen  than  nitrogen,  and  both  these  than  hydiogen. 

The  elasticity  of  air  is  easily  demonstrated  by  placing  a  closed  flaccid  bladder 
under  the  receiver  of  an  air-pump :  when  the  air  is  removed  the  bladder  swells 
up,  and  will  burst  if  too  much  air  has  been  left  in  it.  On  readmitting  the  air, 
the  bladder  sinks  again  to  its  former  bulk. 

An  empty  flask,  inverted  in  a  glass  containing  some  coloured  water,  and 
placed,  like  the  bladder,  under  a  receiver,  which  is  gradually  exhausted,  shows 
the  expansion  of  the  air.  Directly  the  pressure  is  taken  off,  bubbles  escape  in 
large  quantities  from  the  mouth  of  the  flask;  and  if  the  pumping  be  continued 
until  no  more  escapes  through  the  water  from  the  flask,  it  is  almost  instantly 
filled  with  the  coloured  water  when  the  air  is  permitted  to  rush  ir.to  the  receiver 
that  encloses  it. 


Fig.  426. 

a,  Wire  Cage";  and  b,  Bottle 


Fig.  427. —  Square  Bottle  burst  by  the 
Elasticity  of  the  Air. 


It  is  in  this  way  a  bottle  may  be  burst  01  the  cork  violently  driven  out 
w  ien  placed  under  similar  circumstances. 


THE  AIR-PUMP. 


509 


The  bottle  is  usually  made  very  thin  and  square;  it  has  a  cap  cemented  upon 
it,  with  a  bit  of  oiled  silk,  which  acts  as  a  valve,  and  opens  outwards. 

When  the  bottle  with  its  wire  cage  is  placed  under  a  proper  receiver,  and 
a  vacuum  produced,  the  air  by  its  elasticity  escapes  from  the  interior,  because 
the  oiled  silk  valve  open:;  outwards ;  on  permitting  the  air  to  flow  into  the  re¬ 
ceiver  the  valve  closes,  and  as  the  pressure  is  now  1 5  lb.  on  every  square  inch, 
the  bottle  is  usually  crushed  with  the  superincumbent  pressure. 

Or  the  experiment  may  be  reversed,  by  making  the  valve  open  inside  the 
bottle;  then,  on  pumping  out  the  air  from  the  receiver  which  encases  it,  the 
elasticity  of  the  air  in  the  bottle  is  checked  by  the  valve  shutting;  and  when 
a  sufficient  vacuum  has  been  obtained,  the  thin  square  bottle  bursts. 

When  a  long  receiver  is  placed  over  a  glass 
bottle  containing  water,  and  closed  with  a 
tight-fitting  cork,  or,  better  still,  a  brass  cap, 
through  which  a  tube  passes,  a  miniature  foun¬ 
tain  is  obtained  when  the  elasticity  of  the  air 
becomes  sufficiently  great  to  drive  out  the 
water  from  the  bottle  through  the  jet. 

The  Piezometer,  as  made  by  Mr.  Ladd,  is  a 
most  useful  and  safe  apparatus  for  showing  the 
condensation  of  certain  gases  which  are  easily 
liquefied.  (Fig.  429.) 

A  very  stout  vessel  encloses  a  tube  contain¬ 
ing  the  gas  to  be  liquefied,  which  is  further  sur¬ 
rounded  by  water;  and  by  a  clever  arrange¬ 
ment  of  bends  in  the  tube,  it  is  cut  off  from 
contact  with  the  water  by  mercury,  provided, 
of  course,  the  gas  does  not  act  upon  it.  1  he 
strong  glass  vessel  is  provided  with  a  very  stout 
cap,  which  is  securely  fixed  and  cemented  to 
the  top,  and  this  carries  the  vessel  containing 
water,  which  is  gradually  pumped  into  the 
vessel;  in  this  way  the  pressure  is  so  equally 
apolied,  that  the  tube  enclosing  the  gas  is  not 
subjected  to  any  unequal  force,  and  by  con¬ 
ducting  the  experiment  steadily  there  is  no 
fear  of  breaking  the  outer  vessel,  in  which,  of  course,  a  proper  pressure-gauge 
is  inserted. 

The  resistance  of  the  air  and  its  materiality  are  well  shown  whenever  we 
try  to  run  with  an  extended  umbrella  in  our  hands ;  but  even  this  simple  truth 
is  nicely  illustrated  by  a  miniature  double  windmill,  which  is  placed  under  a 
receiver  provided  with  a  rod  passing  through  a  collar  of  leather  to  which  a 
hook  is  attached.  (Fig  430.) 

I  he  sliding  hook  enables  the  operator  to  set  the  fans  in  motion  first  in  air, 
when  the  fans  with  the  flat  sides  exposed  to  the  air  come  to  rest  before  the 
fans  which  cut  the  air  edgeways  like  a  knife. 

On  pumping  out  the  air  from  the  receiver  and  again  setting  the  fans  in  mo¬ 
tion,  they  come  to  rest  at  the  same  time,  because  there  is  no  longei  any  re¬ 
sistance  to  their  motion,  which  is  produced  by  one  spring,  and,  being  equ a  , 
they  both  come  to  rest  together. 

The  guinea  and  feather  glass  is  another  example  of  the  same  kind. 


Fig.  428. — Miniature  Foun¬ 
tain —  IV ater  forced  out  by 
the  Elasticity  of  the  A  ir. 


PNEUMATICS. 


io 


FlG.  429. —  The  Piezometer  made  by 
Mr.  Laitd. 


Some  feathers  and  gold  pieces  are 
placed  on  a  drop  which  is  fixed  air¬ 
tight  with  grease  on  the  top  of  a  very 
long  cylindrical  glass  placed  upon 
the  air-pump  plate.  It  is  usual  to 
have  three  drops.  The  first  time, 
when  the  receiver  is  full  of  air,  the 
gold  piece  reaches  the  air-pump 
plate  first,  and  is  followed  by  the 
leather,  because  the  air  resists  its 
downward  tendency,  and  the  weight 
or  gravitating  force  of  the  feather  is 
so  slight  and  spread  over  so  large  a 
surface.  When  the  air  is  all  pumped 
out  and  a  second  drop  allowed  to 
fall,  the  gold  and  feather  fall  to¬ 
gether,  and  even  the  skilled  and  ex¬ 
perienced  umpire  of  a  horse-race 
would  be  unable  to  detect  any  dif¬ 
ference  in  the  time  of  their  fall 
through  the  large  jar  and  their  arri¬ 
val  simultaneously  on  the  plate  of 
the  pump.  The  third  drop  would  of 
course  corroborate  the  second,  as  it 
sometimes  happens  that  the  rapid 
fall  of  the  gold  and  feather  acts  as 
a  surprise,  and  the  result  is  not  pro¬ 
perly  observed  the  first  time. 


Fig.  430. 

The  M ill  with  two  Fans. 


The  application  by  Mr.  Barker,  of  Paris,  of  the  pneumatic  lever  to  the  organ 
has  wondrously  reduced  the  labour  of  playing  the  instrument  and  effected 
quite  a  revolution  in  the  touch,  and  the  organ  can  now  be  played  upon  almost 
with  the  same  facility  as  the  piano. 

“  It  has  also  been  mentioned  *  that  the  compressed  air  in  the  wind-chest 


“The  Organ.’’  B>  E  J.  Hopkin. 


THE  AIR-PUMP. 


5” 


became  a  second  source  of  resistance  to  the  touch  of  the  performer:  this  latter 
fact  is  discernible  even  in  small  organs  of  which  the  sound-boards  are  palleted 
in  the  ordinary  way,  by  striking  a  chord  in  the  bass  part  of  the  manual  first, 
without  the  bellows  being  blown  ;  then  with  the  wind  in,  when  the  additional 
resistance  which  the  organ-wind  causes  will  be  at  once  perceived.  In  large 
organs  which  have  pallets  of  increased  size  throughout  the  sound-board,  with 
two  pallets  in  the  bass,  the  amount  of  spring  and  wind-resistance  is  of  course 
much  increased,  particularly  where  there  are  octave  and  double  couplers 
causing  six  or  seven  pallets  to  operate  in  one  key.  But  in  instruments  of  the 
first  magnitude,  containing  as  they  now  do  some  stops  on  a  heavy  pressure 
of  wind,  the  resistance  becomes  too  great  for  even  the  most  muscular  finger  to 
control  without  much  fatigue.  In  such  cases,  it  being  beyond  the  power  of 
the  several  devices  to  remove  the  disagreeable  stiffness  from  the  touch — or 
perhaps  none  of  them  may  be  adopted  —  some  contrivance  is  required  that 
shall  bodily  overpower  the  resistance.  The  pneumatic  lever  performs  this 
necessary  duty  most  efficiently,  and  in  doing  this  converts  the  organist’s  anta¬ 
gonist  into  his  assistant. 

“The  first  idea  of  a  pneumatic  lever  originated  with  Mr.  Booth,  organ- 
builder,  of  Wakefield;  but  his  appliance,  made  in  1823,  was  not  intended  for 
key  movements.  The  merit  of  discovering  the  pneumatic  lever  as  a  means 
for  lightening  the  touch  of  large  instruments  is  claimed  by  and  rests  between 
Mr.  David  Hamilton,  of  Edinburgh,  and  Mr.  Barker,  late  of  Bath,  but  now  a 
resident  of  Paris.  Mr.  Hamilton  added  a  movement  of  the  kind  to  the  organ 
of  St.  John’s  Episcopal  Church  in  that  city  in  1835.  At  what  earlier  period 
he  had  completed  his  model  is  not  stated;  but  in  1839  a  paper  was  read  at 
the  meeting  of  the  British  Association  at  Birmingham  explanatory  ot  a  pneu¬ 
matic  lever  which  he  then  exhibited. 

“  Mr.  Barker’s  first  attempts  were  made  with  a  cylinder  and  piston,  which 
were  afterwards  abandoned  in  favour  of  small  bellows.  In  the  first  instance 
he  endeavoured  to  introduce  his  apparatus  into  England  about  1832;  experi¬ 
ence,  however,  in  large  organs  was  then  wanting  in  this  country,  and  his  en¬ 
deavours  were  unsuccessful.  He  therefore  went  to  France,  where  the  subject 
was  better  known,  and  the  value  of  the  new  principle  was  appreciated.  It  was 
introduced  in  the  great  organ  of  St.  Denis  (1841),  and  has  since  been  applied 
to  a  number  of  large  instruments  in  the  principal  churches  of  France,  as,  for 
instance,  the  Madeleine  and  St.  Vincent  de  Paul,  &c. 

“The  pneumatic  lever,  as  made  by  different  organ-builders,  varies  slightly 
in  detail,  but  the  following  is  the  principle  in  all: 

“  The  upper  member  of  the  lever  is  formed  very  like  a  small  concussion- 
valve.  (Sec  A,  Fig.  431.)  The  former  shows  the  lever  closed,  the  other  open. 
Beneath  the  lever  are  two  little  chambers,  c  c  and  d  d,  between  which  passes 
a  third,  e  e  e\  below,  again,  is  a  kind  of  back-fall,  o  o,  which  controls  two  cir¬ 
cular  pallets,  b  b,  in  such  a  manner  that  when  one  is  open  the  other  is  closed. 
Lastly,  to  the  rising  end  of  the  lever  a  small  lug  is  attached,  which  draws  up 
a  tracker  that  sets  the  several  key  movements  in  motion.  Lpon  pressing 
down  a  key  on  any  of  the  manuals,  the  movement  draws  down  the  near  enc 
cf  the  back-fall  0  o,  causing  the  far  end  to  rise,  which  motion  places  the  cir¬ 
cular  pallets  b  b  in  the  position  shown  in  the  figure.  Some  ot  the  'vnui  loan 
the  chamber  c  c  now  passes  downwards  through  the  uncovered  pallet-hole, 
traverses  the  passage  e  e  e,  raising  and  filling  the  pneumatic  lever,/!,  'Hm  1 
draws  up  the  tracker,  communicating  the  impulse  to  all  the  sound-boan 


512 


PNEUMATICS. 


pallets  that  may  be  attached  to  the  controlling  key ;  the  circular  pallet  in  the 
second  chamber,  d  d,  at  the  same  time  closes,  and  prevents  any  escape  of 
wind.  When  the  finger  is  withdrawn  from  the  key,  the  position  of  the  back¬ 
fall,  and  consequently  of  the  circular  pallets,  is  reversed,  as  shown  in  the  figure. 
The  supply  of  air  from  the  wind-chamber  is  now  cut  off  by  the  descent  of  the 
pallet ;  at  the  same  time  the  second  pallet  in  the  chamber  d  d  is  raised,  allow¬ 
ing  the  wind  to  descend  through  the  pallet-hole,  and  to  escape  through  the  open¬ 
ing  z  into  the  atmosphere.  The  contents  of  the  lever  being  thus  exhausted, 
it  returns  to  its  state  of  rest,  as  shown  at  B,  Fig.  431,  the  rapidity  of  the  change 
being  accelerated  by  a  spring. 


“In  consequence  of  the  width  of  the  pneumatic  lever — about  3  in.  only — 
every  fifth  lever  is  placed  in  the  same  row;  hence  the  pneumatic  action  always 
appears  in  five  rows,  as  shown  in  the  general  section.  The  pneumatic  action 
which  effects  such  remarkable  results  as  those  already  detailed  is  not  entirely 
unattended  with  disadvantage :  in  many  of  the  specimens  made  by  the  best 
builders,  English  and  Continental,  the  working  of  the  levers  is  as  audible  as  the 
motion  of  the  old  rattling  key  movements  of  old  organs.  This  arises  partly 
from  the  nature  of  the  action  itself,  which  to  be  effectual  must  also  be  very 
energetic.  Nevertheless,  the  defect  alluded  to  will,  no  doubt,  be  speedily 
ameliorated,  if  not  entirely  removed,  under  the  exercise  of  the  ingenuity  pos¬ 
sessed  by  so  many  English  builders.”  I 

Nearly  all  the  experiments  which  have  been  explained  serve  to  prove  the 
mechanical  power  of  the  atmosphere ;  and  the  question  how  it  could  be  con¬ 
verted  into  a  motive  power  available  for  the  conveniences  of  society  has  been 


THE  PNEUMATIC  LEVER. 


5  >3 


a  problem  of  great  interest  to  engineers.  Even  two  centuries  ago  the  notion 
was  entertained  of  producing  motion  economically,  for  the  purpose  of  transit, 
by  means  of  the  pressure  of  the  atmosphere.  The  original  thought  may  at 
least  be  traced  back  with  certainty  to  the  celebrated  Dr.  Papin;  in  succession 
long  afterwards  came  Lewis,  Vallance,  Medhurst,  and  Pinkus,  whose  specu¬ 
lations  excited  in  their  day  some  attention.  Towards  the  close  of  the  last 
century'  Murdoch  was  devoting  his  attention  to  this  subject.  The  means  of 
propulsion  he  proposed  to  employ  was  watery  vapour  working  an  air-pump; 
his  plan,  however,  consisted  simply  of  an  exhausted  tube,  through  which  might 
be  propelled  a  hollow  sphere  containing  letters  and  packages.  In  the  year  1810 
a  proposal  was  made  by  Medhurst,  the  Danish  engineer,  to  put  letters  and 
goods  in  a  canal.  6  ft.  high  and  5  ft.  wide,  and  containing  a  road  of  stone  and 
iron,  and  project  them  by  means  of  atmospheric  rarefaction  and  condensation. 
In  1 824  an  Englishman — Mr.  Vallance — made  a  similar  suggestion.  Hisdaring 
plan  was  to  connect  Brighton  and  London  by  means  of  an  enormous  tube, 
through  which,  by  pumping  out  the  air,  carriages  were  to  be  propelled  with 
the  velocity  of  a  cannon-bail.  Another  proposal  was  made  by  Medhurst:  he 
speedily  devised  means  of  propelling  his  carriage  in  the  open  air,  and  of 
making  a  communication  between  the  interior  of  his  propulsion-tube  and  the 
outside,  preserving  it  at  the  same  time  air-tight.  The  opening  was  to  be  closed 
by  a  hydraulic  apparatus  called  a  water-valve. 

Beautiful  as  Med  hurst’s  scheme  was  in  theory,  it  was  at  that  time  imprac¬ 
ticable,  and  his  experiments  were  unsuccessful :  the  water-valve  refused  to  ex¬ 
clude  the  air  from  the  tube.  In  this  state  was  the  contrivance  when  taken  up 
by  Mr.  Pinkus,  who  sugges.ed  the  rope-valve,  which  likewise  failed  to  keep 
the  tube  air-tight,  and  was  in  turn  abandoned. 

Another  inventor  came  forward  in  the  person  of  Murdoch’s  pupil  in  the 
Soho  factory' — Samuel  Clegg.  The  v  lve  invented  by  him,  in  conjunction  with 
Mr.  Jacob  Samuda,  of  the  Southwark  Ironworks,  gave  the  final  touch  to  Med- 
hurst’s  proposal,  and  led  to  the  construction  of  the  Kingston  and  Dalkey,  the 
Croydon,  and  several  other  atmospheric  lines.  These  lines  at  last  yielded  to 
the  locomotive,  and  ceased  to  exist. 

Murdoch  and  Vallance  proposed  the  use  of  a  pneumatic  tube  for  the  trans¬ 
mission  of  parcels.  With  them  the  motive  power  and  parcel-carriage  were 
both  to  be  in  a  tube.  It  is  the  same  with  regard  to  the  arrangement  of  the 
Pneumatic  Despatch  Tube  of  the  present  day.  Medhurst  and  Vallance  pro¬ 
posed  to  use  a  pump;  but  the  Despatch  Company  now  attain  the  same  object 
with  an  artificial  blast,  or  wind  produced  by  means  of  a  revolving  fan. 

Mr.  Latimer  Clark  used  pneumatic  tubes  for  several  y  ears  as  a  means  ot 
intercommunication  between  the  Electric  Telegraph  Company  s  offices  at 
Lothburv  and  their  branch  stations  at  Cornhill,  the  greatest  length  ol  the  tube 
being  three-quarters  of  a  mile.  Any  one  wishing  to  send  a  message  by  tele¬ 
graph — say  to  Edinburgh  from  Cornhill — the  message  is  written  down  on  a 
piece  of  paper,  rolled  up  in  a  small  gutta  percha  box,  and  placed  in  the  time , 
by  the  pressure  of  the  atmosphere  it  is  quickly  blown  through  the  tube,  just 
like  a  pea  out  of  a  pea-shooter,  and  falls  out  of  the  end  of  the  pipe  at  Lot  1- 
bury;  the  box  is  opened,  and  the  paper  with  the  message  written  upon  it  is 
handed  over  to  the  operator  at  the  telegraph  instrument  in  connection  witi 
Edinburgh,  and  the  message  is  instantly  sent.  .  . 

The  Pneumatic  Parcel  Despatch  tube,  delineated  at  the  head  of  this  article, 
p.  433,  Fig.  401,  is  now  working  most  successfully  between  the  arrival  p  at  01  n. 

33 


5*4 


PNEUMATICS. 


of  the  Euston  Square  Station  and  the  North-Western  District  Post  Office  in 
Eversholt  Street ;  and  it  is  better,  for  the  sake  ot  simplicity,  first  to  explain  the 
arrangements  which  are  made  for  the  purpose  of  sending  carriages  containing 
letters  to  and  fro. 

On  entering  the  building  erected  for  the  necessary  machinery  at  Euston 
Square,  the  engineer  in  charge  points  out  the  pneumatic  tube,  which  is  very 
much  like  an  elliptical  gas-main,  33  in.  by  30  in.  wide,  and  laid  at  an  average 
depth  of  about  9  ft.  below  the  road. 

The  pipes  are  made  in  9  ft.  lengths,  with  socket  joints  filled  in  with  lead  to 
keep  them  quite  air-tight,  and  on  the  inside — at  the  bottom  of  the  tube — are 
cast-iron  rails  2  ft.  apart.  The  car  to  run  on  these  weighs  nearly  8  cwt.,  and 
is  about  8  ft.  long,  and  runs  upon  four  wheels  20  in.  in  diameter.  We  have 
thus,  in  a  very  few  words,  described  almost  the  plant  and  rolling  stock  of  a 
Pneumatic  Despatch  Railway.  The  car,  when  placed  in  the  tube  on  the  rails, 
is  blown  from  end  to  end,  backwards  and  forwards,  as  may  be  required.  As 
we  have  already  seen,  air  has  weight,  and  this  brings  it  under  the  influence 
of  the  laws  of  centrifugal  force,  which  give  it  a  tendency  to  fly  off  with  more 
or  less  pressure,  according  to  the  velocity  with  which  it  is  whirled  round  from 
a  centre.  It  is  this  well-known  law  which  is  taken  advantage  of  in  working 
the  pneumatic  tube.  At  the  side  of  the  tube  in  the  small  building  at  Euston 
Station  is  a  hollow  iron  wheel  working  in  an  air-tight  box.  This  wheel  is  21  ft. 
in  diameter,  with  a  thickness  of  about  2  ft.  at  the  nave  or  centre — a  thickness 
which  gradually  diminishes  towards  its  outer  circumference,  so  as  to  give  it 
the  same  cubical  contents  at  the  rim  as  at  the  middle.  This  wheel  is  connected 
with  a  steam-engine  of  about  17-horse  power,  which  turns  it  at  a  velocity  of 
from  seventy  to  ninety  miles  an  hour,  when  the  air  which  is  drawn  in  through 
the  centre  is  thrown  off  from  its  periphery  with  a  force  which  gives  a  pressure 
of  from  5  to  7  oz.  on  the  square  inch, — very  nearly  the  pressure  of  a  hurri¬ 
cane,  and  all  of  which,  by  opening  a  valve  at  the  end  of  the  tube,  is  driven 
through  it  with  almost  irresistible  velocity.  The  cars  when  on  the  rails  inside 
the  tube  almost  fill  it,  and  expose  a  surface  of  nearly  5  ft.  square  to  the  blast. 
They  are  driven  along  at  the  rate  of  nearly  thirty  miles  an  hour. 

The  whole  apparatus  is  of  the  most  simple,  cheap,  and  effective  character, 
and  reflects  great  credit  upon  its  engineer,  Mr.  Ramrnel,  for  the  ease  and  cer¬ 
tainty  with  which  the  air  from  the  wheel  sends  one  or  more  carriages,  heavily 
laden,  from  one  end  to  the  other.  For  demonstration  at  the  Polytechnic,  a 
little  model  of  wood  was  constructed  about  20  ft.  long.  There  were  two 
carriages ;  the  passengers  consisted  of  a  party  of  white  mice,  and  they  were 
blown  from  one  end  of  the  tube  to  the  other  by  means  of  the  blast  of  air  from 
a  fan-blower  which  was  set  in  motion. 

The  company  proposed  to  lay  down  a  line  of  48-in.  tubes  to  form  pneumatic 
stations  in  connection  with  the  Camden  Town  Station  of  the  London  and 
North-Western  Railway  —  a  central  site  in  Holborn  —  the  Smithfield  new 
market ;  in  Gresham  Street,  in  connection  with  the  large  carrying  firms  for 
goods  and  parcels;  the  General  Post  Office;  Covent  Garden  Market;  and 
the  new  terminus  of  the  South-Eastern  Railway  at  Charir.g  Cross.  It  is 
stated  that  Messrs.  Pickford  alone  convey  400  tons  of  parcels  a  day  through 
London,  at  a  cost  of  ninepence  per  ton;  whereas  the  Pneumatic  Company 
could  do  the  same  work  quicker  at  a  penny  a  ton  a  mile,  and  yet  gain  largely 
by  the  undertaking.  Between  the  Pneumatic  Despatch  and  the  Underground 
Railway,  which  should  amalgamate,  the  days  ought  to  be  fast  approaching 


THE  PNEUMATIC  LEVER. 


when  the  ponderous  goods  vans  that  now  fly  between  station  and  station 
shall  disappear  for  ever  from  the  streets  of  London.  If  this  could  be  brought 
about  by  the  Pneumatic  Despatch  Tube,  it  would  be  of  great  service  to  the 

public. 

In  a  brilliant  leader  of  the  9th  November,  1865,  “  The  Times  ”  thus  speaks 
of  the  pneumatic  principle,  which,  unhappily,  in  these  depressed  engineering 
times  seems  to  be  in  abeyance : 

“  Every  dog  has  its  day,  and  even  the  elements  have  their  turns.  Earth, 
air,  fire,  and  water  contend  which  shall  render  the  greatest  service  to  man, 
and  enjoy  the  foremost  place  in  the  continual  triumph  of  nature  and  art.  In 
the  single  matter  of  locomotion,  earth  first  was  everything,  and  man  trudged, 
rode,  or  drove.  Then  water  had  its  turn,  and  man  paddled,  rowed,  sculled, 
drifted,  or,  with  earth’s  aid,  punted  or  was  pulled.  Then  air  lent  a  wing,  and 
the  sail  carried  him  across  gulfs  and  oceans.  Then  fire,  or  rather  steam,  the 
child  of  fire  and  water,  enabled  him  to  beat  the  winds  and  currents,  first  on 
water,  then  on  land.  At  this  time  we  can  hardly  see  by  what  infatuation  we 
land  lubbers  allowed  the  stormy  ocean  to  take  the  lead  of  terra  firnm  in  the 
use  of  steam  for  locomotion.  We  were  actually  laughing  at  the  prejudices  of 
old  skippers  when  we  had  not  a  thought  of  steaming  by  land.  But  now  comes 
a  new  move,  whereof  no  man  can  see  the  end,  though  it  begins  timidly  and 
awkwardly.  Air  is  now  the  performer.  It  comes  upon  the  scene  with  much 
modesty,  as  if  knowing  itself  to  be  suspected  of  wildness,  treachery,  and  ca¬ 
price.  It  only  asks  to  operate  in  strong  iron  tubes,  and  tunnels  of  masonry 
in  the  solid  ground.  Like  the  ass  of  Scripture,  which  is  not  as  our  degenerate 
specimens,  it  wants  the  bridle,  not  the  whip.  We  have  only  to  raise  the  wind, 
a  process  easier  in  these  days  than  when  Lord  Bacon  put  ‘  impressions  of  the 
air  and  raising  of  tempests’  among  the  magnalia  naturcc.  I  he  wind  once 
raised,  it  will  go  as  we  direct  it,  but  still  a  prisoner,  and  only  revolving  to  and 
fro  in  its  subterraneous  labyrinth.  The  notion  is  so  simple  that  when  the 
thing  is  once  done  everybody  will  ask  why  it  was  not  done  before.  Boys  will 
break  windows,  and  savages  before  this  have  pierced  the  tough  skin,  with  pea¬ 
shooters.  Indeed,  everybody  knows  the  power  of  wind  under  due  control. 
Everybody  has  seen  the  ‘lorry’  with  half-a-dozen  men  or  more  hurrying  on 
under  no  other  propulsion;  and  woe  to  a  full-sized  railway  carriage  if  it  be 
caught  by  a  too  favourable  gale.  But  it  is  quite  plain  that  the  friction  of  an 
ordinary  carriage  on  rails  cannot  be  a  greater  obstacle  than  the  resistance  of 
the  water  to  a  laden  ship,  which  nevertheless  is  soon  ovevcome  by  even  a 
moderate  breeze.  So  this  is  nothing  more  than  land  sailing,  with  two  simple 
differences  as  compared  with  sea  and  liver  sailing.  I  he  track  and  the  'vind 
must  be  fixed  and  in  accord.  In  fact,  the  ship  must  be  blown  through  a  tube. 


Fig.  432. — The  Talking  Head  of  Albertus  Magnus . 


ACOUSTICS. 


HP  HE  science  which  treats  of  the  nature  and  laws  of  sound  has  received  con- 
Jl  siderable  attention  from  learned  men.  500  B.C.,  Pythagoias  determined 
that  notes  of  music  varied  precisely  in  the  ratio  of  the  length  of  the  strings 
used.  Two  hundred  years  after  his  time,  Aristotle  wrote  upon  sound,  and 
affirmed  that  the  number  of  vibrations  performed  by  strings  or  by  the  air  in 
pipes  is  inversely  as  their  lengths ;  and  that  sound  is  transmitted  to  the  ear 
by  similar  vibrations  communicated  to  the  atmosphere.  Sixteen  hundred 
years  after  Christ.  Galileo  rediscovered  what  had  been  known  to  the  ancients, 


MARL  O  YE 'S  INTR OD  UCTION 


5*7 


and  taught  that  sound  is  a  vibration  of  the  air,  and  that  musical  sounds  differ 
only  in  the  frequency  of  the  vibrations  wh;ch  produce  them,  whilst  a  musical 
string  preserves  its  uniformity  of  tone  by  performing  its  vibrations  in  equal 

times. 

Passing  at  once  to  the  beginning  of  the  present  century,  we  find  Dr.  Thom  as 
Young  reviving  the  undulatory  theory  of  light,  and  at  the  same  time  enriching 
the  science  of  acoustics  with  much  original  matter.  The  names  of  Chladni, 
Savart,  Wheatstone,  and  Tyndall  bring  us  to  the  present  period.  Amongst 
the  French  philosophers  who  have  laboured  industriously  in  the  science  of 
acoustics  none  are  mere  distinguished  than  M.  Marloye,  whose  introduction 
to  a  catalogue  of  the  principal  apparatus  for  demonstrating  the  science  of 
acoustics,  made  by  Charles  Chevallier,  enunciates  some  very  original  views, 
and  is  therefore  translated  as  follows : 

Marloye’s  Introduction  to  Chevallier s  Catalogue. 

Fifteen  years  ago  Marloye  said,  of  all  the  branches  of  physics,  that  of 
acoustics  is  certainly  the  least  advanced.  Perhaps  for  this  reason  it  now 
attracts  the  most  attention  in  Europe,  as  offering  the  widest  field  for  investiga¬ 
tion.  And  yet  the  progress  of  this  science  is  so  slow  that  each  professor  of 
physics  might  individually  imagine  he  was  the  only  person  occupied  in  its 
cultivation.  Now,  if  this  science  advances  but  little,  notwithstanding  the  un¬ 
ceasing  efforts  of  a  great  number  of  talented  men,  it  is  evidently  because  we 
have  arrived  at  a  point  at  which  means  of  observation  are  wanting  to  penetrate 
further  into  the  secrets  of  Nature. 

Up  to  the  present  time,  strange  to  say,  we  have  used  our  eyes  more  than  our 
ears  in  the  study  of  acoustics,  and,  when  we  have  not  been  able  to  employ 
them,  they  have  been  supplied  by  calculation  and  by  imagination.  Thus, 
thanks  to  ingenious  devices  for  making  the  vibratory  motions  of  solid  bodies 
sensible  to  the  eye,  we  have  acquired  much  information  concerning  the  vibra¬ 
tions  of  strings,  plates,  rods,  &c.;  but  what  do  we  know  of  the  vibrations  of 


FIG.  433. — Chladni's  Sand  Figures. 


liquids  and  of  gases?  We  are  aware  of  many  formulas,  based  on  conjectures 
more  or  less  probable,  but  know  little  or  nothing  of  absolute  facts,  since  we 
still  make  researches  to  ascertain  how  the  air  vibrates  in  the  tubes  of  an  organ. 
The  reason  is  this:  the  vibrations  of  liquids  and,  above  all,  of  gases,  having 
been  hitherto  inaccessible  to  the  eye,  there  remained,  to  follow  the  thread  of 
so  many  different  motions,  no  other  guide  but  the  ear,  which,  from  not  having 
received  an  education  adanted  to  this  kind  of  study,  has  been  frequently  use- 


ACOUSTICS. 


518 


less  under  circumstances  where  its  aid  was  indispensable,  and  even  when  it 
heard  all  that  we  desired  to  ascertain. 

It  appears,  however,  that  the  necessity  of  an  ear  instructed  for  the  study  of 
acoustics  has  been  felt  at  all  times ;  for  we  still  find  professors  of  acoustics  ! 
more  or  less  musicians,  and  at  the  present  day,  when  a  person  acquainted  with 
general  physics  wishes  to  devote  himself  to  the  study  of  this  science,  he  com¬ 
mences  by  learning  music,  if  he  be  not  already  acquainted  with  it.  He  cer- 
tainly  ought  to  know  something  of  music;  but  it  is  an  error  to  suppose  that 
one  must  be,  or  that  it  suffices  to  be,  a  musician  to  form  an  accurate  judgment 
of  sounds  in  general :  we  may  even  say  that  musicians  are  bad  appreciators 
of  sounds  not  used  in  music— and  they  are  assuredly  the  more  numerous; 
sometimes  they  even  judge  wrongly  of  musical  notes  when  the  relations  of  ; 
these  notes  to  each  other  do  not  approach  to  musical  precision,  from  a  habit 
they  have  acquired  of  not  listening  to  sounds  which  are  grating  to  the  ear. 

When  a  musician  hears  sounds,  what  strikes  him  is  the  notes  they  represent, 
and  their  exact  mutual  relation,  not  so  much  from  their  musical  interval  as  , 
from  their  relation  of  note  to  note,  and  what  he  listens  to  is  their  tone  and 
intensity;  from  whence  it  results  that,  the  moment  the  sounds  he  hears  no 
longer  produce  on  him  the  impression  of  notes,  he  hears  only  noise,  and  can 
no  longer  judge  of  anything. 

For  the  professor  of  physics,  whose  task  is  to  appreciate  sounds  as  a  result 
of  vibrations  however  produced,  the  case  is  quite  different.  Here  there  is  no 
musical  preoccupation.  When  we  listen  to  a  sound  to  learn  something— and 
this  is  invariably  our  object— we  may  pay  but  little  attention  to  its  distinctness, 
since  this  is  known  from  the  first :  what  must  be  carefully  listened  to  are  the  : 
feeble  sounds  which  always  precede  it,  those  which  accompany  it,  and  those 
which  sometimes  follow  it.  If  we  listen  to  the  tone  of  a  sound,  we  should  only 
keep  in  view  the  detection  of  the  mode  of  vibration,  or  the  different  sounds 
which  may  produce  it.  Finally,  if  we  listen  to  two  or  to  several  sounds  at  the 
same  time,  it  should  merely  be  to  appreciate  their  musical  interval,  or,  to  speak 
more  strictly,  their  numerical  relation ;  but  as  we  can  have  an  idea  of  their 
numerical  relation  only  from  their  musical  interval,  it  follows  that  the  professor 
of  physics  is  obliged  to  be  cognizant  of  these  intervals:  this  is  the  only  musical 
knowledge  he  requires  for  all  that  concerns  the  appreciation  of  sounds;  but 
of  this  he  ought  to  be  master,  for  if  he  have  doubts  respecting  a  single  interval, 
he  may  deceive  himself  just  as  easily  by  an  interval  of  ten  notes  as  by  one  of 
a  half-note. 

Think  of  what  immense  resources  the  ear  would  procure  us  if,  instead  of 
often  hearing  noises,  it  always  heard  sounds;  if,  ever  aware  of  what  it  hears, 
it  could  distinguish  and  separate  many  sounds  where  we  imagine  we  hear  but 
one;  if  it  could  appreciate  the  numerical  relations  existing  between  them;  if 
it  could  recognize,  by  the  intensity,  the  tone,  and  certain  relations,  what  kinds 
of  vibrations  might  produce  them,  what  rank  they  hold  in  the  harmonic 
scale — if  they  arise  from  a  regular  and  easy  division  of  matter,  or  from  an 
irregular  and  constrained  division ;  and,  finally,  whether  they  arise  from  the 
coincidence  of  two  or  of  several  sounds.  Certainly  we  should  then  have  reason 
to  hope  that  the  assistance  of  the  ear  in  well-directed  researches  would  not  be 
of  less  importance  in  investigating  the  vibrations  of  liquids  and  of  gases  than 
the  aid  of  the  eye  has  hitherto  been  in  the  investigation  of  the  vibrations  of 
solid  bodies. 

But  is  it  possible  that  education  can  render  the  ear  fitted  for  such  functions  ? 


THE  EAR. 


5X9 


Ah  !  what  may  we  not  expect  from  this  precious  organ,  whose  least  merit  is 
to  keep  watch  almost  constantly,  to  bring  under  our  observation  and  instruct 
us,  without  ceasing,  concerning  things  that  interest  us,  even  when  we  do  not 
think  of  listening  to  them  ! 


Fig.  434. — Drawing  made  from  the  Microscope ,  by  Mr.  Lewis  A  Idons,  of  the 
Tympanum  ( or  Drum )  of  the  Ear , 

Showing  its  remarkable  organization,  and  the  number  of  blood-vessels  which  are  spread  over  its  whole 
surface.  The  smaller  figures.  Ban  I  c,  represent  the  inside  and  side  view  of  the  drum,  showing  the  small 
hones  of  the  ear,  viz.,  the  malleus,  or  hammer  ;  the  incus,  or  anvil ;  the  stapes,  or  stirrup ;  the  last  two 
bones  being  connected  with  a  small  round  hone,  called  the  os  ot  buulare. 


Is  its  memory  defective?  Does  not  the  peasant  recognize  the  sound  of  his 
village  bell  thirty  years  after  he  has  left  it?  Do  not  we  recognize  a  person 
whom  we  have  not  seen  for  twenty-five  or  thirty  years,  and  when  the  ravages 
of  time  have  altered  his  personal  appearance,  by  the  sound  of  a  single  word 
that  he  pronounces?  Has  not  the  musician  ever  the  sound  of  his  tuning-fork 
diapason  in  his  ear,  notwithstanding  the  multitude  of  sounds  which  he  hears 
incessantly,  and  which  apparently  ought  to  make  him  forget  it  ? 

Is  its  sensibility  defective?  If  there  be  question  of  the  sensibility  which 
consists  in  appreciating  feeble  sounds,  does  it  not  hear  the  sound  produced  in 
the  air  by  the  wings  of  a  fly  with  a  degree  of  certainty  sufficient  to  determine 
exactly  the  number  of  strokes  of  the  wings  made  by  the  fly  in  each  second  of 
time?  If  there  be  que  tion,  on  the  contrary,  of  the  sensibility  whose  limits 
are  contained  between  the  highest  and  lowest  notes,  here  the  latitude  o*  the 


520 


ACOUSTICS. 


eaf  is  immense,  since  it  appreciates  with  certainty  all  the  sounds  comprised 
between  thirty-two  vibrations  in  a  second  and  ten  thousand ;  and  it  may  go 
far  beyond  this,  as  I  proved  by  tuning,  for  M.  Despretz,  eight  tuning-forks, 
forming  an  octave  of  notes,  between  sixteen  thousand  and  thirty-two  thousand 
vibrations  in  a  second,  or  about  two  octaves  beyond  the  limits  of  musical 
notes;  and  if  I  failed  in  tuning  the  octave  which  followed,  it  was  doubtlessly 
from  want  of  skill,  for,  although  1  failed  in  producing  the  intermediate  notes, 

I  succeeded  in  the  octave  of  the  last  note,  which  corresponded  to  sixty-four 
thousand  vibrations  in  a  second.* 

Is  it  less  adapted  to  separate  and  appreciate  the  different  sounds  which  1 
concur  for  the  production  of  any  of  its  sensations  ?  Assuredly  not.  When  : 
the  leader  of  an  orchestra  hears  a  chord  which  is  frequently  formed  by  the  ; 
concurrence  of  all  the  instruments  placed  under  his  direction,  he  not  only  j 
appreciates  the  effect  and  justness  of  this  chord,  but  he  distinguishes  sepa-  j 
rately  all  the  notes  which  compose  it,  the  sounds  of  the  instruments  which  ; 
produce  it,  and  the  rhythm  of  the  music  under  execution. 

Is  its  delicacy  defective  in  distinguishing  the  various  species  of  sounds  or  | 
noises  that  it  hears,  and  in  deciding  what  are  the  bodies  which  produce  them? 
Does  not  a  needlewoman  distinguish  by  the  sound  whether  it  be  silk  or  cotton  j 
that  is  torn?  Is  not  the  peasant  aware,  long  before  he  perceives  anything, 
whether  the  sound  he  hears  is  that  of  a  diligence,  a  cabriolet,  or  a  cart,  and  j 
whether  they  be  loaded  or  empty  ?  Do  not  the  blind  recognize  the  ages  of 
persons  by  the  sound  of  their  voices? 

Is  its  precision  defective  in  appreciating  the  relations  which  sounds  bear  to 
each  other?  Oh,  in  this  respect  what  is  the  precision  of  the  eye  when  com-  j 
pared  with  that  of  the  ear?  If  we  ask  an  architect  habituated  to  linear  mea-  ; 
surements  the  relative  lengths  of  two  lines  neither  parallel  nor  situate  in  the 
same  plane,  should  he  err  only  by  a  thirtieth  part,  we  are  struck  by  the  cor¬ 
rectness  of  his  eye ;  but  to  the  ear  a  thirtieth  part  represents  more  than  a 
quarter  of  a  note.  Now,  a  practised  ear  which  hears  two  sounds  can  err  only  1 
by  a  four-hundredth  part,  or  about  the  forty-fifth  part  of  a  note. 

Finally,  is  its  promptitude  defective  in  seizing  sounds  which  pass  with 
rapidity,  and  whose  traces  are  lost  in  space?  Far  from  it,  since  the  preserva-  , 
tion  of  the  ear  is  chiefly  due  to  its  sensations  and  judgments  being  instan¬ 
taneous.  Let  a  sound  last  but  a  tenth  part  of  a  second,  it  is  known  and  better 


*  When  I  accorded  these  tuning-forks,  I  travelled  twelve  times  over  the  whole  extent  of  the  octave 
to  find  the  six  notes  1  wished  to  interpolnte  On  the  first  two  occasions  1  distinguished  nothing;  1  then 
caught  the  intervals  in  the  following  ordtr-  the  fourth,  the  fifth,  the  minor  sixth,  the  minor  third,  the 
major  sixth,  the  major  third,  the  minor  seventh,  the  major  seventh,  and,  with  great  pains,  the  major  I 
second  As  I  am  a  man  gifted  woth  a  musical  ear,  b  t  who  does  not  understand  music,  [  conclude  that  I 
il  there  exists  a  natural  ga  nut  tor  the  ear,  which  1  believe  to  he  a  fact,  it  is  the  minor  gamut,  and  not  the 
major 

A  protios  of  the  gamut,  I  stated  positively  that 't  is  not  true,  as  musicians  suppose,  that  a  sharp  note 
is  higher  than  the  flat  note  which  cortesponds  with  it.  For  a  long  time  I  successfully  defendtd  one  of 
the  numerous  mathematical  gamuts  by  means  of  experiments  appaientlv  very  conclusive,  when  M 
Barbereau,  professor  of  harmony,  took  the  trouble  of  coming  to  my  house,  for  the  express  purpose  of 
demonstrating  to  me  that  I  had  only  viewed  one  side  of  the  question.  He  agreed  witn  me,  in  the 
first  instance,  that  I  was  right  when  intervals  were  considered  separately,  but  that,  when  thevwere 
con  idered  as  regarded  melody,  I  was  completely  in  error  To  prove  this,  he  took,  on  my  sonometer, 
major  and  minor  thirds,  either  so  strong  or  so  feeble  as  not  to  be  endurable  to  the  ear  when  taken  by 
themselves;  then,  by  mtansof  melodies  sting  with  much  precision,  he  brought  out  these  thirds,  which 
I  found,  if  not  perfectly  just,  w'ete  at  all  events  very  tolerable  He  afterwards  made  analogous  experi¬ 
ments  on  the  sixths  with  the  same  results.  Thus,  thanks  to  his  kindness  (for  which  I  am  sincerely 
grateful),  1  learned  that  in  music,  as  in  painting,  it  is  taste  and  sentwunt  that  decide  what  is  art  properly  , 
so  celled,  and  not  geometry. 


THE  EAR. 


521 


known  than  if  it  lasted  for  a  minute ;  and  if  in  this  short  and  almost  indivisible 
interval  of  time  it  hears  simultaneously  many  sounds,  it  distinguishes  them 
all,  compares  them  all,  and  never  confounds  them. 

But  if  the  ear  be  thus  gifted,  as  beyond  all  doubt  it  is,  since  the  facts  1 
have  cited  maf  be  observed  and  verified  every  day,  how  does  it  happen  that 
persons  could  have  thought,  or  sometimes  think  still,  of  giving  to  it,  as  an 
auxiliary,  membranes  or  any  other  kind  of  artificial  ears?  Does  not  a  desire 
thus  to  aid  the  delicate  sensibility  of  the  ear  resemble  a  wish  to  give  light  to 
the  sun  by  a  candle  ? 

Let  us  learn  to  listen,  let  us  accustom  the  ear  to  listen  always,  and  to  listen 
to  everything.  Let  us  practise  it  in  the  analysis  of  the  sensations  it  expe¬ 
riences,  and  we  shall  find  that  all  the  faculties  of  the  ear  are  developed  by 
exercise,  that  several  of  them  invariably  become  more  perfect,  that  its  delicacy 
becomes  infinite,  its  precision  absolute,  its  fidelity  constant,  even  when  our 
judgment  deceives  us,  and  when  the  aid  it  can  afford  us  in  questions  of 
acoustics  can  only  be  limited  by  our  skill  in  using  it. 

For  twenty  years  I  suspected  these  truths  without  being  able  to  acquire 
sufficient  proofs  of  them,  and  consequently  without  daring  to  give  myself  up 
altogether  to  the  impressions  of  my  ear,  until  the  National  Exhibition  of  the 
Products  of  Industry  of  1849,  which  gave  me  an  opportunity  of  becoming 
assured  that  the  ear  is  exactly  what  I  had  imagined  it  to  be. 

During  the  concours  for  musical  instruments,  where  I  was  present  as  a 
member  of  the  central  jury,*  I  listened  to  the  instruments  with  my  back  turned, 
to  avoid  being  influenced  in  any  way:  for  although  the  makers’  names  on  them 
were  covered  with  numbered  tickets,  I  still  might  have  recognized  several  from 
having  seen  them  either  at  the  Exhibition  or  in  the  workshops,  and  thus  my 
judgment  might  be  warped.  Vain  precautions!  From  the  moment  a  piano¬ 
forte  maker  had  two  instruments  classified,  and  when  I  consequently  became 
acquainted  with  his  name,  I  recognized  nearly  all  the  various  kinds  of  instru¬ 
ments  he  afterwards  presented,  from  a  sort  of  regularity  or  uniformity  of  defects 
in  the  precision;  of  the  wind  instruments,  from  a  homogeneous  sound  of  the 
instruments  in  general,  but  chiefly  from  certain  shades  of  tone,  which  give  to 
all  kinds  of  instruments  by  the  same  maker  a  tolerably  characteristic  family 
resemblance,  so  that  an  attentive  and  practised  ear  cannot  be  mistaken  when 
it  compares  them  under  the  same  circumstances. 

I  was  in  an  excellent  position  for  testing  all  the  precious  qualities  I  attributed 
to  the  ear,  and  opportunities  could  not  be  wanting.  One  day,  while  they  were 
trying  the  wind  instruments,  1  heard  something  unforeseen  which  astonished 
me,  and  which  I  could  not  comprehend.  Fearing  on  the  instant  that  my 
attention  was  not  as  great  as  the  gravity  of  the  circumstances  required,  I  be¬ 
came  troubled,  the  blood  rushed  violently  to  my  head;  but  I  recovered  imme¬ 
diately,  and  my  attention  redoubled.  Shortly  after  I  saw  and  heard  nothing  of 
what  was  passing  around  me,  with  the  exception  of  the  subject  which  interested 
me.  From  that  moment  it  appeared  to  me  as  if  the  sound  produced  by  the 
fingers,  the  lips,  and  even  the  breath  of  the  artists  who  were  trying  the  instru¬ 
ments  penetrated  my  burning  ear  to  communicate  to  it  the  sensation  of  all  I 
wished  to  hear.  It  appeared  to  me  that  the  sensibility  of  my  ear  increased  as 


*1  believe  M.  Seguier  was  the  first  person  who  poposed  me  to  discharge  this  duty.  1  here  record  the 
testimony  of  my  eternal  gratitude  to  him  ter  having  powerfully  contributed  to  make  the  eat  know  n  to 

me 


522 


ACOUSTICS. 


its  tension  became  greater,  and  that  it  annihilated  all  my  other  senses  by  ab¬ 
sorbing  my  whole  existence.  I  imagined  that  I  heard  the  tone  of  an  instru¬ 
ment  the  instant  the  artist  laid  his  hand  on  it  to  take  it  up.  I  thought  I  could 
distinguish  the  instruments  made  in  the  new  or  in  the  old  establishments,  or 
in  those  where  the  workmen  are  frequently  or  are  seldom  changed.  I  thought 
I  could  recognize  instruments  made  expressly  for  the  concours,  or  which  were 
not  of  their  ordinary  mode  of  fabrication,  although  they  were  made  in  the 
establishment  which  presented  them.  I  thought  I  could  detect  a  difference 
in  the  tone  and  precision  of  the  same  wind  instrument  when  it  was  cold  or 
when  it  was  heated  by  the  hand  of  the  artist.  I  thought  I  could  hear  each 
note  accompanied  by  a  harmonic  sound,  and  preceded  by  another  higher  in 
the  scale.  I  thought  I  could  recognize  the  sounds  I  heard  five  years  before 
under  similar  circumstances,  when  I  was  present  as  an  amateur.  1  thought  I 
heard, —  I  still  listened.  But  we  cannot  fatigue  the  ear  with  impunity:  the 
effort  it  had  made  had  destroyed  its  sensibility,  and  I  do  not  suppose  that  it 
can  for  a  long  time  hence  be  submitted  to  a  similar  test. 

Did  I  hear  in  reality  all  that  I  imagined  I  heard  ?  Could  the  sensations  I 
experienced  arise  simply  from  great  nervous  excitement,  altogether  uncon¬ 
nected  with  imagination?  I  doubted  this  at  the  time,  but  I  am  now  convinced 
of  the  faithful  judgment  of  my  ear. 

If  all  that  I  have  just  said  suffice  to  show  that  the  ear  may  be  deemed  worthy 
of  consultation  in  acoustic  questions,  I  shall  doubtless  be  pardoned  fortracing 
here,  perhaps,  in  the  form  of  a  lecture,  the  path  to  follow  for  its  education ; 
but,  before  I  proceed  further,  I  wish  to  rectify  an  error  to  which  too  general 
credence  is  given. 

People  generally  imagine  that  a  good  ear  is  by  no  means  common,  and  fre¬ 
quently  persons  are  impressed  with  an  idea  that  they  have  no  ear  or  a  false 
ear.  Let  them  make  their  minds  easy  on  this  subject:  bad  ears  are  much 
rarer  than  good  ones.  Among  all  those  on  which  I  have  experimented — and 
the  number  is  great — I  never  met  with  one  even  defective.  1  found  some  little 
or  not  at  all  exercised,  some  practised  more  or  less,  some  more  or  less  sensible ; 
but  all  without  exception  were  susceptible  of  acquiring  a  high  degree  of  pre¬ 
cision  and  considerable  delicacy  by  education.  Now,  is  it  an  indifferent  matter 
at  what  age  we  commence  the  education  of  the  ear?  Unfortunately  not.  In 
infancy  the  ear  adapts  itself  to  all  the  exercises  we  make  it  undergo ;  its  pro¬ 
gress  is  rapid ;  its  sensibility  even  increases  by  habit ;  while  at  the  age  of  five- 
and-twenty  the  ear  is  less  obedient,  its  progress  is  slower:  it  can  doubtless 
still  arrive  (like  my  own  ear,  whose  defective  education  commenced  at  this 
age)  to  a  certain  degree  of  precision  and  delicacy;  but  frequently  it  will  meet 
with  difficulties  that  it  cannot  overcome.  It  would,  therefore,  be  most  desir¬ 
able,  for  the  interests  of  science,  and  even  for  that  of  musical  art  and  the 
fabrication  of  musical  instruments,  that  in  all  colleges  and  schools  the  ear  of 
the  pupils  be  practised,  not  precisely  to  make  them  musicians,  but  to  teach 
them  to  listen  and  to  understand  what  they  hear. 

For  the  purpose  of  hearing,  it  is  useless  to  listen.  In  its  normal  state  the 
ear  hears  constantly,  and  hears  everything.  To  distinguish  and  appreciate 
what  we  hear,  it  does  not  suffice  to  listen,  even  when  the  ear  is  practised;  we 
should  know  how  to  listen,  which  is  a  very  rare  acquirement.  When  the  ear 
is  struck  by  any  sound  or  noise,  its  attention  is  generally  directed  to  the  entire’ 
sound  at  once;  it  thence  follows  that  the  general  result  is  heard  without  any 
distinction  of  the  parts  which  compose  it,  and  that  we  become  acquainted  with 


EDUCATION  OF  THE  EAR. 


523 


tne  effect,  but  not  with  the  causes  which  gave  rise  to  it.  This  is  so  exactly 
true,  that  if  we  address  the  following  observation-to  the  major.ty  of  performers 
on  the  pianoforte,  “The  bass  notes  of  certain  pianos  are  disagreeable;  each 
note  is  accompanied  by  a  minor  seventh  or  a  major  ninth,”  they  will  tell  us, 
“  I  can  hear  nothing  of  the  kind.” 

That  is  not  true ;  for  when  we  strike  the  offending  notes  to  make  our  remark 
more  evident,  they  will  allow  that  they  heard  all  just  as  we  did  ourselves,  and 
sometimes  even  with  sufficient  distinctness  to  prove  disagreeable  to  the  ear. 
Thus,  then,  a  practised  ear,  from  not  knowing  how  to  listen,  may  sometimes 
not  distinguish  sounds  of  a  disagreeable  nature.  In  the  same  way,  when  the 
greater  number  of  musicians  test  the  qualities  of  an  instrument  (supposing 
them  neither  p-eoccupied  concerning  its  origin  nor  by  whom  it  was  manufac¬ 
tured),  what  they  exactly  appreciate  is  the  relation  which  the  instrument  bears 
in  its  ensemble  to  another  with  which  they  are  already  acquainted ;  but  as  to 
the  instrument  itself,  it  remains  unknown  to  them ;  whatever  its  defects  may 
be,  they  pass  unoerceived,  if  these  same  defects  are  usually  met  with  in  similar 
instruments.  They  hear  the  tone,  but  they  do  not  remark  the  relation  of  the 
harmonic  sounds  to  the  notes  which  they  accompany,  nor  the  sounds  of  the 
wood,  strings,  copper,  &c.,  which  characterize  the  tone;  and  this  arises  from 
their  not  knowing  how  to  listen,  for  they  hear  them  all. 

On  the  Education  of  the  Ear. 

The  first  thing  to  be  done  when  we  commence  the  education  of  the  ear  is  to 
teach  it  how  to  listen.  From  the  commencement,  we  should  habituate  our¬ 
selves  to  fix  all  the  attention  of  the  ear  on  a  single  sound  ;  thus,  when  we  hear 
several  sounds  or  noises  simultaneously,  we  should  listen  but  to  one;  when 
we  hear  two  sounds,  one  loud  and  the  other  feeble,  we  should  listen  only  to 
the  latter,  and  try  to  be  deaf  to  the  former.  We  should  habituate  ourselves 
to  listen  in  what  manner  sounds  begin,  and  how  they  end ;  and  also  to  lend 
the  car  much  less  to  what  we  hear  than  to  what  we  imagine  we  do  not  hear, 
and  never  to  listen  more  than  an  instant  to  the  same  thing.  For  the  moment, 
these  exercises  will  not  teach  us  much  ;  but  we  should  constantly  practise 
them  until  from  habit  they  become  familiar. 

While  we  are  engaged  with  these  exercises,  we  should  teach  the  ear  to  dis¬ 
tinguish  musical  intervals.  This  generally  appears  somewhat  startling,  as  the 
greater  number  of  students  learn  music  for  three  or  four  years  without  being 
acquainted  with  them,  and  for  this  excellent  reason  —  that  they  receive  no 
instruction  on  the  subject.  By  beginning  the  study  of  musical  intervals  at  the 
age  of  twenty-five  years,  it  requires  six  or  eight  months  to  become  well  ac¬ 
quainted  with  them  when  we  devote  to  these  studies  one  hour  each  day.  This 
is  something,  I  am  aware;  but  it  is  also  something  to  have  a  practised  ear  if 
we  should  require  it. 

As  to  the  method  to  be  adopted  in  the  study  of  intervals,  I  think  I  cannot 
do  better  than  to  indicate  that  followed  by  M.  Duchemin,  director  of  musical 
instruction  in  the  asylums  (sailes  d'asile )  of  Paris,  by  reason  that  the  results 
which  1  witnessed,  when  he  tried  his  method  of  musical  instruction  at  my 
house,  left  nothing  to  be  desired. 

M.  Duchemin,  setting  aside  all  ideas  of  notation,  commences  by  demon¬ 
strating  to  the  pupil,  by  means  of  any  musical  instrument  whatever,  the  interval 
of  a  note  and  that  of  half  a  note.  After  the  pupil  has  been  sufficiently  in¬ 
structed  in  the  distinction  of  these  intervals,  he  makes  him  listen  to  the  interval 


ACOUSTICS. 


524 


of  a  note  and  to  that  of  a  major  third.  He  next  makes  him  compare  the 
major  third  with  the  fourth,  and  thus  successively  all  the  major  intervals  of  the 
same  octave.  He  then  returns  to  the  point  from  which  he  started,  and 
makes  him  compare  the  major  with  the  minor  intervals.  When  the  pupil  is 
acquainted  with  all  the  ascending  intervals,  he  recommences  the  same  exer¬ 
cises  as  above,  but  in  descending.  Finally,  when  the  pupil  has  compared  all 
the  intervals  by  two  and  two,  M.  Duchemin  makes  him  listen  to  isolated 
intervals,  either  ascending  or  descending;  at  first  those  comprised  within  a 
single  octave,  afterwards  within  two  octaves,  &c. 

If  the  knowledge  of  musical  intervals  thus  obtained  be  sufficient  for  the 
musician,  it  is  not  so  for  the  professor  of  physics.  It  does  not  suffice  for  him 
to  be  aware  when  an  interval  is  true  or  false,  or  even  when  it  is  too  great  01 
too  small ;  he  must  be  capable  of  estimating  almost  exactly  to  what  degree 
it  be  too  great  or  too  small.  Neither  does  it  suffice  for  him  to  be  capable  of 
comparing  the  notes  produced  by  musical  instruments;  for, -as  sound  to  him 
represents  every  sensation  of  the  ear  that  arises  from  any  vibratory  motion 
whatever,  he  will  hear  them  of  every  kind,  as  regards  their  tone,  their  intensity, 
their  duration,  their  sharpness,  &c.;  he  will  even  frequently  be  forced  to  sepa¬ 
rate  and  to  compare  sounds  which  have  neither  the  same  tone,  intensity,  or 
duration,  and  he  then  requires  a  great  accuracy  of  ear  and  long  experience 
to  keep  free  from  errors.  It  becomes,  therefore,  necessary  to  resume  the  study 
of  intervals ;  but  now  no  instructor  is  required,  and  some  of  the  experiments 
may  be  performed  without  seriously  occupying  our  time. 

At  present  each  interval  is  to  be  compared  with  itself,  by  taking  it  true  in 
one  case  and  more  or  less  altered  in  the  other.  For  this  purpose  we  make 
use  of  a  sonometer,  divided  so  as  to  enable  us  to  take  exact  intervals,  and  at 
the  same  time  to  make  known  to  us  the  numerical  difference  existing  between 
the  true  interval  and  this  same  interval  when  altered.  (My  differential  sono¬ 
meter  is  well  adapted  to  this  purpose ;  indeed,  I  called  it  by  this  name  because, 
from  the  date  of  its  first  construction,  I  used  it  for  this  object.)  And  as  it  is 
required  to  hear  the  two  sounds  of  the  same  interval  in  the  shortest  possible 
space  of  time,  and  to  hear  them  often  repeated  simultaneously,  to  accustom 
the  ear  to  this  sensation,  we  begin  by  tuning  to  unison  the  two  strings  of  the 
sonometer,  to  enable  us  to  take,  by  means  of  movable  bridges,  the  first  note 
on  one  string  and  the  second  on  the  other.  Then  we  compare  the  true  interval 
at  first  with  the  interval  altered  to  the  maximum,  that  is  to  say,  about  a 
quarter  of  a  note  either  higher  or  lower,  and  we  continue  the  comparison  by 
gradually  diminishing  the  difference  to  zero,  but  always  commence  the  experi¬ 
ment  by  listening  to  the  true  interval.  It  is  not  with  a  fiddle-bow  that  we 
sound  the  strings  in  these  experiments,  but  with  the  fingers,  and  always  feebly, 
by  reason  that  wre  can  better  appreciate  sounds  that  are  low  and  of  short  dura¬ 
tion  titan  we  can  those  which  are  loud  and  long-continued.* 

We  can  easily  comprehend  that  by  means  of  these  experiments  the  ear  not 
only  learns  to  estimate  the  relation  of  two  sounds  with  tolerable  precision,  but, 
moreover,  it  becomes  habituated  to  the  most  rigorous  exactness. 

We  have  hitherto  only  learned  to  recognize  the  intervals  of  notes  which 
are  very  distinct  and  always  of  the  same  nature,  since  they  were  produced 

*  The  sounds  that  the  ear  appreciates  most  easily  are  those  comprised  w  ithin  the  diapason  of  the  human 
voice  :  those  which  it  judges  best  are  sounds  of  a  feeble  but  invariable  intensity;  for.  strange  to  say,  the 
ear,  in  other  respects  so  just,  is  ahvavs  inclined  to  believe  that  a  sound  becomes  lower  when  its  intensity 
increases. 


EDUCATION  OF  THE  EAR. 


525 


by  the  same  instrument.  This  is  not  enough ;  we  must  also  be  able  to  ap¬ 
preciate  the  intervals  of  sounds  which  have  but  little  distinctness,  and  even 
those  which  exist  between  two  sounds  of  different  kinds.  For  this  purpose 
there  is  no  further  necessity  for  instruments  or  for  regular  studies ;  it  suf¬ 
fices  to  consider  the  subject  at  our  leisure,  and  to  seize  on  such  opportu¬ 
nities  as  may  present  themselves.  For  example,  if  we  sit  alone  at  table,  we 
may  compare  the  sound  of  a  glass  or  of  a  decanter  with  that  of  a  bottle.  If 
we  have  at  hand  two  bottles  unequally  rilled,  we  may  blow  on  the  edges  of 
their  apertures :  the  sounds  which  result  will  be  feeble,  but  will  still  be  very 
ap;  r.-ciable  even  to  unpractised  ears.  At  our  fireside,  we  may  compare  the 
sound  of  the  fire-shovel  with  that  of  the  tongs.  In  a  word,  according  to  the 
circumstances  in  which  we  may  be  placed,  we  can  use  for  this  investigation  all 
objects  capable  of  yielding  sounds.  By  employing  daily  some  of  our  leisure 
moments  with  these  exercises,  apparently  very  innocent  and  futile,  the  ear  will 
insensibly  become  accustomed  no  longer  to  hear  noises ,  but  always  to  hear 
sounds ,  and  sounds  whose  mutual  relation  it  will  perfectly  comprehend. 

So  long  as  sounds  have  the  same  tone,  no  matter  how  short  be  their  dura¬ 
tion,  how  defined  or  even  sharp  they  may  be,  their  relations  can  always  be 
observed  with  tolerable  ease.  Everybody  can  recognize  a  gamut  resulting 
from  the  noises  produced  by  eight  pieces  of  wood  (cut  until  they  accord  with 
an  octave  of  musical  notes)  when  they  are  thrown  on  the  floor,  although  the 
tone  resulting  from  the  fall  of  any  single  piece  be  inappreciable  to  musicians ; 
but  this  is  no  longer  the  case  when  the  sounds  have  different  tones,  especially 
when  they  are  not  well  defined:  in  these  instances  it  is  extremely  easy  for  an 
ear,  unless  it  be  highly  practised,  to  be  deceived  by  an  octave,  and  even  to 
confound  the  octave  with  the  fifth  when  the  interval  exceeds  three  octaves. 

Finally,  there  remains  something  to  be  done  which  is  neither  the  least  im¬ 
portant  or  the  most  easy,  and  this  is  the  exercise  of  the  ear  in  the  analysis  of 
sounds.  It  is  no  difficult  matter  for  a  musician  to  analyse  a  chord,  because,  in 
the  first  place,  all  chords  are  familiar  to  him,  and,  in  the  next,  because  the  notes 
of  which  it  is  composed  are  always  very  distinct,  and  are  produced  by  instru¬ 
ments  with  whose  tones  he  is  acquainted  ;  but  to  analyse  a  chord  or  mixture 
of  sounds  when  we  often  imagine  we  hear  but  a  single  one — and,  moreover, 
having  no  data  to  guide  us  in  our  researches  for  those  we  imagine  may  accom¬ 
pany  it,  we  propose  to  ourselves  not  merely  to  discover  the  relations  existing 
between  them,  but  still  further  to  determine  their  origin,  as  well  as  the  causes 
which  gave  rise  to  them — is  a  very  different  affair.  Here  the  habit  of  hearing 
sounds  will  no  longer  suffice;  we  must  know  how  to  listen  to  them,  and  have 
studied  them. 

All  that  1  can  do  here  is  to  indicate  the  exercises  which  should  be  adopted 
for  learning  to  distinguish  one  or  several  feeble  sounds  when  they  are  con¬ 
nected  with  a  louder  one.  I  shall  then  enter  on  some  considerations  respecting 
sound,  where,  among  the  observations  I  shall  have  occasion  to  make,  may  be 
found  certain  data  which  will  frequently  be  of  use  in  the  solution  of  questions 
of  this  nature. 

For  the  first  exercise  we  select  a  note  neither  too  low  nor  too  high,  and  as 
pure  as  possible,  as,  for  example,  that  of  an  open  organ-tube  between  the 
notes  ut  2  and  ut  3,  or  that  of  my  tuning-fork  mounted  on  its  stand.  To  this 
sound  we  add  another  well  known  beforehand,  but  differing  in  tone  and  by  an 
interval  either  true  or  false,  such  as  a  note  taken  at  hazard  on  a  violin  or  on 
a  plate  or  blade  of  metal.  While  we  hear  these  two  sounds  s:multaneously, 


526 


ACOUSTICS. 


we  should  listen  only  to  the  higher  note,  which  should  be  gradually  weakened 
by  removing  it  to  a  distance,  or  by  other  means  according  to  its  nature,  until 
we  cease  to  distinguish  it,  which  ought  only  to  be  when  we  cease  to  hear  it. 
We  may  perceive  that  this  sound  is  still  very  distinct  to  the  ear  so  long  as 
we  can  take  its  unison  on  the  sonometer.  We  should  recommence  this  exer¬ 
cise,  always  changing  the  higher  note,  until  the  ear  is  sure  of  the  interval,  no 
matter  how  feeble  the  tone  may  be. 

We  may  renew  these  experiments,  using,  if  we  please,  the  same  instruments 
as  we  did  before,  provided  we  change  the  lower  note ;  but  now  the  higher  note 
that  we  add  ought  to  be  unknown — that  is  to  say,  it  should  not  have  been 
heard  alone  previous  to  the  experiment ;  it  should  be,  moreover,  continuous 
and  feeble  in  proportion  to  the  lower  note,  that  it  may  be  placed  precisely  in 
the  conditions  of  the  harmonic  and  other  sounds  which  always  accompany 
the  principal  note.  The  two  notes  being  thus  heard,  we  should  try  to  appre¬ 
ciate  their  interval,  and  at  the  same  time  the  tone  of  the  upper  note. 

When  we  have  attained  the  instruction  requisite  for  analysing  a  mixture  of 
two  sounds  differing  in  tone  and  intensity,  we  should  employ  the  same  means 
in  learning  to  analyse  a  mixture  of  three  sounds;  and  here  we  may  stop.  The 
habit  acquired  of  listening  will  accomplish  whatever  remains  to  be  done;  for 
one  of  the  attributes  of  the  ear  being  to  hear  always  without  any  participa¬ 
tion  of  our  will,  it  follows  that,  having  once  contracted  a  habit  of  listening,  it 
listens  almost  without  our  being  aware  of  it.  Thus,  without  thinking  of  it, 
when  we  hear  a  drinking-glass  struck  by  the  blade  of  a  knife,  we  distinguish 
three  sounds — the  fundamental  note  and  the  first  harmonic,  whose  interval 
varies,  according  to  the  form  and  proportions  of  the  glass,  from  the  minor 
sixth  to  the  major  tenth,  and,  besides,  the  second  harmonic,  which  is  very 
feeble  and  much  higher. 

When  we  hear  a  string  of  moderate  length  resound,  we  may  distinguish  a 
suite  of  harmonics,  and  remark  that  these  sounds  vary  according  to  the  por¬ 
tion  of  the  string  on  which  we  operate,  and  the  mode  we  adopt  to  produce  the 
vibrations. 

When  we  hear  a  drum,  we  remark  first  a  low,  uncertain,  and  confused  note, 
which  is  that  of  the  air  it  encloses  :  then  a  series  of  clearer  and  better  defined 
notes,  announcing  a  more  easy  mode  of  vibrations;  this  is  the  fundamental 
note  of  the  membrane  and  its  harmonics,  among  which  we  frequently  distin¬ 
guish  a  tolerably  agreeable  ninth  or  tenth.  We  may  besides  remark  a  great 
number  of  harmonics,  very  high  in  the  scale  and  of  short  duration  :  they  are 
produced  by  the  action  of  the  chords  on  the  inferior  membrane;  and,  finally, 
we  recognize,  by  a  sort  of  metallic  tinkling,  the  sound  produced  by  the  brass 
cylinder  of  the  drum. 

One  word  more  on  the  analysis  of  sounds.  When  a  tuning-fork  is  mounted 
on  a  hollow  stand  which  yields  a  note  in  unison  with  it  (as  I  have  constructed 
this  instrument),  it  is  easily  put  in  action  by  the  slightest  vibratory  motion 
which  the  air  contained  in  its  stand  may  receive  from  any  extraneous  sound; 
but,  as  substances  vibrate  sympathetically  only  from  the  influence  of  their 
unison,  it  follows  that  the  tuning-fork  is  deaf  to  all  sounds  excepting  its  own, 
to  which  it  instantly  replies  with  more  or  less  energy,  according  as  the  sounds 
are  more  or  less  identified,  as  they  are  nearer  or  farther  from  each  other,  and 
as  the  sound  is  more  or  less  intense.  If,  then,  a  tuning-fork  thus  mounted  be 
placed  in  the  proximity  of  any  sound  accompanied  by  a  harmonic  in  unison 
with  the  tuning-fork,  this  lattei,  by  vibrating,  instantly  announces  the  fact. 


CONSIDERATIONS  ON  SOUND. 


5n 


Far  from  me  I  reject  the  idea  of  proposing  such  a  method  of  supplying  the 
ear.  1  know  the  ear  too  well.  Nevertheless,  I  have  used  it,  and  often  with 
success,  but  only  in  cases  where  I  suspected  a  sound  to  be  accompanied  by  its 
upper  octave,  which  I  was  unable  to  distinguish,  less  from  its  weakness  than 
from  its  perfect  consonance  with  the  principal  note. 

It  was  by  this  method  that  I  found  the  notes  of  the  human  voice  from  the 
chest  are  always  accompanied  by  the  upper  octave  and  by  the  double  octave. 

Considerations  on  Sound. 

There  exists  no  simple  sound  ;  all,  without  exception^  are  accompanied  by  a 
mixture  of  other  sounds  more  or  less  appreciable  to  the  ear,  varying  according 
to  the  number  of  those  which  compose  it,  to  their  respective  relations,  and  to 
the  mode  of  vibrations  which  give  rise  to  them,  and  according  to  the  size, 
form,  and  description  of  matter  which  produces  them.  Furthermore,  if  the 
sounding  body,  from  its  size,  shape,  or  nature,  be  capable  of  easily  yielding 
two  sounds  of  the  same  description— I  mean,  arising  from  a  similar  mode  of 
vibration — we  never  hear  the  lower  sound  without  its  being  preceded  by  the 
higher,  except,  perhaps,  when  its  vibration  is  induced  by  the  influence  of  a 
unison.  And  if  it  can  readily  yield  many  sounds  of  the  same  kind,  the  first 
harmonics,  like  the  fundamental  note,  will  always  be  preceded  by  other  har¬ 
monics  higher  in  the  scale. 

The  series  of  experiments  which  led  me  to  these  observations  are  the  fol¬ 
lowing: — In  the  second  edition  of  my  catalogue  I  inserted  a  few  words  respecting 
a  very  remarkable  experiment  of  M.  Delezenne  on  strings  in  vibration,  and  of 
the  conclusions  drawn  thence  by  M.  Duhamel  and  by  myself. 

M.  Delezenne  showed  me,  in  1842,  that  it  is  impossible  to  make  a  string  sound 
by  drawing  a  bow  across  its  centre.  M.  Duhamel,  to  whom  I  mentioned  this 
circumstance,  suspected  that,  in  a  string  which  yields  the  fundamental  note, 
the  first  harmonic  oscillates,  and  that  the  note  cannot  be  developed,  because 
the  bow  prevents  the  motion  when  applied  to  the  middle  of  the  string.  To 
verify  his  hypothesis,  M.  Duhamel  tried  to  make  the  string  resound  by  means 
of  two  bows  moving  in  the  same  direction,  and  placed  on  the  right  and  left  of 
the  centre  of  the  string:  no  sound  resulted.  When,  on  the  contrary,  he  drew 
the  two  bows  across  the  same  portions  of  the  string,  but  in  opposite  directions, 
the  fundamental  note  was  instantly  developed,  and  accompanied  by  the  first 
harmonic.  Although  this  ingenious  demonstration  did  not  admit  of  a  reply, 
yet  I  did  not  long  remain  convinced.  I  could  not  comprehend  why  the  first 
harmonic  was  more  necessary  to  the  development  of  the  fundamental  note  of 
the  string  than  any  other  harmonics  higher  in  the  scale  which  we  commonly 
hear  during  the  entire  duration  of  a  sound.  I  then,  in  accordance  with  the 
established  custom,  abandoned  the  ear  for  the  eyes.  I  endeavoured,  on  the 
monochord  of  Savart,  to  make  the  string  yield  the  fundamental  note  by  draw¬ 
ing  the  bow  near  its  centre.  1  succeeded,  and  I  saw  two  chords  or  divisions, 
with  a  node  of  vibration  in  their  centre.  M.  Duhamel  was  again  right. 

I  afterwards  operated  on  the  string  near  the  other  harmonic  divisions  in 
succession,  and  always  procured  the  fundamental  note.  Thus,  when  I  operated 
near  the  third  of  its  length,  I  saw  three  chords  or  divisions,  each  with  a  node 
of  vibration  at  the  third  of  its  length.  By  operating  near  the  quarter  of  its 
length,  I  saw  four  divisions;  near  the  fifth,  five;  and  so  on.  Then,  laying  aside 
this  instrument,  which  yields  no  sound,  to  use  my  differential  sonometer  in  its 
stead,  and  to  appeal  to  the  judgment  of  the  car,  I  recognized,  in  fact,  that  by 


$28 


ACOUSTICS. 


Fig.  435. —  The  Monochord , 


Showing  the  ventral  segments,  or  tho«e  portions  of  the  strings  which  are  the  most  violently  agitated, 
anil  therefore  throw  off'  the  paper  riders,  whilst  they  remain  quiescent  at  the  nodal  points. 

acting  on  the  string  near  the  third  of  its  length,  we  hear  with  almost  equal 
intensity  the  twelfth  and  the  fundamental  or  key-note.  When  we  act  near  the 
quarter  of  its  length,  we  hear  the  double  octave ;  near  the  fifth,  the  major 
seventeenth,  &c.  And  what  is  worthy  of  remark,  the  harmonic  always  pre¬ 
cedes  the  key-note.* 

From  these  experiments  we  find  that  the  harmonic  which  of  necessity 
accompanies  the  fundamental  note  is  not  always  the  first,  but  is  that  which 
corresponds  to  the  nearest  division  to  the  part  acted  on.  It  hence  results  that 
a  string  perfectly  free  from  all  foreign  influence  cannot  be  made  to  resound 
by  the  bow,  not  only  when  we  act  on  its  centre,  but  still  further  when  we 
operate  on  any  of  its  harmonic  divisions,  as  may  be  shown  by  my  apparatus 
for  the  longitudinal  vibration  of  strings. 

All  that  has  been  stated  with  respect  to  the  emission  of  the  fundamental 
note  of  a  string  vibrating  transversely  is  applicable  to  harmonic  sounds,  at 
least  within  the  limits  of  possibility — that  is  to  say,  all  the  experiments  made 
on  the  whole  string  yielding  the  fundamental  note  may  be  repeated  on  a  por¬ 
tion  of  it  yielding  a  harmonic  note,  only  the  phenomena  will  be  less  sensible, 
by  reason  that  the  portions  of  the  string  which  remain  free  influence  in  a 
greater  or  less  degree  that  which  we  act  on ;  and,  besides,  the  noi.es  are  pro- 


*  The  notes  called  harmonics  are  thus  called  from  their  accordance  and  harmonious  relations  to  each 
other.  The  number  of  their  vibrations  are  to  each  other,  when  produced  in  tubes  open  at  both  ends, 
as  the  natural  suite  of  numbers,  1,  2,  t,  4,  &c.  Thus,  1  representing  the  fundamental  note,  the  first 
harmonic  to  this  note  will  be  its  upper  octave;  for  the  vibrations  of  the  upper  octave  of  any  note  are 
always  double  those  of  that  note.  The  next  harmonic  vibrates  three  times  as  often  as  the  key-note;  the 
fourth,  four  times,  8cc. 

These  harmonics  can  easily  be  produced  on  the  German  flute.  Thus,  when  all  the  holes  and  keys  of 
the  flute  are  shut,  if  it  be  made  to  sound,  and  the  lorce  of  inflation  be  constantly  increased,  it  first  yields 
lit  the  key-note,  next  ut  the  octave,  next  sol,  next  ut  the  double  octave,  next  wi,  and,  afterwards,  la. 


The  harmonics  produced  by  a  tube  closed  at  one  end  are  as  the  numbers  t,  3,  J,  7,  &c.,  which  evi. 
dent'y  accord  with  each  other,  as  we  find  them  all  in  the  harmonics  produced  in  open  tithes. 


CONSIDERATIONS  ON  SOUND. 


529 


portionately  less  appreciable  to  the  ear,  as  they  are  higher  and  more  feeble. 
Thus,  for  example,  if  we  try  to  sound  the  first  harmonic  of  a  string  (even  when 
isolated  as  much  as  possible)  by  lightly  placing  a  finger  on  the  middle  of  the 
string  and  drawing  the  bow  across  the  centre  of  one  of  the  halves,  instead  of 
hearing  nothing,  as  in  the  former  instance,  we  shall  hear  this  harmonic  a  little, 
although  it  be  imperfectly  articulated,  because,  the  other  half  of  the  string  re¬ 
maining  free,  there  is  nothing  to  impede  its  division,  if  not  into  two,  at  all 
events  into  three  portions,  and  it  may  consequently  yield  some  sort  of  sound. 

In  the  same  way,  if  we  act  on  one  of  the  halves  of  the  string  near  its  centre 
to  make  it  resound,  there  will  be  no  reason  why  the  first  harmonic  should  be 
accompanied  by  the  second  rather  than  the  third,  since  there  is  nothing  to 
prevent  these  divisions  in  the  other  half  of  the  string.  But,  no  matter  what 
be  the  circumstances  which  favour  the  development  of  this  sound,  we  never 
hear  it  unless  it  be  preceded  and  accompanied  by  a  higher  harmonic  note;  and 
this  is  equally  true  as  regards  the  third  and  other  harmonics  higher  in  the 
scale,  so  long  as  these  notes  are  perceptible  to  the  ear. 

We  have  said  enough  on  this  subject.  It  suffices  to  have  demonstrated 
here  that  a  string  on  which  we  act  transversely  can  resound  only  on  the  con¬ 
dition  that  it  can  yield  at  least  two  transverse  sounds,  of  which  the  higher  will 
depend  on  the  part  acted  on,  or  on  the  mode  of  inducing  the  vibrations. 

Every  string  which  vibrates  transversely  between  two  fixed  points  vibrates 
longitudinally  at  the  same  time :  this  is  evident  from  the  fact  that  it  cannot 
deviate  from  a  straight  line  without  being  lengthened,  or  return  to  a  straight 
line  without  being  shortened.  The  sound  thence  resulting  is  almost  insensible 
in  musical  instruments,  and  even  in  the  sonometer,  because  the  bridge  being 
incapable  of  arresting  the  longitudinal  vibratory  motion,  it  is  transmitted  to 
the  portion  of  the  string  beyond  it,  which  renders  this  sound  very  variable  and 
prevents  its  development.  It  may  sometimes,  however,  be  heard,  though 
considerably  altered,  in  the  la  of  the  violoncello,  as  persons  who  learn  to  play 
on  this  instrument  are  well  aware,  although  they  cannot  account  for  it.  It  is 
the  sound  which,  when  well  articulated,  is  known  in  the  language  of  musicians 
by  the  term  canard. 

When  the  string,  on  the  contrary,  vibrates  between  two  fixed  points,  as  in 
the  apparatus  for  longitudinal  vibrations,  then  when  we  act  on  it  with  the  bow, 
or  when  we  strike  it,  the  longitudinal  sound  accompanies  the  transverse  one  as 
long  as  it  lasts,  and,  if  we  listen  attentively  when  we  sound  the  first  harmonic 
transversely,  we  shall  hear  equally  the  longitudinal  sound  of  half  the  string. 

Independently  of  these  two  different  modes  of  vibration,  every  string  which 
vibrates  tranversely  executes  a  third,  which  is  inseparable  from  the  two  others. 

Let  us  hang  on  the  middle  of  a  string  a  very  thin  brass  wire,  bent  like  the 
figure  8,  supporting  on  one  of  its  rings  a  little  cone  of  paper,  while  the  other 
encloses  the  string  without  pressing  on  it;  let  us  then  make  the  string  vibrate 
transversely,  either  with  the  bow  or  by  striking  it,  and  we  shall  immediately 
observe  the  cone  to  turn  round  with  an  extreme  rapidity,  then  return  and  re¬ 
volve  in  the  opposite  direction,  and  change  in  this  manner  ten  or  twelve  times, 
if  it  be  lightly  constructed.  And,  to  observe  this  phenomenon,  it  is  by  no  means 
necessary  to  bring  out  the  key-note  of  the  string:  the  cone  will  turn  in  the 
same  way  at  the  ventral  points  of  vibration  of  the  first,  the  second,  and  even 
the  third  harmonic ;  and  if,  instead  of  one  cone,  we  suspend  two  on  the  string, 
"e  remark  that,  when  they  are  placed  on  two  consecutive  divisions,  they  turn 
in  opposite  directions. 


53° 


ACOUSTICS. 


Now,  to  determine  this  phenomenon,  it  is  evident  that  the  string  must,  in 
vibrating,  assume  a  rotatory  motion,  for  the  cone  turns  round  it;  and  also 
that  this  rotatory  motion  arises  from  a  twisting  of  the  string,  for  the  cone  re¬ 
volves  periodically  in  opposite  directions.* 

It  results  from  all  that  has  been  said,  that  a  string  which  vibrates  trans¬ 
versely  is  forced  to  execute  at  least  four  different  vibratory  motions,  viz.,  two 
transverse,  as  I  have  already  explained,  one  longitudinal,  and  an  alternating 
rotatory  motion.  Now,  if  we  add  to  these  the  different  accidental  vibratory 
motions  which  arise  from  various  transformations,  that  is  to  say,  those  which 
give  rise  to  a  multitude  of  harmonics  of  all  kinds,  which  we  invariably  hear 
when  the  string  is  long,  we  find  that  a  string  of  medium  length  which  sounds 
transversely  may  often  simultaneously  execute  ten  or  tw  elve  different  vibratory 
motions. 

If  the  simultaneous  concurrence  of  several  different  vibratory  motions  be 
indispensable  for  the  production  of  sound  in  a  string,  this  concurrence  is  not 
ess  essential  to  the  production  of  sound  in  any  other  substance,  no  matter 
w'hat  be  its  form  or  nature ;  for  although  I  have  for  eight  years  sought  to  dis¬ 
cover  a  simple  sound,  yet  I  have  found  none :  all  the  sounds  I  hear  are  pre¬ 
ceded  and  accompanied  by  one  or  more  harmonics,  arising  from  one  or  from 
several  modes  of  different  vibrations,  whose  relations  with  the  principal  sound 
vary  according  to  the  nature  and  form  of  the  vibrating  substance,  and  also 
frequently  from  the  point  acted  on.  and  the  method  used  to  excite  its  vibra¬ 
tions.  From  thence  is  chiefly  derived  the  variety  of  tones  produced  by  sub¬ 
stances  which  vary  in  form  and  nature,  as  also  the  difference  whicli  frequently 
exists  in  the  tone  of  the  same  sound  produced  by  the  same  substance  when  it 
is  acted  on  at  different  points  or  set  in  vibration  by  different  means.  In  solid 
bodies  a  sound  produced  by  a  shock  has  rarely  the  same  tone  as  when  the 
sound  is  produced  by  a  bow,  because  the  action  of  the  bow  often  prevents  the 
spontaneous  development  of  certain  harmonics  from  transformations  of  mo¬ 
tion,  while,  at  the  same  time,  it  gives  rise  to  others,  which  persist  as  long  as 
its  action  is  continued,  as  is  exemplified  in  the  case  of  strings.  In  the  columns 
of  air  which  only  yield  harmonics,  as  in  the  French  horn,  the  trumpet,  the 
trombone,  and  all  the  instruments  d  piston,  the  tone  is  very  different  from  that 
which  we  observe  in  columns  of  air  which  yield  the  fundamental  note,  as  in  the 
flute,  the  clarionet,  the  ophicleide,  &c. ;  in  the  first  place,  because  the  embou¬ 
chure  has  a  great  influence  on  the  tone,  and,  next,  because  in  the  former  instru¬ 
ments  the  vibrations  are  only  longitudinal,  whereas  in  the  latter  they  are  mixed, 
as  we  shall  find  hereafter;  consequently,  the  same  note  taken  in  the  two  dif¬ 
ferent  cases  may  not  be  accompanied  by  the  same  harmonics. 

Thus,  when  we  wish  to  ascertain  the  different  vibratory  motions  coexisting 
in  a  vibrating  substance,  and  when  we  judge  merely  by  the  ear,  we  must 
necessarily  take  into  account  the  manner  in  which  these  vibrations  are  excited. 


*  This  fact  explains  what  I  was  lone;  in  search  of,  namelv,  why  the  air  enclosed  in  a  violin  resounds 
under  the  action  of  the  bow.  Savart,  after  having  demonstrated  that,  when  a  system  is  put  into  a  state 
ol  vibration,  the  vibratory  motion  is  propagated  throughout  all  its  parts  parallel  to  the  axis  of  the  motion 
impressed  on  it,  was  already  occupied  about  this  question,  and,  after  manv  ingenious  experiments  on  the 
sounding-post  of  the  violin,  he  came  to  the  conclusion  that  its  function  was  to  transform  into  normal 
vibrations  the  tangential  vibrations  which  the  bow  impiesses  on  the  bridge  But  when  we  suppress  the 
sounding  post  of  a  violin,  if  it  have  less  sound  than  it  had  btfore,  it  has  still  a  hundred  times  as  much 
as  when  we  suppress  the  under  board  of  the  violin  (“  fotui  ,iu  violnn”),  as  we  may  easily  believe  without 
needing  to  repeat  the  experiment.  Then,  if  the  enclosed  air  still  acts  with  energy,  it  is  evidently  be¬ 
cause  the  rotatory  movement  of  t  rsion  in  the  string  renders  the  transverse  vibrations  sometimes 
tangential  to  the  bridge  and  sometimes  perpendicular  to  it. 


CONSIDERATIONS  ON  SOUND. 


53i 


It  would  likewise  be  necessary  in  experimenting  to  have  a  locality  perfectly 
adapted  to  this  kind  of  observation,  and  with  whose  acoustic  properties  we 
should  be  well  acquainted.  Questions  connected  with  sound  are  already  so 
complex  that  we  cannot  take  too  many  precautions  to  prevent  any  disturbing 
causes  still  further  complicating  the  phenomena. 

In  experimenting  in  a  room,  I  have  often  observed  that  a  double  reflection 
suffices  to  produce  beatings  ( battements )  with  the  sound  or  with  one  of  its 
harmonics,  so  as  to  excite  a  suspicion  of  two  sounds  nearly  identical  where 
there  is  only  one. 

I  also  discovered  that  a  certain  intensity  of  a  transverse  harmonic  may  be 
attributed  to  longitudinal  vibrations,  when  this  intensity  is  merely  due  to  a 
coincidence  of  vibrations  between  this  harmonic  and  a  subdivision  of  the  air 
or  any  other  matter  contained  in  the  room. 

It  again  happens  that  we  may  imagine  we  cause  the  air  enclosed  in  the 
“ caisse"— the  body  of  the  violin — to  resound,  while  in  reality  we  only  make 
sound  a  harmonic  of  the  room;  or  that,  in  seeking  to  communicate  a  vibra¬ 
tory  motion  to  a  solid  or  liquid,  we  determine  in  a  contiguous  mass  of  air  a 
sound  totally  different  from  that  we  imagine  we  hear. 

Very  frequently  also  we  are  exposed  to  the  chance  of  allowing  many  feeble 
sounds  to  escape  us,  which  would  be  very  appreciable  to  the  ear  if  it  were  not 
unceasingly  troubled  and  incommoded  by  noise  from  without,  which  we  ima¬ 
gine  we  do  not  hear,  because  we  hear  it  always. 

And  yet  what  have  we  done,  up  to  the  present  time,  to  prevent  the  causes  of 
these  errors,  and  probably  many  others  that  are  still  unknown?  Nothing  that 
I  know  of.  It  would  even  appear  that  they  were  never  given  a  thought. 
People  experiment  indifferently  in  one  place  or  another,  which,  to  speak  the 
truth,  imports  but  little,  since  we  are  aware  of  none  suited  for  acoustics. 

Well,  I  ask,  if,  before  we  endeavour  to  penetrate  this  labyrinth  of  errors  and 
deceptions,  it  would  not  be  reasonable  to  turn  our  steps  backward,  to  act  as  if 
we  believed  we  knew  nothing  of  sound,  and  commence  a  serious  investigation 
of  all  the  phenomena  that  sound  may  offer  us  in  space,  whether  limited  or 
indefinite,  when  freely  transmitted  through  the  air  or  through  an  obstacle 
cither  solid  or  liquid,  when  partially  or  totally  reflected,  &c.;  not  merely  in  a 
scientific,  but  also  in  a  practical  point  of  view,  since  the  object  of  every  science 
ought  to  be  its  application?  Is  it  not,  in  fact,  desirable  that  the  spectacle  so 
humiliating  to  science  should  cease,  of  all  the  fruitless  or  ridiculous  efforts 
made  in  architecture  every  day  to  remedy  acoustic  defects  which  could  neither 
be  avoided  nor  foreseen?  Is  it  not  deplorable  to  witness  that  in  Europe  there 
does  not  exist  a  passable  parliamentary  chamber  or  hall  of  audience  that  is 
not  due  to  hazard?  Let  it  be  distinctly  understood,  it  is  not  the  ignorance  of 
the  architects  that  I  accuse;  they  may  well  be  allowed  to  be  ignorant  of  what 
philosophers  do  not  suspect.  Neither  shall  I  reproach  musicians  with  heaping 
together  a  mass  of  artists  in  a  concert-room,  with  whose  acoustic  properties 
they  are  unacquainted,  with  a  view  of  annihilating  by  a  volume  of  sound,  which 
they  cannot  obtain,  the  defects  they  presume  to  exist  in  a  room  built  at  hazard; 
no,  they  are  sufficiently  unhappy  in  being  obliged  to  hear  to  the  end  the  cha¬ 
rivari  they  endeavour  to  render  harmonious. 

The  savants  are  the  persons  responsible  for  the  greater  number  of  these 
errors,  for  Art  expec»s  to  derive  all  her  light  from  Science.  Therefore,  it  is 
to  them  I  address  myself  to  support  a  petition,  which  I  do  not  make  (for  I 
never  make  any),  but  which  I  think  would  be  favourably  received  by  thegovern- 

34 — 2 


532 


ACOUSTICS. 


ment,  if  it  were  presented  and  supported  by  the  eminent  professors  of  physics 
by  whom  France  is  honoured. 

Project  of  Study  concerning  the  Acoustics  of  Public  Buildings. 

The  means  I  propose  (unless  better  be  offered)  to  endeavour  to  resolve  the 
questions  of  acoustics  concerning  public  buildings,  as  well  as  many  others 
which  at  the  present  day  check  the  advance  of  science,  consists  in  constructing, 
in  a  locality  properly  chosen,  a  deaf-and-dumb  room,  where  no  sound  could 
penetrate  without  the  will  of  the  experimenter,  and  whose  walls  should  be  at 
first  covered  internally  in  such  a  manner  as  to  reflect  no  sound.  If  it  were 
possible  to  satisfy  this  condition,  which  appears  to  me  not  to  be  doubted,  it  is 
evident  that  this  chamber  would  possess  no  sonority,  since  the  enclosed  air 
would  vibrate  as  it  would  in  unlimited  space,  and  consequently  only  act  as  a 
vehicle  of  sound.  There,  exempt  from  all  noise,  from  all  reflection,  in  a  word, 
from  all  disturbing  causes,  whatever  was  heard  would  be  understood. 

Passing  on  to  researches  concerning  the  transmission  and  reflection  of 
sound  in  a  limited  space,  we  should  at  first  assure  ourselves  that  no  node  of 
vibration  exists  in  the  room  thus  prepared,  at  least  to  any  sensible  degree. 
Then,  stripping  the  covering  from  the  ceiling,  which  I  suppose  flat,  for  the 
purpose  of  obtaining  a  reflecting  plane,  we  should  seek  in  the  air  the  position 
of  the  nodes  of  vibration,  to  which  various  sounds  produced  in  different  parts 
of  the  room  might  give  rise,  and  we  should  observe,  as  we  advanced,  that 
sound  is  carried  farther  with  the  reflecting  ceiling  than  it  was  in  the  first 
instance.  We  should  afterwards  uncover  the  floor  and  the  four  walls  in  suc¬ 
cession,  observing  at  each  new  modification  the  nodes  of  vibration  produced 
in  the  air  by  the  same  sounds  proceeding  from  the  same  places,  and  noting 
carefully  the  state  of  things  at  the  moment  the  sound  begins  to  lose  its  purity, 
that  is  to  say,  the  moment  the  sound  begins  to  remain  in  space  after  the  cessa¬ 
tion  of  the  cause  which  produced  it ;  for  that  a  sound  may  be  distinct,  it  is  not 
enough  that  it  appear  intense;  it  must  above  all  be  clear,  especially  in  speaking. 

We  should  next  replace  everything  as  at  first,  except  the  ceiling,  which 
should  remain  uncovered,  and  be  lowered  by  one-half  its  original  height  (that 
is  to  say,  we  should  have  a  temporary  ceiling  constructed,  which  would  only 
require  a  moderate  solidity) ;  then  we  should  remark,  in  the  first  place,  that  at 
equal  distances  the  same  sounds  appear  clearer  and  more  distinct  than  when 
the  ceiling  was  more  elevated,  as  we  ought  to  expect,  since  the  reflected  sound 
traverses  a  shorter  distance,  from  the  angle  of  incidence  being  greater,  and 
for  the  same  reason  the  reflection  is  more  complete.  We  should  afterwards 
repeat  the  experiments  in  analogous  cases  for  the  determination  of  the  nodes 
of  vibration;  then  we  should  again  uncover  the  floor  and  walls  successively 
and  in  the  same  order  as  before,  and  repeat  at  every  change  the  series  of  ex¬ 
periments  we  had  already  made  under  similar  circumstances. 

There  is  no  doubt  that  after  this  first  investigation  we  should  become  per¬ 
fectly  acquainted  with  all  the  acoustic  properties  connected  with  a  regular 
prismatic  space,  having  sides  of  an  infinite  resistance,  at  least  for  sounds  whose 
intensity  and  whose  extent  of  sonorous  wave  do  not  exceed  that  of  the  human 
voice. 

Let  there  be  now  constructed  within  this  chamber  a  second  chamber,  with 
slender  sides  about  half  a  yard  distant  from  the  walls  of  the  first,  in  order  to 
isolate  it  completely,  and  to  permit  a  free  circulation  of  the  air  between  the 
sides  of  the  two  chambers  for  the  experiments  to  be  made  there. 


ACOUSTICS  OF  PUBLIC  BUILDINGS. 


533 


Let  us  recommence  in  this  new  chamber,  where  the  reflections  will  be  only 
partial  and  confused,  the  series  of  experiments  made  already  in  the  other,  noting 
the  length  of  the  sonorous  wave  and  the  intensity  that  the  sound  has  when  it 
ceases  to  possess  all  the  clearness  we  may  desire,  as  also  the  influence  that 
re-covering  the  walls  of  the  first  chamber  may  exercise  on  the  second,  and, 
in  a  word,  all  the  observations  that  such  a  situation  would  give  us  an  oppor¬ 
tunity  of  making. 

After  this  second  operation,  there  would  remain  for  us  to  study  carefully  the 
influence  that  might  be  exerted  on  the  acoustic  state  of  the  room  by  currents 
of  cold  or  heated  air,  or  by  air  in  a  dry  or  moist  state,  proceeding  from  any 
particular  part  of  the  room;  also  the  influence  of  •apertures,  their  situation, 
the  nature  and  resistance  of  their  enclosing  sides,  and,  finally,  of  the  furniture, 
<X:c.  Hut  the  greater  portion  of  these  investigations  could  be  made  almost 
everywhere,  and  at  a  trifling  expense,  since  we  should  possess  certain  data, 
which  would  enable  us  always  to  say,  “  If  such  a  room  had  not  apertures,  it 
would  be  so  and  so ;  if  such  another  was  furnished,  it  would  be  so  and  so,”  &c. 

I  shall  probably  regret  not  having  entered  more  into  detail— not  to  have 
mentioned  a  number  of  experiments  to  be  made  on  reflection,  produced  under 
different  incidences  by  rough  or  polished  surfaces — to  have  said  nothing  of  the 
relation  which  should  exist  between  the  resistance  of  the  reflecting  plane  and 
the  length  of  the  sonorous  wave— and,  finally,  not  to  have  given  sufficient 
development  to  my  idea  of  making  felt  all  the  importance  of  my  proposal, 
both  in  a  scientific  and  practical  point  of  view.  Perhaps  I  shall  even  have 
to  regret  not  having  said  enough  to  render  my  meaning  perfectly  clear ;  but  I 
have  already  advanced  far  beyond  my  subject. 

Here  M.  Marloye  concludes  his  very  original  and  important  remarks,  which 
he  modestly  hints  are  lengthy,  but  necessary,  because  all  other  acoustic  and 
musical  experiments  and  instruments  are  useless  without  the  exquisite  organ 
of  hearing. 

If  it  be  once  clearly  established  in  the  mind  that 
sound  is  produced  by  the  vibration  of  the  air,  it 
would  be  expected  that  in  the  absence  of  this  me¬ 
dium  no  sound  could  be  obtained;  hence  the  sim¬ 
ple  experiment  of  placing  a  bell  (with  certain  pre¬ 
cautions  to  check  the  conduction  of  sound  by  solid 
conductors)  in  a  vacuum. 

With  the  exception  of  a  very  few  tremblings, 
which  will  find  their  way  (leak  out,  as  it  were) 
through  the  points  of  suspension  of  the  bell,  the 
sound  is  entirely  destroyed  by  the  removal  of  the 
air  from  the  interior  of  the  spherical  glass  vessel. 

It  is  evident  that  musical  and  all  sound-pro¬ 
ducing  instruments,  and  the  vocal  organs,  must 
be  surrounded  with  common  air  or  other  gaseous 
matter. 

Hydrogen  gas  presents  a  remarkable  feature  in 
this  respect,  as  it  entirely  alters  the  sound  of  a  bell 
enveloped  with  it ;  in  fact,  it  renders  the  bell  sound¬ 
less,  and  merely  records  the  thumps  of  the  clapper, 
and  even  this  might  be  prevented  by  placing  the 
bell  apparatus  (such  as  that  used  by  the  telegraph 


Fig.  436. 

The  Bell  shaken  or  rung 
in  a  spherical  Glass  ex¬ 
hausted  of  Aix. 


534 


ACOUSTICS. 


companies)  on  a  bad  conductor  of  sound.  It  is  usual  to  account  for  this 
almost  magical  effect  on  the  sound  of  the  bell  by  the  lightness  of  hydrogen 
gas.  No  doubt  this  has  a  great  deal  to  do  with  it;  but  there  are  vibratory 
powers  which  will  affect  this  gas,  and  cause  it  to  emit  the  most  piercing  notes. 
We  have  a  proof  of  that  in  the  vocal  organs ;  for,  when  a  small  quantity  of 
hydrogen  is  inhaled,  the  pitch  of  the  voice  is  raised  in  the  most  ridiculous 
manner —sopranos  fairly  screech,  and  as  to  bass  voices,  they  become  sadly 
depraved  and  degraded  into  the  thin  treble  of  senility.  Thus  it  would  appear 
that  as  the  exquisite  particles  of  ether  require  a  vibratory  power  of  millions  of 
'millions  of  movements  to  occur  in  a  second,  so  reason  would  suggest  that,  as 
hydrogen  is  the  lightest  known  form  of  matter,  there  are  few  musical  instru¬ 
ments,  except  the  vocal  organs,  wind  instruments,  and  organ-pipes,  that  can 
set  up  vibrations  which  will  communicate  themselves  to  tnis  gas.  A  regular 
series  of  experiments  with  every  kind  of  musical  instrument  caused  to  play 
by  or  in  hydrogen  gas  may  determine  this  question,  and  the  writer  proposes 
to  try  them,  and  will  report  the  results  in  due  time. 

Every  musical  instrument  is  accompanied  with,  and  does  set  up,  a  tremulous 
motion  felt  in  an  orchestra  on  the  backs  of  the  seats  against  which  the  singers 
may  be  leaning. 

These  impulses  set  up  waves  in  the  air,  just  as  a  constant  series  of  blows 
delivered  from  a  brass  ball  upon  the  surface  of  smooth  water  produces  waves. 

Sir  C.  Wheatstone’s  wave  apparatus  admirably  demonstrates  the  mechanism 
of  those  regular  disturbances  of  the  air  which  resolve  themselves  into  waves. 


F IG.  437. —  Wheatstone's  Wave  A pparatus. 


The  beads  attached  to  the  wires  can  only  move  in  a  vertical  plane,  and  yet, 
by  thrusting  under  them  sliders  of  wood  cut  in  the  form  of  waves,  the  spec¬ 
tator  has  suggested  to  him  the  idea  that  they  are  moving  bodily  from  one  end 
of  the  framework  to  the  other. 

There  is  no  test  so  delicate  or  so  well  adapted  to  show  the  transmission  of 
vibrations  and  physical  disturbances  of  the  air  as  certain  flames,  such  as 
those  used  in  the  experiments  of  Mr.  W.  F.  Barrett. 

“  Three  years  ago  *  (December,  1865),  whilst  engaged  in  some  acoustic  ex¬ 
periments,  this  gentleman  observed  that  every  time  a  shrill  note  was  produced 
a  tall,  tapering  gas-flame  in  his  vicinity  was  singularly  affected,  the  flame 
shrinking  every  time  the  note  was  sounded.  That  observation  led  to  further 
experiment  and  inquiry,  the  result  of  which  has  been”  the  discovery  of  the 
conditions  of  success  for  obtaining  flames  sensitive  to  the  slightest  sound. 


*  Lecture  delivered  before  the  Dublin  Royal  Society  by  Mr.  W.  F.  Barrett.  “  Chemical  News,  ’ May  8, 1868. 


WAVES  OF  SOUND. 


535 


Some  months  after  the  above  observation,  Professor  Tyndall  took  up  the  sub¬ 
ject,  and,  having  largely  added  to  its  interest  and  importance,  offered  an  ex¬ 
planation  of  the  phenomenon  in  a  lecture  delivered  at  the  Royal  Institution, 
in  January,  1867.  At  this  lecture  the  discovery  was  first  published,  and  the 
name  given  to  ‘  Sensitive  Flames.’  Subsequently  Mr.  Barrett  proposed  a 
fuller  explanation,  and  discovered  that  not  only  flames,  but  all  gases,  could  be 
rendered  extremely  sensitive  to  sound — the  track  of  the  gas  being  marked  by 
mixing  it  with  smoke.*  This  historical  notice  would  be  unjust  without  refer¬ 
ring  to  an  observation  made  ten  years  ago  in  America  by  Professor  Leconte. 
That  physicist  had  noticed  that  certain  sustained  sounds  in  an  instrumental 
concert  caused  a  very  perceptible  movement  of  the  ordinary  gas-flames  in  the 
room.  This  observation  is  really  the  germ  of  the  more  wonderful  effects  after¬ 
wards  independently  discovered  by  the  lecturer.  Though  Professor  Leconte 
was  the  first  to  publish  the  fact  in  1858,  it  appears  that,  previous  to  this  date, 
artisans  had  frequently  noticed  the  phenomenon  as  resulting  from  the  shrill 
sounds  of  their  work;  and  several  musicians  have  informed  the  lecturer  that 
the  same  effect  has  been  one  they  have  commonly  observed. 

“  Turning  now  from  scientific  history  to  experiment,  the  lecturer  showed 
various  kinds  and  degrees  of  sensitive  flames.  First,  a  ‘batswing’  flame, 
which,  under  the  ordinary  gas  pressure,  moved  slightly  at  the  sound  of  a 
whistle,  but  thrust  out  long  tongues  of  fire  when  the  pressure  was  increased 
by  urging  the  gas  from  a  holder.  This  increased  pressure  was  always  neces¬ 
sary  to  obtain  the  more  sensitive  flames,  for  a  reason  that  will  be  understood 
directly.  A  jet  of  gas,  issuing  from  a  V-shaped  orifice,  was  shown  to  be  quite 
insensible  to  sound  until  the  flame  reached  a  height  of  10  or  12  inches,  and 
then,  at  the  sound  of  certain  high  notes,  the  flame  shortened  and  spread  out 
into  a  fan-shape.  Whistling  to  this  flame  in  one  key  had  no  effect,  while  in 
another  the  effect  was  very  marked.  Playing  an  air  upon  a  so-called  bird-organ, 
the  flame  selected  the  high  notes,  and  promptly  shortened  at  their  recurrence. 

“  The  probable  cause  of  the  sensitiveness  of  these  flames  was  then  alluded 
to.  The  impact  of  air  evidently  had  nothing  to  do  with  the  phenomenon. 
This  was  strikingly  shown  in  the  following  experiment:  By  tapping  a  mem¬ 
brane  stretched  over  the  mouth  of  a  large  tin  funnel,  a  puff  of  air  could  be 
driven  with  such  force  from  the  narrow  extremity  that  a  candle  was  easily  ex¬ 
tinguished  some  12  ft  away.  Directing  this  puff  of  air  against  the  sensitive 
flame,  it  was  seen  that  the  flame  moved  violently,  but  was  utterly  unaffected 
when  the  puff  was  driven  either  to  the  right  or  left.  This  should  also  be  the 
case  if  in  former  experiments  it  were  the  impact  of  the  air,  and  not  the  sound, 
that  produced  the  effect.  But  it  was  at  once  seen  that  when  the  lecturer 
whistled,  at  the  same  time  slowly  turning  round,  the  flame  still  continued  to 
shrink,  and  was  almost  as  powerfully  moved  when  the  back  was  turned  to  the 
flame.  The  effect,  then,  is  solely  produced  by  the  wave-like  to-and-fro  motion 
of  the  sonorous  pulses.  As  first  indicated  by  Professor  Leconte,  a  gas-flame 
to  be  sensitive  has  to  be  brought  near  its  point  of  roaring;  it  then  stands, 
according  to  Dr.  Tyndall,  as  it  were  on  the  brink  of  a  precipice,  over  which 
the  sound  pushes  it.  Agreeing  with  this  explanation,  that  a  sensitive  flame  is 
a  body  in  a  state  of  unstable  equilibrium,  the  lecturer  supplemented  it  by 
comparing  the  flame  to  a  resonant  jar,  the  flame,  as  was  proved  by  a  moving 
mirror,  being  in  a  state  of  rapid  isochronous  vibration  when  under  the  influ- 


”  “  Philosophical  Magazine,”  March  and  April,  1867. 


536 


ACOUSTICS. 


ence  of  external  sound.  The  actual  shrinking  of  the  flame  was  due  to  an 
increase  in  the  velocity  of  the  current  of  gas,  which  was  possibly  brought 
about  by  an  external  sound  throwing  the  pipe  that  conveys  the  gas  into  a  state 
of  vibration,  which  would  thus  narrow  the  channel  of  the  gas  passage — the 
change  in  the  aspect  of  the  flame  being  largely  modified  by  the  shape  of  the 
burner.” 

At  the  Polytechnic,  it  was  shown  by  the  writer  that  the  clanking  of  a  chain 
in  the  gallery  of  the  lecture-room  affected,  at  a  distance  of  50  ft.,  the  sensitive 
flame  burning  from  a  jet  made  of  glass  tube  £  of  an  inch  in  diameter,  and 
drawn  out  to  a  point  by  the  glass-blower  of  the  Institution. 

The  writer  obtained  nine  or  ten  glass  jets  that  answer  the  purpose  remark¬ 
ably  well ;  but  the  pressure  of  the  gas  burnt  must  be  high,  that  used  being 
equal  to  2  ft.  of  water,  or  about  1  lb.  on  the  square  inch. 

The  sensitive  flame  alluded  to  was  wholly  insensible  to  the  musical  notes  of 
a  fine  concertina,  the  lowest  and  highest  notes  of  the  syren,  the  shaking  of  an 
iron  plate,  as  in  the  production  of  artificial  thunder,  the  notes  of  a  violin  ;  but 
was  affected  to  a  ceitain  extent  by  the  notes  emitted  from  a  series  of  steel 
rods  cf  different  lengths,  struck  as  the  street  boys  strike  the  iron  railings 
with  a  piece  of  wood. 

The  writer  considers  that  the  effect  is  simply  that  of  “  a  resolution  of 
forces,”  in  which  the  motions  of  the  flame  are  affected  by  the  kindred  vibra¬ 
tions  of  certain  vocal  sounds  and  noises,  with  which  they  unite,  the  result 
being  no  longer  a  thin  perpendicular  line,  but  a  rude  approach  to  a  circular 
figure  when  perfectly  harmonious  or  in  unison,  or  other  curious  forms  accord¬ 
ing  to  the  nature  of  the  combined  movements  of  the  flame  and  the  air  set  in 
motion  by  the  vocal  organs,  or  by  any  noise,  such  as  the  rattling  of  keys.  It 
wculd  appear  from  the  syren  experiment  that  the  vibrations  which  affect  the 
flame  must  not  occur  too  rapidly. 

The  shape  of  the  flame  produced  by  two  jets  of  gas  crossing  each  other,  as 
in  the  fish-tail  burner,  is  the  resultant  of  two  opposing  currents  of  gas. 

If  one  gas  flame  can  affect  another,  and  alter  its  form,  it  is  easily  conceived 
that  any  impulse  of  air,  instead  of  burning  gas,  would  give  the  same  result 
as  in  the  sensitive  flames. 

Any  noise  repeated  a  given  number  of  times  will  have  a  proper  musical 
value.  A  crack,  a  snap,  a  bounce,  a  crash,  an  explosion,  a  rumbling,  may  be 
classed  together  as  noises ;  and  yet  it  will  be  found  that  it  is  quite  possible  to 
demonstrate  that  some  of  these  noises  may  be  converted  by  constant  repeti¬ 
tion  into  true  musical  sounds. 

Mr.  Pichler  made  for  the  writer  an  enlarged  syren,  having  six  large  holes, 
alternately  opened  and  shut  by  a  revolving  plate  with  six  apertures,  provided 
with  lean-to  roofs,  like  those  placed  .over  the  cabin  stairs  of  steam  or  other 

vessels. 

When  this  contrivance  is  connected  with  powerful  bellows,  the  first  noise 
heard  is  that  of  a  rushing  wind,  alternately  escaping  and  cut  off;  and  as  the 
velocity  of  the  revolving  plate  is  gradually  raised,  the  noise  is  changed  to  a 
series  of  musical  sounds,  rising  in  the  scale  according  to  the  force  used  to 
impel  the  air  through  the  apparatus. 

The  ordinary  syren,  invented  by  Cagniard  Latour,  and  so  called  because  (like 
the  sea-nymphs  who  charmed  with  their  songs  all  who  came  near  them)  it  is 
erroneously  supposed  to  give  sounds  under  water,  consists  of  a  lower  plate,  form¬ 
ing  the  top  cf  a  circular  box,  which  is  perforated  with,  say,  ten  slanting  holes  at 


THE  SYREN. 


537 


equal  distances;  above  this  plate  another  revolves,  also  perforated  with  a  similar 
number  of  apertures,  not  bored  perpendicular  to  the  axis,  but  inclined  in  the 
opposite  direction  to  those  in  the  lower  plate,  so  that  when  one  aperture  is  over 
the  other,  a  zigzag  figure  is  the  result.  The  upper  plate  carries  a  shaft  or  axis 
which  has  an  endless  screw  at  the  top ;  and  as  this  revolves  by  the  force  of  the 
wind  escaping  from  the  bellows,  it  transmits  the  motion  to  a  wheel  with  one 
hundred  teeth,  and  every  time  the  latter  goes  round  once  the  one  hundred 
revolutions  are  recorded  on  another  wheel;  and  as  both  are  provided  with 


Fig.  438. —  The  enlarged  Syren , 

For  producing  a  “puff,  puff”  noise,  similar 
lo  that  of  a  locomotive. 


Fig.  439. —  The  Syren  and  Bellows. 


needles,  which  move  over  numbered  dials,  like  those  of  a  gas  meter,  the  exact 
number  of  revolutions  per  second  can  be  determined.  The  sound  gradually 
rises  as  the  velocity  is  increased,  until  the  syren  fairly  screams,  and  emits  such 
piercing  cries  that,  had  the  ancient  ladies  called  syrens  performed  in  a  similar 
manner,  it  is  easy  to  understand  why  Ulysses  stuffed  his  ears  with  wax  and 
tied  himself  to  the  mast  of  his  vessel  to  avoid  the  dangerous  effects  of  their 
vocal  powers,  which  might,  like  some  of  the  modern  street-singers,  have  driven 
him  mad  and  overboard,  to  escape  from  the  excruciating  torment. 

Supposing  the  syren  to  be  urged  with  the  bellows  until  the  deepest  note  of 
the  bass,  viz.,  Ct,  do,  is  obtained.  If  this  be  continued  for  two  minutes,  or 
120  seconds,  the  dial  would  record  1,536  revolutions;  but  the  revolving  disc 


538 


ACOUSTICS. 


has  ten  holes,  then  1,536x10=15,360,  which,  divided  by  120,  gives  128  vibra¬ 
tions  per  second  for  the  note  C„  or  that  which  is  called  do.  The  syren  is, 
therefore,  extremely  valuable,  as  it  shows  the  number  of  impulses  per  second 
required  to  produce  any  given  sound;  and  thus  it  is  found  by  actual  experi¬ 
ment  that  the  seven  notes  of  the  gamut,  commencing  with  the  deepest  note 
of  the  bass,  are  as  follows : 


Ci 

Do 

1 28  vibrations 

per  second 

D, 

Re 

144 

ff 

ff 

E, 

Mi 

160 

ff 

ff 

F, 

Fa 

170 

ff 

ff 

G, 

Sol 

192 

r> 

If 

A, 

La 

214 

ff 

ff 

B, 

Si 

240 

ff 

ff 

The  notes  of  other  and  higher  scales  would  start  with  an  index  C2  or  C3,  &c.; 
whilst  those  of  a  lower  scale  would  be  designated  as  - — I,  — 2,  — 3,  &c. 

These  figures  have  a  constant  relation  to  the  length  of  the  wave  of  sound 
to  which  they  refer — a  fact  easily  determined  by  the  monochord  already  alluded 
to  (p.  485,  Fig.  435). 

The  last-named  apparatus  consists  of  a  string  or  wire  stretched  by  weights 
or  a  screw  (as  in  an  ordinary  violin)  across  two  bridges,  one  at  each  end; 
there  is  also  a  movable  bridge,  and,  supposing  this  to  be  placed  at  a  distance 
equal  to  a  third  of  the  whole  length,  and  then  vibrated  by  drawing  a  bow  over 
it,  the  string  divides  itself  into  three  parts,  each  of  which  has  its  own  vibra¬ 
tion  or  wave-like  figure. 

Between  these  parts  there  are  points  where  the  motion  is  almost  nil  or  o, 
called  nodal  or  fixed  points,  whilst  the  part  of  the  string  vibrating  between 
two  fixed  points  is  called  the  ventral  segment. 

This  fact  is  proved  by  placing  pieces  of  paper,  cut  like  an  inverted  V,  on 
the  above-named  parts,  which  remain  as  riders  firmly  seated  at  the  nodal 
points,  but  are  thrown  off  at  the  ventral  segments. 

The  plates  on  which  are  produced,  by  vibration,  the  figures  called  Chladni’s 
sand-figures  (p.  474,  Fig.  433)  and  membranes,  present  the  same  feature,  and 
have  points  of  rest  (nodal  points)  where  the  sand  collects  to  produce  the  figure, 
and  other  parts  from  which  the  sand  is  set  into  vibration  and  shaken  off. 

The  musical  scale  or  gamut — so  called,  it  is  said,  because  the  inventor, 
Guido,  of  Arezzo,  improved  upon  the  ancient  Grecian  scale,  and,  in  acknow¬ 
ledgment  of  its  origin,  called  his  scale  from  the  Greek  letter  Gamma — the 
gamut  consists  of  seven  notes  separated  from  each  other  by  intervals,  and,  if 
repeated,  again  reproduced  in  periods  of  seven  each,  called  a  scale  or  gamut. 

Each  scale  has  waves  of  different  lengths,  that  can  be  estimated  by  numbers. 
Taking  the  velocity  of  sound  as  equal  to  1,024  ft.  per  second,  if  we  imagine  a 
string  of  that  length  vibrating  once  in  that  period  of  time,  the  length  of  the 
wave  would  be  1,024  ft-!  if  it  made  three  vibrations  in  the  same  period,  the 
length  would  be  1,024-^3  =  341-333. 

It  has  been  observed  that  the  deepest  bass  note,  Ci,  is  equal  to  128  vibrations 
per  second;  therefore,  1,024-^-128  =  8  ft.,  i.e.,  a  note,  C„  is  produced  by  128 
vibrations  or  waves,  each  of  which  is  8  ft.  in  length. 

If  a  lower  sound  than  C,  is  produced,  viz.,  C_i,  or  16  vibrations  per  second, 
the  length  of  each  wave  is  64  ft.  When  the  sound  is  equal  to  1,024  vibrations 
per  second,  or  C.,  the  length  of  each  wave  is  1  ft. 


THE  SYREN. 


539 


Having  the  two  extremes,  the  lowest  appreciable  sound,  consisting  of  16 
vibrations  per  second,  C_i,  and  the  highest,  C4,  or  1,024  Per  second,  it  is  easy 
to  work  out  a  table  of  the  length  of  the  waves  of  the  intermediate  scales  cor¬ 
responding  to  the  first  note  of  the  successive  gamuts. 

Savart  considered  that  the  lowest  sound  the  human  ear  could  appreciate 
consisted  of  from  14  to  16  vibrations,  and  the  highest  of  48,000  vibrations,  per 
second. 

Dcspretz,  whose  name  is  mentioned  by  Marloye  as  the  physicist  for  whom 
he  made  the  tuning-forks,  considered  that  32  vibrations  and  73,700  per  second 
represented  the  deepest  and  most  acute  sounds  appreciable  by  the  auditory 

nerve. 

Dr.  Wollaston  stated  that  we  are  sensible  of  vibratory  motion  until  it  be¬ 
comes  a  mere  tremor,  which  may  be  felt  and  even  almost  counted. 

A  sound  may  be  so  shrill  that,  though  audible  to  one  person,  it  may  not  be 
heard  by  another. 

Wollaston  mentioned  the  case  of  a  friend  of  his,  whose  power  of  hearing, 
though  excellent,  did  not  permit  him  to  appreciate  the  chirping  of  the  house- 

sparrow. 

The  same  great  philosopher  remarks  that 

“The  suddenness  of  transition  from  perfect  hearing  to  total  want  of  percep¬ 
tion  occasions  a  degree  of  surprise,  which  renders  an  experiment  on  this  sub¬ 
ject,  with  a  series  of  small  pipes,  among  several  persons,  rather  amusing. 

“A  pipe,  one-fourth  of  an  inch  in  length,  produced  a  sound  supposed  to  be 
about  six  octaves  above  the  middle  F  (which  was  the  limit  of  his  own  hearing); 
but  some  persons  could  not  hear  that,  and  others  could  hear  higher.  The 
whole  range  of  human  hearing,  between  the  lowest  notes  of  the  organ  and 
the  highest  of  insects  audible  to  man,  is  supposed  to  be  about  nine  octaves ; 
and,  although  some  individuals  can  hear  sounds  not  audible  to  others,  there 
is  at  least  but  little  difference  in  the  range  of  human  hearing,  although  the 
existence  of  a  limit  cannot  be  disputed.” 

Professor  Galton  has  invented  a  novel  form  of  whistle,  which  can  be  ob¬ 
tained  from  Messrs.  Tisley,  172  Brompton  Road,  London.  By  means  of  a 
fine  screw  with  a  milled  head,  the  sound  emitted  may  be  made  so  shrill  that 
it  can  be  used  as  a  test  of  the  delicacy  of  hearing  ;  so,  that  starting  with  half 
a  dozen  persons,  it  is  soon  found  that  the  limit  of  hearing  is  reached  with  the 
greater  number,  who  are  obliged  to  confess  they  cannot  hear  sounds  which 
perhaps  only  one  person  out  of  that  number  can  appreciate. 

Before  dismissing  the  syren,  it  is  of  importance  to  speak  of  a  simple  form 
of  this  instrument,  first  devised  in  Paris,  and  now  made  by  Mr.  Ladd. 

A  disc,  perforated  with  holes  in  regular  and  irregular  intervals,  is  turned 
round  fast  or  slow,  and  whilst  revolving  a  strong  blast  of  air  is  blown  through 
the  holes  by  the  mouth  with  a  flexible  tube  and  ivory  mouthpiece  and  jet.  It 
is  very  interesting  to  mark  the  rise  of  the  notes  produced  as  the  velocity  of 
the  holes  increases  or  decreases,  discoverable  by  moving  the  jet  from  the  cir¬ 
cumference  to  the  centre.  The  following  description  of  the  number  and 
arrangement  of  the  perforations  is  furnished  with  the  instrument: 

“The  disc  is  perforated  with  1,682  holes,  apportioned  into  twenty-four  con¬ 
centric  circles,  the  fifteen  interior  ones  being  divided  into  regular,  and  the 
remainder  into  irregular,  intervals.  The  former  are  divided  in  the  following 
proportions:  For  every  two  holes  in  the  first  circle  (counting  from  the  centre) 
there  are  three  in  the  second,  four  in  the  third,  five  in  the  fourth,  six  in  the 


ACOUSTICS. 


F IG  440. — New  Form  of  Syren ,  made  by  Ladd. 


fifth,  eight  in  the  sixth, 
ten  in  the  seventh,  twelve 
in  the  eighth,  sixteen  in 
the  ninth,  twenty  in  the 
tenth,  twenty-four  in  the 
eleventh,  thirty-two  in  the 
twelfth,  forty  in  the  thir¬ 
teenth,  forty-eight  in  the 
fourteenth,  and  sixty-four 
in  the  fifteenth.  If  with  a 
small  tube  you  blow  into 
these  circles  whilst  the 
disc  is  in  rapid  rotation,  a 
series  of  musical  notes  will 
be  obtained,  allied  to  each 
other  in  the  relative  pro¬ 
portion  of  the  numbers, 
booking  at  the  outer  por¬ 
tion  of  the  disc,  lines  of 
holes  are  observed  radiat¬ 
ing  from  the  centre,  and 
dividing  the  disc  into  24 
equal  parts ;  and,  if  the 
other  holes  were  stopped, 

each  of  these  rings  would  produce  a  single  sound  the  same  as  the  sixth  row 
of  the  inner  series.  This  note  will  form  the  fundamental  of  all  the  harmonics. 
If  we  take  a  po;nt  in  the  first  of  the  external  rings,  and,  starting  from  it,  with 
a  pair  of  compasses  repeat  the  distance  between  it  and  the  first  intermediate 
hole  five  times,  it  will  correspond  with  four  of  the  fundamental  spaces;  and  if 
a  single  jet  of  air  be  forced  through  these  holes  whilst  the  disc  is  rotating,  the 
idea  conveyed  to  the  mind  will  be  precisely  the  same  as  if  two  separate  notes 
were  sounded  together — the  two  notes  being  a  fundamental  and  its  third,  the 
proportions  of  the  vibrations  being  as  5  :  4.  The  second  rew  is  divided  in  the 
ratio  of  4  :  3 — this  will  give  a  fundamental  and  its  fourth  (or  sub-dominant) ; 
the  third  row  is  divided  as  3  :  2,  giving  the  fundamental  and  its  fifth  (or  domi¬ 
nant);  the  fourth  row,  divided  as  5  :  3,  gives  a  fundamental  and  its  sixth;  the 
fifth  row  is  as  7  :  4 — this  giving  a  fundamental  and  flat  seventh;  the  sixth  row 
has  a  combination  of  four  holes,  in  the  proportion  of  6  :  5  :  4  :  3 — this  will  give 
a  perfect  chord  of  four  notes;  the  seventh  row  has  four  holes,  in  the  propor¬ 
tion  of  8:6:5:  4 — this  will  give  a  perfect  chord  with  octave  of  the  funda- 
mental ;  the  eighth  row  is  divided  in  the  proportion  of  5  :  4  :  3,  giving  a  perfect 
major  triad  with  inverted  fifth;  and  the  last  row  is  divided  in  the  proportion 
6:5:4,  which  forms  a  perfect  major  triad.” 

The  conversion  of  noise  into  musical  sounds  is  shown  in  the  most  elegant 
manner  by  an  instrument  devised  by  Froment. 

A  small  electro-magnet,  with  a  break  fastened  at  one  end  in  the  ordinary 
way  to  one  pole  and  vibrating  on  the  other  pole,  is  connected  with  a  small 
battery ;  directly  contact  is  made,  the  break,  acting  like  a  tiny  hammer,  is 
attracted  so  frequently  to  the  other  pole,  which  it  strikes,  that  a  sound  like 
that  emitted  by  a  bluebottle  is  distinctly  audible,  rising  to  an  acute  sound  as 


FRO  ME  NTS  AREA  RATES. 


54i 


the  screw  is  moved,  which  regulates  the  distance  of  the  break  and  increases 
the  number  of  contacts  per  second.  Thus  a  hammering  noise  is  converted 
by  mere  repetition  into  a  musical  sound. 

Speaking  of  the  bluebottle  and  of  the  supposed  production  of  the  sound 
by  the  vibrations  of  its  wings,  a  friend  of  the  author  writes  as  follows  : 

“  I  have  read  of,  and  also  tried,  the  cruel  though  interesting  experiment  of 
taking  off  the  wings  of  flies,  bluebottles,  &c.,  and  have  noticed  that  sounds 
were  emitted  after  the  disappearance  of  the  wings.  How,  then,  can  this  be 
accounted  for,  if  the  sound  (as  stated  in  some  books)  be  produced  by  the 
vibratory  motion  of  the  wings  ?  And,  moreover,  we  read  in  other  byoks  on 
‘Acoustics’  of  a  peculiar  mechanism,  particularly  in  bluebottles  and  humble- 
bees,  through  which  the  rapid  transmission  of  air  causes  a  fibrous  thread¬ 
like  apparatus  to  vibrate,  thus  causing  the  peculiar  buzzing  sound  made  by 
those  insects.” 

On  the  principle  already  explained,  it  is  easy  to  understand  why  sounds  are 
obtained  by  burning  a  jet  of  hydrogen  inside  a  glass  tube.  This  curious  fact 
was  first  observed  by  Dr.  Higgins  in  the  year  1 777,  and  further  examined 
by  Brugnatelli,  Pictet,  De  la  Rive,  and  Faraday. 


Fig.  441. — FromenPs  Apparatus. 


The  latter  philosopher  considered  that  the  sounds  were  producible  by  the 
gas  not  burning  silently,  but  with  a  series  of  inaudible  explosions  in  the  open 
air,  rendered  audible  when  burnt  in  a  tube  by  the  resonance  of  the  tube,  a 
term  that  will  be  more  fully  explained  hereafter. 

It  is  not  every  glass  tube  that  will  resound  or  sympathize  with  the  explosions 
of  the  gas;  but,  generally  speaking,  it  is  easy  to  obtain  them,  and,  as  Mr. 
Barrett  remarked  in  his  lecture  given  before  the  Dublin  Royal  Society,  “  thus 
rough  and  rude  taps  and  hard  and  harsh  explosions  can  be  chased  into  per- 
iect  melody  by  mere  rapidity  of  succession. 

“The  condition  of  the  flame  when  burning  within  the  tube  is  shown  by  a 
moving  mirror.  It  was  seen  that  when  the  flame  was  silent  and  the  mirror 
moving,  a  band  of  light  was  produced ;  but  when  the  flame  was  sounding, 
this  luminous  ribbon  was  broken  up  into  a  series  of  disjointed  images  of 
flame.  The  effect  of  lengthening  the  lube  in  which  the  flame  was  burning 
was  next  shown,  and  a  series  of  gas  jets  burning  within  glass  tubes  of  varying 
length  gave  a  corresponding  series  of  musical  notes  of  varying  pitch.  By 
placing  the  firger  upon  the  top  of  these  tubes,  the  sound  could  be  quenched, 
and  thus  a  novel  musical  instrument  could  be  constructed.  From  glass  tubes 


542 


ACOUSTICS. 


the  lecturer  passed  on  to  show  the  ef- 
ects  of  flames  burning  within  extremely 
long  tin  tubes.  Within  a  tube  6  ft.  long 
and  about  in.  in  diameter,  the  flame 
of  a  large  gas-burner  gave  a  loud,  un¬ 
musical  roar.  By  adding  to  the  end  of 
this  tube  a  glass  chimney,  it  was  seen 
that  when  the  flame  was  sounding  it 
was  broken  up  into  wild  confusion.  By 
enciosipg  a  still  larger  gas-flame  from 
a  huge  Bunsen’s  burner  within  a  tube 
1 8  ft.  long  and  3  in.  in  diameter,  a  deep 
roar  was  obtained,  intermingled  with 
loud  reports  similar  to  the  discharge  of 
musketry. 

“  Returning  once  more  to  the  gentler 
music  of  the  small  glass  tubes,  two 
flames,  enclosed  in  their  respective 
tubes,  were  taken  and  made  to  emit 
notes  of  the  same  pitch.  This  point 
was  gained  by  shifting  to  and  fro  a 
paper  slider,  which  moved  stiffly  at  the 
upper  extremity  of  one  of  the  tubes. 
When  the  notes  were  nearly  in  unison 
a  series  of  intermittent  sounds  or  beats 
were  ODiained,  due,  as  is  well  known, 
to  the  mutual  extinction  at  certain  in¬ 
tervals  of  the  two  sounds.  Correspond¬ 
ing  beats  were  obtained  from  two  organ- 
pipes  and  two  tuning-forks  nearly  in 
unison.  One  of  these  tuning-forks, 
mounted  on  its  resonance  case,  being 
silent,  the  other,  unmounted,  was  now 
struck,  and  its  prongs  brought  near  to, 
but  not  touching,  those  of  the  first  fork: 
at  first  no  sound  could  be  heard,  but  by 
degrees  the  unmounted  fork  transferred 
its  motion  to  the  mounted  one,  and  the 
sound  of  the  latter  slowly  welled  forth. 
The  sound  of  the  voice  can  thus  be 
transferred  to  the  strings  of  a  piano¬ 
forte,  and  in  the  same  way  a  flame  can 
be  made  to  accept  and  resound  to  a 
note  of  the  proper  pitch.  This  was 
illustrated  as  follows:— A  singing  flame, 
by  adjusting  the  paper  slider,  was  tuned 
to  the  note  of  a  certain  fork  ;  the  tube 
was  then  raised  slightly,  ro  that  the 
sound  could  be  quenched  by  momen¬ 
tarily  placing  the  finger  on  the  top  of 
the  tube.  On  now  striking  the  fork,  and 


MUSICAL  FLAMES. 


543 


holding  it  over  a  resonant  jar,  the  flame  instantly  started  into  song.  The  same 
effect  was  shown  by  the  syren,  and  also  by  the  human  voice.  Retreating  to 
so  ne  distance  from  the  flame,  the  latter  could  be  made  to  respond  at  pleasure 
by  pitching  the  voice  to  the  proper  note,  whilst  it  remained  utterly  unaffected 
by  any  note  not  in  unison  with  itself.  Musicians  would  find  such  a  flame  a 
faithful  monitor  in  training  the  voices  of  their  pupils.” 

The  apparatus  used  by  the  writer  at  the  Polytechnic  is  shown  on  the  pre¬ 
ceding  page.  (Fig.  442.) 

Tne  organ-pipe  was  1 5  ft.  in  length,  and  emitted  a  fine  deep  sound  when  an 
Argand  burner  was  used,  whilst  with  a  large  Bunsen’s  burner  the  sound  rose 
with  the  increased  supply  of  gas  to  a  roaring  noise,  which  reminded  one  of 
the  vocal  powers  of  the  lion  at  the  Zoological  Gardens,  just  before  the  tanta¬ 
lizing  (to  him)  bits  of  raw  meat  are  served  for  his  dinner. 

The  beats  were  very  distinct;  and  on  one  occasion  the  writer  noticed  that, 
whilst  the  pipe  was  sounding,  the  heated  air  appeared  to  divide  itself  into  ven¬ 
tral  segments  a  id  nodal  points,  the  latter  being  apparently  discoverable  by 
the  increased  heat  where  the  hot  air  remained  at  rest,  as  at  the  nodal  points, 
whilst  the  cooler  parts  of  the  pipe  might  be  the  ventral  segments,  where 
agitation  mixed  the  air,  and  prevented  that  quiescence  which  would  give  time 
to  the  air  to  give  out  its  heat  to  the  sides  of  the  pipe ;  but,  curious  to  say,  this 
result  could  not  be  obtained  again,  and,  therefore,  the  absolute  proof  that  a 
column  of  heated  air  can  divide  itself  into  waves  emitting  a  greater  heat  at 
the  nodal  points  than  the  ventral  segments  remains  yet  to  be  obtained. 

Mr.  Becker,  of  Elliott’s,  who  constructed  the  organ-pipe  apparatus,  also 
arranged  for  the  writer  a  series  of  brass  tubes  increasing  in  length,  having 
inside  them  small  Bunsen  burners,  and  producing,  when  the  valves  fixed  to  the 
top  of  each  tube  were  lifted  by  strings  attached  to  a  key-board,  the  notes  of  the 
gamut.  (Fig.  443.) 

With  this  gas-flame  organ  Herr  Shalckenbach,  the  much-respected  organist 
of  the  Polytechnic,  could  play  simple  tunes,  to  the  great  admiration  and  de¬ 
light  of  the  youthful  spectators. 

It  has  already  been  remarked  that  the  gas-flames  do  not  give  out  or  produce 
sound,  except  they  arc  clothed  or  surrounded  with  a  tube  made  of  glass,  metal, 
or  any  other  convenient  substance.  The  curious  jumping  up  and  down  of  a 
single  flame  that  precedes  the  evolution  of  sound  has  been  ascribed  (as  already 
stated)  by  Faraday  to  a  series  of  explosions.  The  writer  is  inclined  to  doubt 
this  being  the  correct  explanation,  because  whenever  a  true  explosion  takes 
place,  the  flame  is  extinguished.  It  has  more  to  do  with  the  current  which  is 
constantly  dragging  the  flame  upwards,  and  the  fire  is  as  constantly  running 
downwards  to  the  jet :  here  are  a  series  of  impulses,  an  up-and-down  motion, 
or  vibratory  power,  sufficient  to  set  the  air  into  waves,  which  are  communicated 
by  contact  to  the  glass  tube,  and  this,  by  resonance,  produces  the  sound. 

If  an  Argand  burner  be  used,  the  flame  is  quite  different :  whilst  the  sound 
is  being  produced,  the  flame  overflows  the  outside  of  the  ring,  and,  burning  very 
blue,  shows  the  rapidity  of  the  current  of  air.  It  seems  to  be  beaten  downwards, 
as  if  one  current  of  air  passed  up  the  centre  of  the  Argand  tube,  and  another 
came  down  outside;  but  there  is  not  any  indication  of  an  explosion,  except 
when  the  interior  of  the  tube  is  corked  or  stopped,  and  then  the  flame  is  con¬ 
tinually  extinguished  by  explosions. 

When  tested  by  the  mirror,  the  streak  or  band  of  light  is  continuous  :  there 
are  no  breaks  as  with  the  single  flame  because  that  is  prevented  by  the  com- 


544 


ACOUSTICS. 


Fig.  443. —  The  Gas-flame  Organ. 


plete  combustion  of  the  gas;  there  is  no  jumping  up  and  down  and  intermit¬ 
tent  combustion, — it  is  continuous;  and  yet  sound  is  evoked.  The  ring  of 
burning  gas  is  violently  agitated  by  the  current  of  air  in  the  tube;  it  is  con¬ 
stantly  wishing  to  rise,  and  is  as  constantly  beaten  down  ;  thus  it  is  the  current 
of  air  that  determines  the  whole  effect,  and  there  are  no  explosions  whatever. 
If  one  really  occurs,  the  flame  is  blown  out,  as  might  be  expected.  It  is  pro¬ 
bably  intermittent  combustion  which  sets  the  air  vibrating. 

I  o  show  how  completely  the  sound  is  affecced  by  the  rate  or  rapidity  of  the 


FAR  ADA  Y'S  EXPERIMENTS. 


545 


current  of  air,  the  writer  used  a  single  jet  and  flame,  so  arranged  that  it  could 
be  bent  down  to  any  angle  to  the  perpendicular  with  the  tube  surrounding  it. 
The  flame  emitted  sound  at  an  angle  of  6o°,  but  every  degree  after  it  decreased, 
until  at  50°  it  stopped  and  refused  to  vibrate ;  and  when  the  tube  was  horizonal, 
the  flame,  as  might  be  expected,  stopped  singing  altogether,  and  clung  to  the 
upper  part  of  the  tube.  The  reader  will,  no  doubt,  be  interested  with  extracts 
from  Faraday’s  own  paper, 

“On  the  Sounds  produced  by  Flame  in  Tubes,  &c., 

“By  M.  Faraday,  Chemical  Assistant  in  the  Royal  Institution. 

“May  11,  1818* 

“  There  is  an  experiment  usually  made  in  illustration  of  the  properties  of 
hydrogen  gas,  which  was  first  described  by  Dr.  Higgins  in  1 777,  and  in  which 
the  tones  are  produced  by  burning  a  jet  of  hydrogen  within  a  glass  jar  or  tube. 
These  tones  vary  with  the  diameter,  the  thickness,  the  length,  and  the  sub¬ 
stance  of  the  tube  or  jar,  and  also  with  the  changes  of  the  jet.  After  Dr. 
Higgins,  Brugnatelli,  in  Italy,  and  Mr.  Pictet,  at  Geneva,  described  the  expe¬ 
riment.  and  the  effects  produced  by  varying  the  position  of  the  jet  and  tube  ; 
and  M.  de  la  Rive  read  a  paper  at  Geneva  in  which  he  accounted  for  the 
phenomena  by  the  alternate  expansion  and  contraction  of  the  aqueous  vapour. 
That  they  are  not  owing  to  aqueous  vapour,  from  some  experiments  to  be 
described,  I  have  no  doubt:  they  are  caused  by  vibrations  similar  to  those 
described  by  M.  de  la  Rive,  but  the  vibrations  are  produced  in  a  different 
manner,  and  may  result  from  the  action  of  any  flame.  1  was  induced  to  make 
a  few  experiments  on  this  subject.  That  the  sounds  were  not  owing  to  any 
action  of  aqueous  vapour  was  shown  by  heating  the  whole  tube  above  21 2°, 
and  still  more  evidently  by  an  experiment  in  which  I  succeeded  in  producing 
them  from  a  jet  of  colza  oil  gas.  That  they  do  not  originate  by  vibration  of  the 
tube,  caused  by  the  current  of  air  passing  through  it,  was  shown  by  using 
cracked  glass  tubes — tubes  wrapped  m  cloth  ;  and  I  have  obtained  very  fine 
sounds  by  using  a  tube  formed  at  the  moment  by  rolling  up  half  a  sheet  of 
cartridge  paper,  and  keeping  it  in  form  by  grasping  it  in  the  hand. 

“Sir  H.  Davy  has  explained  the  nature  of  flame  perfectly,  and  has  shown 
that  it  is  always  a  combination  of  the  elements  of  explosive  atmosphces.  In 
continued  flame,  as  of  a  jet  of  gas,  the  combination  takes  place  successively 
and  without  noise  as  the  explosive  mixture  is  made.  In  what  is  properly 
called  an  explosion,  the  combination  takes  place  at  once  throughout  a  con¬ 
siderable  quantity  of  mixti  re,  and  sound  results  from  the  mechanical  forces 
thus  suddenly  brought  into  action,  and  a  roaring  flame  presents  something  of 
the  appearance  of  both.  Dow,  this  I  believe  to  be  exactly  analogous  to  that 
which  takes  place  in  what  have  been  called  the  singing  tubes,  but  in  them 
the  explosions  are  generally  more  minute  and  more  rapid.  By  placing  the 
flame  in  the  tube,  a  strong  current  of  air  is  determined  up  it,  which  envelopes 
the  flame  on  every  side.  The  current  is  stronger  in  the  axis  of  the  tube  than 
in  any  other  part,  in  consequence  of  the  friction  at  the  sides  and  the  position 
of  the  flame  in  the  middle  and  just  at  the  entrance  of  the  tube.  An  additional 
effect  of  the  same  kind  is  produced  by  the  edge  obstructing  the  air  which 
passes  near  it.  The  air  is,  therefore,  propelled  on  to  the  flame,  and,  mingling 


*  “  Quarterly  Journal  of  Science,”  Vol  V. 


546 


ACOUSTICS. 


with  the  inflammable  matter  existing  there,  forms  portions  of  exploding  mix¬ 
tures,  which  are  fired  by  the  contiguous  burning  parts,  and  produce  sound  in 
the  manner  already  described  with  a  roaring  flame,  only  the  impelled  current 
being  more  uniform,  and  the  detonations  taking  place  more  regularly  and  in 
smaller  quantities,  the  sound  becomes  continuous  and  musical,  and  is  tendered 
still  more  so  by  the  effect  of  the  tube  in  forming  an  echo. 

“That  the  roaring  flame  gives  sound  in  consequence  of  explosions  can 
hardly  be  doubted. 

“  An  experiment  may  be  made  with  coal-gas.  Light  a  small  Argand  burner 
with  a  low  flame,  and  bring  a  glass  tube,  which  is  very  little  larger  than  the 
diameter  of  the  flame,  down  upon  it  so  as  nearly  to  include  it.  The  current 
of  air  will  be  impelled  upon  the  external  part  of  the  flame,  it  will  remove  the 
limit  of  combustion  a  little  way  up  from  the  burner,  that  part  of  the  flame 
will  vibrate  rapidly,  burning  with  continued  explosions,  and  an  irregular  tone 
will  be  obtained.  Remove  the  burner,  and  attach  a  long  slender  pipe  to  the 
gas-tube,  so  as  to  afford  a  candle-flame  that  may  be  introduced  into  the  tube. 
Light  it  and  introduce  it  about  five  or  six  inches,  and  a  clear  musical  tone 
will  be  obtained.” 


Fig.  444. — Savart's  Apparatus  for  showing  Resonance. 


Resonance  is  defined  by  Brande  as  the  returning  of  sound  by  the  air  acting 
on  the  bodies  of  stringed  musical  instruments.  M.  Savart’s  apparatus  (Fig. 
444)  is,  perhaps,  the  most  perfect  contrivance  for  showing  how  sound  may  be 
strengthened.  We  know,  in  ordinary  musical  instruments,  such  as  the  violin 
and  violoncello,  that  the  mere  vibration  of  the  strings,  unless  strengthened  by 


RESONANCE. 


547 


the  hollow  body  would  give  but  a  feeble  sound.  So  with  Savart’s  arrangement, 
a  hemispherical  bell  is  sounded  by  drawing  a  violin  bow  across  the  edge. 

The  quantity  of  sound  produced  is  very  moderate,  and  the  bell  does  not 
give  a  loud  sound ;  but  directly  the  mouth  of  the  cylindrical  box,  made  ot 
papier  indche,  the  precise  length  and  breadth  of  which  has  been  carefully 
adjusted,  is  brought  round  and  facing  the  vibrating  metal,  the  sound  is  instantly 
and  enormously  increased,  because  the  air  set  in  motion  by  the  bell  communi¬ 
cates  its  viorations  to  the  cylindrical  box,  a  greater  surface  is  thrown  into  the 
same  trembling  condition  as  the  bell,  and,  as  the  two  sympathise  and  are  in 
unison  with  each  other,  the  combined  tremblings  of  the  bell  and  reverbera¬ 
tions  of  the  box  mutually  assist  and  exalt  each  other.  Whilst  a  loud  sound 
is  being  obta-ned,  it  is  very  curious  and  striking  to  notice  the  difference  of 
effect  when  the  mouth  of  the  cylinder  is  turned  away  from  the  bell. 

It  is  not  every  cylinder  of  any  depth 
or  breadth  that  will  answer  the  pur¬ 
pose.  This  is  shown  by  another  expe¬ 
riment  with  a  tuning-fork  and  bottle: 
the  former,  when  struck  and  vibrating, 
must  be  applied  to  the  ear  to  be  heard; 
but,  if  held  over  the  little  bottle,  the 
.  .  sound  is  loud  enough  to  be  heard  in  a 

Fig.  445.  funing-fork  vibrating  ]arge  room,  and  yet  it  entirely  fails 
held  over  the  mouth  of  a  Bottle.  when  another  and  larger  bottle  is  used. 
When  a  tuning-fork  is  mounted  on  a  box,  the  sound  is  strengthened  and  is 
much  louder,  in  consequence  of  the  resonance  of  the  hollow  box. 


Fig.  446. 

A,  Tuning-fork  fixed  on  a  box,  sounded  bv  drawing  a  violin-bow  across  it ;  b,  ditto,  sounded  in  the 

ordinary  manner. 


Professor  Morton,  of  the  Stevens  Institute,  Hoboken,  New  York,  has 
arranged  a  beautiful  experiment  for  showing  how  sympathetic  vibrations  can 
be  set  up  in  another  similar  quiescent  tuning-fork  by  vibrating  one  at  a  dis¬ 
tance  of  20  feet  or  more  from  the  other.  The  tuning-fork  to  be  acted  on  has 
a  minute  pith-ball  attached  to  one  of  the  arms,  and  of  course,  when  placed  in 
the  magic  lantern,  a  picture  of  the  fork,  12  or  more  feet  high,  is  projected  on 
the  screen,  and  the  little  ball  is  proportionately  magnified.  On  vibrating 

35 — 2 


548 


ACOUSTICS. 


another  fork  of  the  same  kind,  the  delicate  movements  by  sympathetic  vibra¬ 
tion,  that  would  otherwise  be  invisible  to  an  audience,  are  made  apparent. 

Mr.  Robert  Spice,  who  assisted  the  writer  in  his  lectures  in  America,  con¬ 
structs  the  whole  apparatus  in  the  most  perfect  manner,  and  has  written  the 
following  paper  on  the  “  Resonance  of  Tuning-Forks,”  which  should  be  read 
by  the  student  before  examining  Tisley’s  Compound  Pendulum  or  Harmono- 
graph  : 

Experiments  on  the  Sympathetic  Resonance  of  Tuning-Forks. 

It  is  well  known  that  a  pair  of  forks  having  a  vibration-number  of  256 
(Koenig’s  Ut3  forks)  show  the  phenomenon  of  sympathetic  resonance  at  dis¬ 
tances  apart  varying  from  3  to  6  feet.  Beyond  6  feet,  special  and  delicate 
means  have  to  be  employed  to  exhibit  their  resonance. 

It  is  also  well  known  that  a  pair  of  forks  having  a  vibration-number  of  512 
(Ut4  forks)  exhibit  the  phenomenon  with  similar  intensity  at  far  greater  dis¬ 
tances.  The  accepted  solution  of  this  difference  of  deportment  is,  that  as  in 
the  latter  case  double  the  number  of  impulses  are  delivered  in  a  second,  con¬ 
sequently  double  the  energy  is  conveyed  to  the  distant  fork. 

If  this  explanation  be  sufficient,  the  following  result  should  follow  :  Forces 
radiating  from  a  centre  obey  the  law  of  inverse  squares  ;  hence,  if  the  amount 
of  motion  (or  force  ?)  received  by  an  Ut3  fork  at  a  distance  of  6  feet  from  its 
excited  fellow  be  represented  by  «,  then  (assuming  an  Ut4  fork  to  have 
double  the  energy  of  an  Ut3  fork)  clearly  the  amount  of  motion  received  by 
an  Ut4  fork  at  a  distance  of  12  feet  from  its  excited  fellow  should  be  repre- 

n 

sented  by  7.  But  so  far  is  this  from  being  the  case,  that  the  intensity,  instead 

of  being  one-half  (as  calculated),  is  more  than  double.  In  fact,  at  20  feet  the 
intensity  of  resonance  of  Ut4  forks  is  undoubtedly  gf eater  than  the  intensity 
of  U t3  forks  at  6  feet. 

A  pair  of  forks  were  cast  in  a  kind  of  bell  metal,  and  tuned  to  Ut3.  On 
Koenig’s  boxes  the  resonance  was  quite  obvious  at  20  feet,  and  at  40  feet  the 
responding  fork  drove  a  cork  ball  of  8mm.  diameter  a  distance  of  10mm. !  This 
result  was  greater  than  that  obtained  with  the  Ut4  forks  of  Koenig.  In  view 
of  these  facts,  it  seemed  to  me  that  a  different  explanation  was  required  to 
clear  up  the  difficulty  ;  and,  after  a  careful  experimental  examination  of  the 
question,  I  offer  the  following  hypothesis  : 

The  intensity  of  sympathetic  resonance  cf forks  on  their  cases  increases  with 
the  angular  deviation  or  motion  of  the  prongs. 

The  question  of  number  of  vibrations  per  second  has  its  proper  value  ;  but 
this  value  is  small  compared  with  the  element  above  stated. 

I  proceed  to  explain  this  hypothesis.  Suppose  that  we  wish  to  set  a  pendu¬ 
lum  in  motion,  but  are  required  to  fulfil  the  two  following  conditions  :  first, 
we  are  obliged  to  hold  the  cord  of  the  pendulum  (point  of  suspension)  in  our 
hand,  and  this  hand  is  also  to  be  the  motive  power,  to  start  and  keep  the 
pendulum  in  motion  ;  second,  we  are  only  to  be  allowed  a  lateral  movement 
of  the  hand  of  1  inch  each  way,  making  in  all  2  inches. 

Now,  the  amount  of  motion  or  amplitude  of  a  pendulum  is  estimated  by  the 
angle  the  cord  or  rod  makes  with  the  vertical ;  and  clearly,  if  the  point  of 
suspension  moves  laterally,  it  thereby  creates  an  angle.  If,  further,  the  point 
of  suspension  has  a  reciprocal  motion  in  accord  with  the  possible  time  of  the 
pendulum,  then,  by  the  principle  of  the  summation  of  impulses,  the  motion  of 


RESONANCE. 


549 


the  entire  pendulum  will  be  gradually  augmented  up  to  a  limit  determined  by 
well-known  mechanical  theorems.  But  if  amplitude  is  expressed  by  angular 
magnitude,  then,  if  the  initial  angle  be  increased,  the  total  motion  must  be 
acquired  in  less  time  and  be  greater.  From  which  it  follows  that,  retaining 
the  conditions  above  stated,  if  we  operated  on  a  pendulum  io  inches  long, 
we  should  set  it  in  its  maximum  motion  in  less  time  and  with  less  expendi¬ 
ture  of  force  than  if  we  operated  on  a  pendulum  50  inches  long.  Experience 
confirms  this. 

A  fork  vibrates  after  the  manner  of  a  pendulum,  and  may  be  looked  upon 
as  an  inverted  pendulum  ;  but  whereas  the  length  of  a  pendulum  determines 
its  vibrating  period,  the  length  and  thickness  together  determine  the  period  of 
a  fork.  Again,  the  period  of  a  fork  varies  directly  as  the  thickness,  but  in¬ 
versely  as  the  square  of  the  length;  hence  a  small  alteration  of  length  will 
make  a  large  difference  in  its  period  ;  or,  conversely,  a  large  alteration  of 
period  does  not  imply  a  large  difference  in  length. 

From  measurements  made  with  an  electro-chemical  registering  apparatus, 
which  1  designed  for  this  and  similar  investigations,  I  find  that  when  a  fork 
of  the  usual  dimensions  (between  Ut3  and  Ut4)  is  in  vibration,  its  stem  or 
handle  alternately  rises  and  falls  in  accord  with  the  period  of  the  fork,  through 
a  distance  of  about  ^  inch.  When  a  fork  on  its  case  is  influenced  by  a  dis¬ 
tant  fork,  the  case  gives  the  stem  this  up-and-down  motion,  which  is  conveyed 
to  the  prongs,  and  sets  them  in  vibration,  after  the  manner  of  the  hand  start¬ 
ing  a  pendulum,  as  specified  above. 

This  motion  of  inch  may  be  looked  upon  as  a  constant,  and  corresponds 
to  the  2  inch  motion  of  the  hand  in  the  illustration.  If  we  decrease  the 
length  of  the  fork  without  altering  the  constant,  we  thereby  allow  of  a  greater 
initial  angle,  the  result  of  which  we  have  already  noted :  it  is  the  same  as 
shortening  the  pendulum-cord.  This  much  understood,  we  are  in  a  position 
to  explain  the  deportment  of  the  bell  metal  forks  cited.  The  velocity  of 
sound  in  bell  metal  is  much  less  than  in  steel  ;  hence,  retaining  similar  thick¬ 
nesses  in  both  cases,  an  Ut3  fork  in  bell  metal  would  be  shorter  than  an  Ut3 
fork  in  steel,  the  ratio  of  the  length  of  the  steel  to  that  of  the  bell  metal  rang¬ 
ing  as  90:75  Therefore,  though  we  retain  the  vibration-number,  we  gain 
advantage  lrom  the  shortness  of  the  fork,  and  hence  from  the  increase  of 
angular  motion  of  the  prongs. 

It  was  suggested  to  me  that  possibly  bell  metal  had  the  property  of  accept¬ 
ing  motion  more  icadily  than  steel.  To  test  this  point  I  made  a  pair  of  Ut3 
steel  forks,  shorter  than  Koenig’s,  and  of  course  thinner,  in  order  to  retain 
the  vibration-number.  These  forks  behaved  just  like  the  bell  metal  forks. 
Further,  I  made  a  pair  of  Ut4  forks  as  long  as  Koenig's  Ut3  forks,  and  of  course 
thicker.  These  behaved  like  Koenig’s  Ut3  forks.  Finally,  taking  a  Koenig 
Ut3  fork  on  its  case,  and  one  of  the  short  Ut-5  forks  also  on  its  case,  on 
placing  them  20  feet  apart,  it  was  found  that,  on  exciting  Koenig’s  fork,  my 
short  fork  responded  well,  whereas  on  exciting  the  short  fork,  Koenig’s  did 
not  respond  at  all.— Silliman’s  “American  Journal,”  December,  1876. 

A  tuning-fork  is  used  for  musical  purposes  because  it  always  gives  the  same 
note  of  the  same  pitch.  It  has  been  a  great  source  of  annoyance  to  singers 
that  the  concert  pitch  has  been  getting  higher,  and  that  it  has  damaged  and 
will  continue  to  harm  the  delicate  vocal  organs  of  good  singers, who,  emulating 
each  other’s  example,  try  to  outvie  one  another.  The  concert  pitch  is  different 
in  London,  Paris,  Vienna,  and  Milan.  Meetings  of  musical  and  scientific 
men  have  been  held  in  this  country  to  try  to  alter  this  state  of  things,  and  now 


ACOUSTICS. 


55° 


reform  appears  to  be  certain,  because  our  greatest  tenor  has  refused  to  sing  in 
any  other  pitch  than  that  of  the  normal  tuning-fork  of  Paris,  which  gives  870 
vibrations  per  second,  /.<?.,  /rt3,  or  the  sound  produced  by  the  third  open  string 
of  the  violin. 

Mr.  H'entry  Walter  Bates,  in  his  deeply  interesting  work  entitled,  “The 
Naturalist  on  the  River  Amazon,”  gives  a  remarkable  illustration  of  resonance 
in  connection  with  an  insect  of  the  cricket  tribe,  “  which  is  found  in  this  neigh¬ 
bourhood,  the  males  of  which  produce  a  very  loud  and  not  unmusical  sound 
by  rubbing  together  the  overlapping  edges  of  their  wing-cases.  The  notes,”  he 
says,  “are  certainly  the  loudest  and  most  extraordinary  that  I  ever  heard  pro¬ 
duced  by  an  orthopterous  insect.  The  natives  call  it  the  ‘tanand,’  in  allusion  to 
its  music,  which  is  a  sharp  resonant  sound  resembling  the  syllables  ta-na-na,  fa- 
na-na ,  succeeding  each  other  with  little  intermission.  It  seems  to  be  rare  in  the 
neighbourhood.  When  the  natives  capture  one,  they  keep  it  in  a  wickerwork 
cage,  for  the  purpose  of  hearing  it  sing.  A  friend  of  mine  kept  one  for  six 
days.  It  was  lively  only  for  one  or  two  days,  and  then  its  loud  note  could  be 
heard  from  one  end  of  the  village  to  the  other.  When  it  died,  he  gave  me  the 
specimen,  the  only  one  I  was  able  to  procure. 

“  It  is  a  member  of  the  family  Locustidcc ,  a  group  intermediate  between  the 
crickets  (Achetidce)  and  the  grasshoppers  (Acridiidce).  The  total  length  of 
the  body  is  two  inches  and  a  quarter  when  the  wings  are  closed,  has  an 
inflated,  vesicular,  bladder-like  shape,  owing  to  the  great  convexity  of  the  thin 
but  firm  parchmenty  wing-cases,  and  the  colour  is  wholly  pale  green.  The 
instrument  by  which  the  tanana  produces  its  music  is  curiously  contrived  out 
of  the  ordinary  nervures  of  the  wing-cases.  In  each  wing-case  the  inner  edge, 
near  its  origin,  has  a  horny  expansion  or  lobe  upon  one  wing;  this  lobe  has 
sharp  raised  margins  on  the  other,  and  the  strong  r.ervure  which  traverses  the 
lobe  on  the  under  side  is  crossed  by  a  number  of  fine  sharp  furrows  like 
those  of  a  file.  When  the  insect  moves  rapidly  its  wings,  the  file  of  the  one 
lobe  is  scraped  sharply  across  the  horny  margin  of  the  other,  thus  producing 
the  sounds,  the  parchmenty  wing-cases  and  the  hollow  drum-like  space 
which  they  inclose  assisting  to  give  resonance  to  the  tones.  The  projecting 
portions  of  both  wing-cases  are  traversed  by  a  similar  strong  nervure ;  but  : 
this  is  scored  like  a  file  only  in  one  of  them,  in  the  other  remaining  perfectly  j 
smooth.  Other  species  of  the  family  to  which  the  tanana  belongs  have  similar  ' 
stridulated  organs,  but  in  none  are  these  so  highly  developed  as  in  this  insect.  | 
They  exist  always  in  the  males  only,  the  other  sex  having  the  edges  of  the  f 
wing-cases  quite  straight  and  simple.  The  mode  of  producing  the  sounds  and 
their  object  have  been  investigated  by  several  authors  with  regard  to  certain 
European  species.  They  are  the  call-notes  of  the  males. 

“  In  the  common  field-cricket  of  Europe  the  male  has  been  observed  to  place 
itself,  in  the  evening,  at  the  entrance  of  its  burrow,  and  stridulate  until  a  fe-  | 
male  approaches,  when  the  louder  notes  are  succeeded  by  a  more  subdued  tone,  i 
whilst  the  successful  musician  caresses  with  his  antennae  the  mate  he  has  won. 
Any  one  who  will  take  the  trouble  may  observe  a  similar  proceeding  in  the 
common  house-cricket.  The  nature  and  object  of  this  insect  music  are  more  j 
uniform  than  the  structure  and  situation  of  the  instrument  by  which  it  is 
produced :  this  differs  in  each  of  the  allied  families  above  mentioned.  In  the 
crickets  the  wing-cases  are  more  symmetrical ;  both  have  straight  edges  and 
sharply  scored  nervures,  adapted  to  produce  the  stridulation.  A  distinct  por¬ 
tion  of  the  edges  is  not,  therefore,  set  apart  for  the  elaboration  of  a  sound- 


VIBRATIONS  OF  STRINGS. 


55i 


producing  instrument.  In  this  family,  the  wing-cases  lie  flat  on  the  back  of 
the  insect,  and  overlap  each  other  for  a  considerable  portion  of  their  extent. 
In  the  Locustida  the  same  members  have  a  sloping  position  on  each  side  of 
the  body,  and  do  not  overlap,  except  to  a  small  extent  near  their  bases.  It  is 
out  of  this  small  portion  that  the  stridulating  organ  is  contrived.  Greater  reso¬ 
nance  is  given  in  most  species  by  a  thin  transparent  piate,  covered  oy  a  mem¬ 
brane,  in  the  centre  of  the  overlapping  lobes. 

“  In  the  grasshoppers  ( Acridiidce )  the  wing-cases  meet  in  a  straight  suture, 
and  the  friction  of  parts  of  their  edges  is  no  longer  possible.  But  Nature 
furnishes  the  same  fertility  of  resource  here  as  elsewhere,  and,  in  contriving 
other  methods  of  supplying  the  males  with  an  instrument  for  the  production 
of  call-notes,  indicates  the  great  importance  which  she  attaches  to  this  func¬ 
tion.  The  music  in  the  males  of  the  Acridiidce  is  produced  by  the  scraping 
of  the  long  hind-thighs  against  the  horny  nervures  of  the  outer  edges  of  the 
wing-cases,  a  drum-shaped  organ,  placed  in  a  cavity  near  the  insertion  of  the 
thighs,  being  adapted  to  give  resonance  to  the  tones.” 


VIBRATIONS  OF  STRINGS,  RODS,  PLATES,  AND 
COLUMNS  OF  AIR. 

The  tuned  string,  according  to  one  of  our  best  dictionaries,  means  “the  chord 
of  a  musical  instrument,  as  of  a  harpsichord,  harp,  or  violin.”  The  definition  is  to 
a  certain  extent  philosophical,  as  the  amount  of  vibration  or  undulation  com¬ 
municated  by  a  string  alone  to  the  air  would  be  too  small  to  be  audible.  It  is, 
therefore,  necessary  to  connect  the  string  with  a  sounding-board ;  and  thus 
the  sound  of  violins  or  pianos  is  found  to  depend  mainly  on  that  part  of  the 
instrument ;  hence  the  great  care  bestowed  on  the  construction  of  the  sound¬ 
ing-board. 

There  are  two  sets  of  vibrations  which  can  be  set  up  in  strings: 

I.  Longitudinal,  or  those  which  are  produced  in  the  direction  of  the  length. 

II.  Transversal,  or  those  which  are  perpendicular  to  the  string. 

In  the  explanation  of  the  monochord  (p.  485),  we  have  already  spoken  of 
those  vibrations  which  belong  to  the  latter  class,  and  are  of  so  much  import¬ 
ance  in  music.  Four  laws  rule  these  vibrations : 

I.  The  stretching  power  being  always  the  same,  or  tension  constant,  the 
number  of  vibrations  per  second,  or  any  other  period  of  time,  is  inversely 
proportional  to  the  length. 

II.  The  number  of  vibrations  are  in  the  inverse  ratio  of  the  squares  of  the 
diameter  of  the  string. 

III.  The  rate  of  vibration  is  directly  as  the  square  root  of  the  stretching 
weight. 

IV'.  The  number  of  vibrations  of  the  string  is  inversely  proportional  to  the 
square  root  of  its  density. 

In  a  series  of  experiments,  where  strings  made  of  various  substances,  such 
as  catgut,  steel  or  copper  wire,  string,  &c.,  are  used,  the  number  of  vibrations 
is  inversely  proportional  to  the  square  root  of  the  weight  of  the  string. 

The  division,  of  the  string  into  ventral  segments — the  parts  where  the 
greatest  movement  occurs  -and  nodal  points,  or  points  of  rest,  has  already 
been  mentioned  in  connection  with  the  monochord,  and  has  been  further 


552 


ACOUSTICS. 


elucidated  in  the  article  on  the  Undulatory  Theory  of  Light  (pp.  6  and  7, 

Figs.  4  and  5).  . 

“It  follows,”  says  Marloye,  “that  as  the  transverse  vibrations  of  strings 
are  in  the  inverse  ratio  of  their  diameters  and  in  the  inverse  ratio  of  their 
lengths,  knowing  the  number  of  vibrations  made  by  a  given  string,  this  string 
can  serve  to  determine  the  number  of  vibrations  of  any  sound  whatever,  if  it 
be  stretched  on  a  suitable  instrument,  since  we  can  thence  easily  deduce  the 
number  of  vibrations  which  any  portion  of  this  string  ought  to  perform. 


Fig.  447. — Differential  Sonometer,  usually  provided  with  an  assortment  of 

Weights. 


“This  apparatus  is  provided  with  three  divided  rules.  The  first  gives  the 
modified  chromatic  gamut ;  the  second  gives  the  true  chromatic  gamut,  and 
also  the  harmonic  divisions  of  the  string;  and  the  third  is  a  French  mitre 
(about  3  ft.  3  in.),  divided  into  y^Vo  Parts  its  length  from  end  to  end.  With 
this  apparatus  and  Marloye’s  tuning-fork,  we  can  take  the  number  of  vibra¬ 
tions  of  any  sound  whatever  in  less  than  a  minute,  by  referring  to  the  table 
which  accompanies  the  apparatus.) 

“  To  verify  the  law  of  tensions  with  this  instrument,  we  stretch  a  string  with 
the  sum  of  the  weights ;  then,  by  means  of  tuning-pegs  attached  to  the  instru¬ 
ment,  we  stretch  a  second  string  which  we  bring  into  unison  with  the  first ; 
we  then  reduce  by  three-fourths  the  weight  attached  to  the  first  string,  and  we 
compare  its  sound  with  that  of  the  string  which  is  fixed. 

“  For  the  verification  of  the  law  of  diameters,  we  compare  alternately  the 
sound  of  strings  whose  diameter  is  known  with  that  of  the  fixed  string,  which 
we  bring  into  unison  with  one  of  them.  We  proceed  again  in  the  same  way 
for  the  law  of  densities ;  but  for  that  of  lengths,  as  for  other  experiments,  we 
only  make  use  of  the  fixed  string,  to  which  we  then  give  the  degree  of  tension 
adapted  to  make  it  sound  as  well  as  possible. 

Longitudinal  Vibrations  of  Strings. 

“  In  strings  of  the  same  substance,  which  vibrate  longitudinally,  the  numbers 
of  vibrations  are  in  the  inverse  ratios  of  their  lengths,  whatever  may  be  their 
diameter  and  tension.  Nevertheless,  in  taking  the  half  of  the  string  with  the 
bridge,  we  have  always  less  than  the  octave  of  the  entire  string ;  and  that  evi¬ 
dently  is  owing  to  the  string  vibrating  between  two  immovable  points,  although 
shorter  by  half,  since  the  harmonic  sounds  the  octave. 

“  Marloye’s  apparatus  for  demonstrating  the  laws  of  longitudinal  vibrations 
tor  strings  of  metai,  and  other  experiments,  is  made  of  mahogany,  and  is  a 


VIBRATIONS  OF  RODS. 


553 


companion  to  the  differential  sonometer.  Its  extremities  are  furnished  with 
handsome  bronze  vices,  acting  as  fixed  bridges,  and  made  to  oppose  the  trans¬ 
mission  of  vibrations  beyond  the  extremities  of  the  string;  thus  the  strings 
stretched  on  this  apparatus  vibrate  with  such  facility  that  we  obtain  from  them 
a  very  pure  sound  by  rubbing  them  gently  near  their  extremity  with  the  end  of 
a  bow.  As  in  the  differential  sonometer,  a  mitre,  divided  into  Part-S, 

separates  the  two  bridges,  and  the  strings  are  stretched  as  we  please,  either 
by  weights  or  by  pegs.  A  movable  pair  of  leaden  pincers  and  a  divided  rule 
permit  us  to  make  the  gamut  either  longitudinal  or  transversal. 

Longitudinal  Vibrations  of  Rods. 


“  In  rods  of  the  same  material  the  numbers  of  vibrations  are  in  the  inverse 
ratio  of  the  lengths,  whatever  be  their  form  and  diameter. 

‘‘For  this  demonstration  four  steel  rods  are  used,  viz.,  two  cylinders  of  a 
metre  in  length  and  of  different  diameters,  one  flat,  of  the  same  length,  and 
one  cylindrical,  shorter  by  one-half ;  also  four  deal  rods. 


Fig.  44.8. 

Mar  bye's  Musical  Instrument 
founded  on  Longitudinal  Vibrations. 


“Although  the  law  just  expressed  is 
considered  as  a  general  law,  it  appears 
notwithstanding  to  have  its  limits,  like 
many  other  laws  of  acoustics.  I  thought 
it  would  appear  curious,”  says  Mar- 
loye,  “to  show  at  acoustic  lectures 
that  a  hollow  tube  sounds  as  if  it  were 
full;  for  that  purpose  1  had  brass  tubes 
and  rods  of  the  same  ciameter  drawn, 
and  I  then  saw,  contrary  to  my  expect¬ 
ation,  that  the  rapidity  of  sound  is 
always  greater  in  a  tube  than  in  a  rod 
when  the  alloy  is  sensibly  the  same; 
thus,  for  example,  for  a  metre  in  length 
the  tube  sounds  about  half  a  note  higher 
than  the  rod.  Still,  >f  the  thickness  of 
the  sides  of  the  tube  be  the  third  of  its 
interior  diameter,  it  sounds  pretty  near¬ 
ly  as  if  it  were  full. 

“The  foot  of  this  instrument  is  com¬ 
posed  of  a  stand,  on  which  is  raised  a 
plank  of  deal,  2  ft.  "j\  in.  high,  i  ft.  in. 
oroad,  and  2j  in.  thick.  On  this  foot 
are  implanted  twenty  deal  rods,  the 
longest  of  which  is  about  5  ft.  3  in. 
Commencing  from  this,  the  succession 
of  white  rods  forms  the  diatonic  gamut, 
and  the  half-notes,  which  complete  this 
gamut  and  render  it  chromatic,  are  re¬ 
presented  by  red  rods. 

“  This  instrument,  which  is  played  on 
by  rubbing  the  sticks  with  the  fingers, 
which  we  previously  dip  into  powdered 
rosin,  yields  very  sweet  tones,  that  can 


554 


ACOUSTICS. 


I 


be  swelled  or  diminished  at  pleasure,  and  give  this  instrument  much  expression 
in  the  hands  of  any  person  who  can  play  well  on  it.” 

Vibrating  Plates. 

In  plates  of  a  similar  kind,  the  numbers  of  vibrations  are  in  the  inverse 
ratio  of  their  homologous  dimensions ;  and  in  plates  of  the  same  shape,  the 
numbers  of  vibrations  are  in  the  direct  ratio  of  their  thickness,  and  in  the 
inverse  ratio  of  their  surfaces. 

The  apparatus  for  demonstrating  the  laws  of  vibrations  of  vibrating  plates 
(Fig.  433,  p.  474)  is  composed  of  a  table  surmounted  by  six  plates  of  brass, 
three  round  and  three  square.  In  the  three  plates  of  the  same  form,  two  are 
alike,  two  whose  thicknesses  are  as  1  :  2,  and  two  whose  surfaces  are  as  1  :  4 

It  has  already  been  explained  (p.  503,  Fig.  444),  in  the  experiment  with 
Savart’s  bell  apparatus  with  resounding  tube,  that  if  we  cause  a  bell,  a  plate, 
or  any  other  substance  which  has  a  certain  extent  of  surface  to  sound,  and 
present  to  a  ventral  segment  of  its  vibrations  the  orifice  of  a  tube  open  at 
both  ends  or  closed  at  one  end,  this  tube  sounds  with  energy  if,  by  its  dimen¬ 
sions,  it  be  in  unison  with  the  vibrating  substance. 

These  circular  plates  are  all  fitted  for  experiments  on  the  rotation  of  lyco¬ 
podium. 

When  the  elasticity  varies  in  a  circular  plate  so  as  to  give  different  axes,  if 
we  act  on  this  plate  with  a  bow  at  the  extremity  of  two  of  these  axes,  or  be¬ 
tween  two  axes,  the  fundamental  note  that  it  will  yield  will  differ  for  each  case, 
as  also  the  figure  which  the  sand  will  assume, 

Marloye  constructed  an  apparatus  for  demonstrating  that  the  rotation  of 
lycopodium  on  circular  plates  is  only  owing  to  the  translation  of  the  nodal 
lines  round  the  circle. 

To  make  the  experiment  in  question,  we  bring  the  two  tubes  to  the  length 
corresponding  to  the  note  we  wish  to  make  sound ;  we  strew  the  plate  with 
lycopodium,  we  make  it  vibrate,  and  when  the  sound  is  well  sustained,  and 
the  lycopodium  turns  rapidly,  we  bring  the  tube  over  the  plate.  Then  each 
belly,  or  ventral  segment,  of  vibration  which  passes  under  the  tube  makes  it 
sound,  which  causes  intermissions  in  the  note,  which  at  first  are  very  rapid, 
but  subsequently  become  slow  if  we  cease  to  act  on  the  plate  with  the  bow ; 
nevertheless,  it  often  happens  that,  long  after  the  lycopodium  is  at  rest,  we 
still  hear  waves  passing.  With  respect  to  the 

Transverse  Vibrations  of  Blades  and  Rods, 

in  simple  transverse  vibrations,  the  numbers  of  vibrations  are  in  the  inverse 
ratio  of  the  square  of  their  lengths,  and  in  the  direct  ratio  of  their  thicknesses, 
no  matter  what  be  their  breadth. 

As  an  illustration  of  such  vibrations,  there  is  an  instrument  used  by  savages, 
called  “ claque-bois.”  This  contrivance,  which  the  savages  make  of  hard 
wood,  and  which  they  strike  with  a  stick  of  hard  wood,  Marloye  makes  of 
deal ;  and  it  is  struck  by  a  piece  of  wood  covered  with  leather,  to  make  it  more 
perceptible  that,  independently  of  the  noise  occasioned  by  the  shock,  the  wood 
is  susceptible  of  yielding  very  pure  and  even  very  agreeable  notes.  This 
instrument  is  composed  of  eight  deal  blades,  forming  a  diatonic  octave,  and 
mounted  so  as  to  be  played  on  with  ease. 

A  piano  constructed  of  paving-stones  is  one  of  the  novelties  recently  reported 
from  Pans.  The  Abbe  Moigno  gave  a  lecture  on  sound,  and  exhibited,  amongst 


VIBRATIONS  OF  COLUMNS  OF  AIR. 


555 


other  instruments,  a  piano,  the  keys  of  which  were  large  pebbles  of  various 
shapes  and  sizes,  supported  freely  on  short  tapes,  attached  to  horizontal  and 
parallel  bars  of  wood.  The  pebbles  had,  with  almost  incredible  labour,  been 
selected  to  form  two  full  octaves  of  the  upper  scale,  and  no  doubt  thousands 
had  to  be  picked  up  and  tested  before  the  right  ones  were  found.  Several 
airs  were  played  on  this  singular  instrument  with,  it  is  said,  wonderful  accuracy 
and  effect. 


Longitudinal  Vibrations  of  Columns  of  Air. 

M.  Marloye,  of  Paris,  who  has  made  some  of  the  finest  acoustic  apparatus,  a 
great  deal  of  which  the  writer  possesses,  says,  “  Let  us  recall  to  mind,  in  the  first 
place,  that  when  we  gradually  increase  the  rapidity  of  a  current  of  air  which 
causes  a  tube  long  in  proportion  to  its  diameter  to  vibrate,  we  make  it  yield, 
as  in  the  French  horn,  a  series  of  harmonic  sounds,  passing  rapidly  from  one 
to  the  other,  and  the  relations  of  whose  vibrations  are  to  each  other  as  the 
natural  arrangement  of  numbers,  i,  2,  3,  4,  &c.,  when  the  tubes  are  open  at 
both  ends;  or  in  the  order  of  the  odd  numbers,  i,  3,  5,  7,  &c.,  when  they  are 
closed  at  one  end.* 

“To  show  this,  two  long  glass  tubes,  one  open  and  the  other  closed,  fitting 
to  a  copper  stop-tap  to  regulate  the  current  of  air,  are  used. 

“When  a  column  of  air  vibrates  longitudinally,  the  nodes  of  vibration  are 
always  at  the  ventral  points  and  reciprocally,  and  we  may  close  the  tubes  at 
the  nodes  or  open  it  at  the  bellies  without  the  sound  undergoing  any  change.f 

“  When  a  cylindrical  column  of  air  is  put  in  vibration  by  an  intermitting  cur¬ 
rent  of  air,  as  with  a  French  horn  or  clarionet  mouthpiece,  in  the  first  place, 
if  the  tube  be  turned  so  as  to  form  a  helix,  the  tone  is  sensibly  the  same  as  if 
it  were  straight,  only  the  sound  is  less  loud,  and  is  produced  with  less  facility, 
according  as  the  radii  of  the  curves  are  shorter;  secondly,  it  sounds  with 
more  facility,  and  yields  sounds  of  much  greater  intensity,  when  it  is  terminated 
in  an  expanded  form,  like  a  trumpet,  which,  however,  has  but  little  influence 
on  its  tone ;  thirdly,  the  sounds  it  yields  are  grating  according  as  its  diameter 
is  more  narrow,  no  matter  what  be  the  nature  of  the  sides  of  the  tube  and  of 
the  trumpet-shaped  extremity. 

“  These  facts  are  demonstrated  by  three  tubes  of  the  same  length,  viz.,  two 
of  gutta-percha  of  different  diameters,  and  one  of  vulcanized  india-rubber, 
that  we  may  roll  into  a  spiral  form  when  we  please ;  and,  besides,  two  trumpet- 
shaped  ends,  one  of  them  of  copper,  and  the  other  of  gutta-percha. 

“  When  we  roll  the  caoutchouc  tube  into  a  spiral  on  a  table,  we  observe  it 
to  unroll  itself  during  the  time  it  sounds.” 

The  practical  application  of  our  knowledge  of  the  condition  of  vibrating 


*  “It  is  a  remarkable  fact  that  the  key-notes  of  two  tubes  of  the  same  size,  nic  open  and  the  other 
closed  at  one  end,  when  the  tubes  are  long  and  narrow,  yield  sounds  which  differ  from  each  other  by  a  t 
octave,  the  closed  tube  yielding  the  lower  note  This  can  easily  be  exemp'ilied  on  the  German  Hute  by 
taking  off  the  two  lower  joints,  closing  the  holes  of  the  remaining  portion,  and  blowing  into  it  when 
the  end  of  the  tube  is  closed  and  when  it  is  open.  The  closing  of  the  tube  will  be  found  to  lower  the 
sound  by  nearly  an  octave  ” 

t  “Thus,  for  the  octa  e  of  the  fundamental  note  a  belly  is  formed  at  the  centre  of  the  tube;  that  is 
to  say,  the  air  at  that  part  of  the  tube  is  neither  rarefied  nor  condensed.  Hence  we  may  open  the  tube 
there  without  altering  the  note.  We  might  also  take  off  its  upper  half  without  changing  the  sound. 
When  the  tube  yields  a  twelfth,  or  vibrates  so  as  to  form  bellies  at  each  third  of  its  lengtn,  we  mav  open 
the  tube  at  the  ventral  points,  or  take  off  one-third  or  even  two-thirds  of  its  length,  without  altering 
‘he  sound.” — From  Pouillet's  “Elements  tic  Physique ." 


556 


ACOUSTICS. 


F IG.  449. — Set  of  Experimental  Organ-pipes 
fitted  on  Table ,  and  Bellows. 


columns  of  air  is  well  shown  in  the  construction  of  organ- 
pipes,  of  which  the  drawing  (Fig.  449)  from  Helmholtz’s 
work  is  thus  described  by  Tyndall : 

“  There  are  various  ways  of  agitating  the  air  at  the  ends 
of  the  tubes  and  pipes,  so  as  to  throw  the  columns  within 
them  into  vibration.  In  organ-pipes  this  is  done  by  blow¬ 
ing  a  thin  sheet  of  air  against  a  sharp  edge.  This  produces 
a  flutter,  some  particular  pulse  of  which  is  then  converted 
into  a  musical  sound  by  the  resonance  of  the  associated 
column  of  air.  You  will  have  no  difficulty  in  understand¬ 
ing  the  construction  of  this  open  organ-pipe  (Fig.  450),  one 
side  of  which  has  been  removed,  so  that  you  may  see  its 
inner  parts.  Through  the  tube  t  the  air  passes  from  the 
wind-chest  into  the  chamber  c,  which  is  closed  at  the  top, 
save  a  narrow  slit,  d  e,  through  which  the  compressed  air 
of  the  chamber  issues.  This  thin  air-current  breaks  against 
the  sharp  edge,  a  b ,  and  there  produces  a  fluttering  noise, 


Fig.  4S<* 


EMBOUCHURES. 


L57 


the  proper  pulse  of  which  is  converted  by  the  resonance  of  the  pipe  into  a 
musical  sound.  The  open  space  between  the  edge,  a  b ,  and  the  slit  below  it, 
is  called  the  embouchure.” 

The  nodal  points  and  ventral  segments  in  the  air  of  an  organ-pipe  are  well 
shown  with  an  apparatus  constructed  for  the  writer  by  Mr.  Pichler,  of  Great 
Portland  Street. 

An  organ-pipe  giving  a  certain  note  is  fixed  on  the  top  of  the  table  connected 
with  the  bellows.  By  opening  or  shutting  a  valve,  the  organ-pipe  sounds  or 
is  silent  at  pleasure. 

The  pipe  is  perforated  in  five  places,  into  which  tubes  are  inserted;  oppo¬ 
site  these  are  five  gas-jets. 


13 


Fig.  451. — Pichlet's  Apparatus  for  showing  the  Nodal  Points 

in  Organ-tubes. 


When  the  bellows  is  filled  with  air,  and  the  organ-pipe.  B,  B,  sounded,  two 
of  the  gas-jets,  D  and  F,  are  blown  out  with  the  violence  of  the  movements  of 
the  air  that  belong  to  the  ventral  segments,  and  three,  C,  F.,  o,  remain  lighted, 
because  they  represent  the  places  of  rest,  or  nodal  points.  In  the  successful 
performance  of  this  experiment  it  is,  of  course,  necessary  to  have  very  minute 
jets  of  burning  gas. 

Marloye,  always  so  clear  and  comprehensive,  thus  speaks  of 

Embouchures. 

“In  the  embouchure  en  flute  (as  in  the  organ  and  flageolet)  the  vibrations  are 
produced  perpendicularly  to  the  plane  of  the  upper  lip  of  the  aperture,  by  the 
plate  of  air,  which  becomes  an  aerial  reed  when  it  meets  with  the  slope  of  that 
lip.  From  thence  results,  as  my  apparatus  demonstrates,  that  the  note  given 
is  high  in  proportion  as  the  aperture  is  lower  and  the  currrent  of  air  more 
rapid. 

“In  the  mouthpieces  of  wind  instruments,  such  as  the  French  horn,  the 
trumpet,  the  ophicleide,  &c.,  the  artist’s  lips  act  as  double  reeds.  The  vibra¬ 
tions  to  which  they  give  rise  are  longitudinal,  and  the  sound  produced  be¬ 
comes  higher  according  as  the  cavity  of  the  mouthpiece  presses  the  lips  into 
a  more  narrow  space. 

“  The  mouthpiece  of  the  clarionet,  as  everybody  is  aware,  is  formed  with 
a  single  reed,  whereas  the  reed  is  double  in  the  hautboy  and  the  bassoon  ;  but 
in  both  cases  the  reeds  vibrate  perpendicularly  to  the  column  of  air,  and  the 
acuteness  of  the  note  which  results  increases  with  the  rapidity  of  the  current 
of  air  and  the  pressure  of  the  lips.” 


558 


ACOUSTICS. 


An  harmonium  reed  is  a  vibrating  tongue  of  metal,  and  by  enclosing  this 
in  a  tube  with  glass  sides  the  mechanism  of  the  source  of  the  musical  note  is 
distinctly  seen. 

Professor  Willis  has  shown  that  vowel  sounds  may  be  produced  either  by 
partially  closing  a  conical  cavity  excited  by  a  reed  placed  at  its  apex,  or  in 


Fig.  452. — A  Reed. 


a  column  of  air  in  a  tube  excited  by  a  reed  at  its  closed  end,  the  particular 
vowel  sound  depending  on  the  length  of  the  tube. 

Hence  with  all  the  so-called  talking  heads  from  the  time  of  Albertus  Mag¬ 
nus,  who  constructed  the  brazen  head,  which,  it  was  said,  had  the  power  of 
talking,  and  is  delineated  at  the  commencement  of  this  chapter  (p.  473,  Fig. 
432),  to  the  present  period,  when  the  Anthropoglossos  flashed  upon  the  giddy 
world  of  London  a  simulated  imitation  of  the  human  voice,  it  is  simply  im¬ 
possible  to  include  in  the  space  of  the  models  of  the  human  cranium  or  throat 
the  necessary  apparatus  to  pronounce  the  words  such  as  Faber’s  genuine  ma¬ 
chine  spoke,  and  which,  of  course,  being  an  honest  piece  of  scientific  appa¬ 
ratus,  utterly  and  entirely  failed  to  excite  public  attention  or  to  win  the 
golden  opinions  of  the  multitude  at  the  Egyptian  Hall,  where  it  was  exhibited. 
The  writer  wishes  sincerely  he  could  find  the  whereabouts  of  Herr  Faber. 
He  can  only  hope  he  is  not  dead,  but  still  lives,  and  will  give  to  the  world  (to 
him  ungrateful)  those  important  acoustic  and  mechanical  discoveries  which 
enabled  him  to  imitate  so  closely  the  vocal  organs  of  man. 


THE  REFLECTION,  REFRACTION,  POLARIZATION,  INTER¬ 
FERENCE,  AND  HARMONY  AND  DISCORD  OF  SOUNDS. 

A  most  enlightened  and  honest  reviewer  in  the  “  Edinburgh  Review,”  thus 
speaks  of  those  properties  which  any  student  of  waves  of  light,  sound,  or  water 
would  agree  must  prevail  in  all : 

“  I  f  the  vibrations  of  the  air  really  produce  sound  as  those  of  ether  cause  light, 
sounds  ought  to  show  all  the  well-known  peculiarities  of  wave  motion — reflec¬ 
tion,  refraction,  interference,  and  polarization.  The  familiar  phenomena  of 
echoes  prove  that  sound  is  reflected,  but  not  that  the  reflected  waves  obey  the 
same  law  as  the  waves  of  light.  The  simplest  experiment  to  show  this  is,  perhaps, 
the  following: — Arrange  two  parabolic  mirrors  of  burnished  metal  so  that  their 
axes  coincide,  and  their  cavities  look  at  each  other  at  the  two  points.  At  the 
axes  known  as  the  foci  place  a  ticking  watch  and  the  ear.  The  observer  hears 
the  watch  at  a  distance  at  which  it  is  quite  impossible  to  hear  it  without  the 
mirrors.  A  little  nearer  the  watch,  or  a  little  further  from  it  than  this  point, 
there  is  absolute  silence.  A  single  point  has  thus  been  selected  out  of  space 


HARMONY  AND  DISCORD. 


5S9 


for  a  complicated  effect  of  reflection.  Let  us  now  replace  the  watch  by  a 
bright  point  of  light,  and  the  ear  by  a  sheet  of  note-paper.  The  image  of  the 
point  comes  out  brilliant  and  well  defined  at  the  very  spot  where  the  ear  heard 
the  watch.  The  law  of  reflection  for  the  two  cases  is,  therefore,  identical. 

“  In  the  same  practical  manner,  but  with  different  apparatus,  the  refraction 
of  sound  is  proved ;  and  not  only  this,  but  the  index  of  refraction  of  sound, 
obtained  from  various  solid,  fluid,  or  gaseous  substances,  may  also  be  deter¬ 
mined.”  (See  article  on  Light). 

The  same  writer  says,  “  The  analog)'  between  light  and  sound  is  not 
complete  till  we  compare  them  with  respect  to  another  characteristic  of  wave 
motion — polarization.  If  we  have  an  indefinite  stretched  horizontal  string, 
plucked  aside  horizontally  at  one  of  its  points  and  then  let  loose,  the  point 
will  continue  to  move  in  a  horizontal  plane,  and  its  oscillating  movement  will 
be  transmitted  along  the  string  at  a  certain  rate.  As  each  successive  point 
takes  up  the  motion,  it  oscillates  in  the  same  horizontal  plane  through  the 
string,  and  in  no  other.  The  rapidity  of  propagation  will  be  definite.  If  the 
weight  stretching  the  string  be  considerable  for  the  length,  we  may  have  a 
musical  note.  This  is  an  exact  picture  of  a  ray  of  polarized  light.”  (The 
reader  should  refer  back  to  the  Polarization  of  Light.) 

“Joseph  Sauveur  was  born  in  1653.  For  the  first  seven  years  of  his  life  he 
was  dumb,  and  he  never  could  speak  freely.  He  was  also  deaf,  he  had  a  false 
voice,  and  no  appreciation  of  music.  In  order  to  verify  his  experiments,  he 
was  compelled  to  rely  on  the  friendly  help  of  musicians  accustomed  to  esti¬ 
mate  chords  and  intervals.  His  contemporary,  the  blind  Professor  Saun- 
derson,  taught  optics  in  the  University  of  Cambridge  a  few  years  later,  but 
he  has  won  for  himself  no  abiding-place,  except  among  the  curiosities  of 
science.  In  all  the  discussions  of  the  ancients,  and  up  to  his  time,  certain 
relations  of  the  notes  themselves  (octaves,  fifths,  &c.)  had  been  constantly 
investigated.  All  the  notes  struck  at  one  time  could  be  compared  with  each 
other  by  reference  to  these  intervals ;  no  accurate  comparison  was  possible 
between  two  notes  produced  on  different  days.  Sauveur  first  pointed  out  that 
the  character  of  the  note  depends  on  the  number  of  vibrations  in  a  given 
period  made  by  the  sounding  body.  The  difficulty  was  to  count  them  in  the 
grave  notes,  where  they  are  the  least  rapid.  If  we  take  two  organ-pipes  which 
sound  in  perfect  unison,  and  shorten  one  of  them  a  little,  it  is  well  known  to 
organ-builders  that  a  curious  pulsing  sound,  swelling  and  falling  alternately 
at  regular  intervals,  accompanies  the  notes  when  they  are  both  sounded  to¬ 
gether.  These  pulses  are  called  beats,  and  Sauveur  explained  them  substan¬ 
tially  as  we  do,  by  the  periodic  coincidences  and  oppositions  of  the  condensed 
parts  of  the  two  vibratory  air-columns.  When  the  pipes  produce  concurrent 
effects,  the  loud  pulse  is  heard;  when  they  oppose  each  other,  the  sound  dies 
away.  The  times  of  these  coincidences  and  oppositions  can  be  calculated. 
If  the  ratio  of  the  numbers  of  vibrations  (which  depend  on  the  length  of  the 
air-columns)  be,  let  us  say,  as  8  :  9,  there  will  be  a  beat  at  every  interval  of 
eight  vibrations  of  the  one  and  nine  of  the  other.  If  16  be  heard  in  a  second, 
there  must  have  been  128  vibrations  of  the  one  column  and  144  of  the  other 
in  the  same  time.  Sauveur  found  in  this  way  that  the  grave  do  of  an  8-foot 
organ-pipe  makes  122  vibrations  per  second.  It  is  a  curious  illustration  of 
the  importance  of  his  discovery  and  of  the  difficulty  of  comparisons  between 
the  musics  of  different  periods  which  are  founded  on  anything  but  the  number 
of  the  vibrations,  that  the  note  that  now  goes  by  the  same  musical  name  (the 


56° 


ACOUSTICS. 


grave  do  of  the  violoncello  at  150  C.)  corresponds  in  pairs  to  1  vibrations. 
Chladni  proposed  128  as  a  number  readily  subdivisible.  The  suggestion 
has  been  generally  followed  in  physical  discussions.  The  French  standard 
was  fixed  by  ministerial  decree  in  February,  1859,  and  adopted  at  the  opera 
)t  Vienna,  and  officially  in  Russia  three  years  later.  The  English  standard 
is  1334,  and  the  German  132,  vibrations.  There  has  been  a  gradual  rise  at 
the  Italian  Opera  in  Paris  from  the  days  of  Sauveur  until  the  standard  number 
came  to  be  1 34^  just  before  it  was  reduced  by  decree.  Scheibler  showed  that 
one  note  had  stood  successively  for  86 7,  872,  878,  880,  and  889  vibrations  in 
the  course  of  thirty  years  of  the  present  century. 

********* 

“The  experiment  suggested  by  Sir  John  Herschell  gives  us  two  sounds  re¬ 
sulting  in  silence.  Let  us  imagine  a  tube  like  a  narrow  rectangle,  with  two 
holes  in  the  middle  of  the  two  longer  sides  for  the  insertion  of  long  tubes 
perpendicular  to  them.  On  the  one  side  of  these  tubes  the  whole  arrangement 
is  permanent,  on  the  other  the  rectangle  has  a  sliding  part,  as  in  a  trombone, 
so  that  we  may  draw  it  out  or  push  it  in  at  pleasure.  The  tubings,  therefore, 
which  are  at  first  of  equal  lengths  to  right  and  left  of  the  insertions,  may  be¬ 
come  unequal,  and  by  any  desired  amount.  • 

“At  the  open  end  of  the  one  insertion  let  a  tuning-fork  be  struck;  at  the 
other,  which  should  be  far  enough  removed  to  make  it  impossible  to  hear  the 
tuning-fork  without  the  help  of  the  apparatus,  let  the  observer  place  his  ear. 
The  vibrations  travel  down  the  first  insertion,  but  divide  into  two  halves  to 
right  and  left  of  the  opening  into  the  rectangle. 

“  After  pursuing  their  equal  paths,  they  meet  at  the  opening  opposite,  and 
pass  down  the  second  insertion-pipe  to  make  a  distinct  and  loud  impression 
on  the  drum  of  the  ear. 

“  When  the  right-hand  tube  is  a  little  drawn  out,  the  sound  is  enfeebled ; 
when  it  is  drawn  out  a  certain  length,  it  is  not  heard  at  all.  The  difference  is 
half  a  wave’s  length  of  air,  corresponding  to  the  note  sounded. 

“  Drawn  out  a  little  farther,  the  sound  grows  again,  till,  when  it  has  got 
twice  as  far  as  at  first,  it  is  heard  just  as  distinctly  as  before  the  tube  was 
pulled  out  at  all. 

“  If  we  cut  off  one  of  those  interfering  air-columns  from  passing  into  the 
second  insertion-tube,  the  sound  is  heard  half  as  loud  as  in  the  first  case. 

“  The  silence,  the  double  sound,  and  all  the  shades  of  intermediate  vibra¬ 
tions  which  theory  requires  are  exhibited  in  the  experiment.” 

The  harmony  and  discord  of  sounds  is  admirably  shown  by  another  appa¬ 
ratus,  constructed  by  Pichler.  It  is  time  that  the  idea  of  such  an  apparatus 
is  not  new,  because  M.  Lissajous  has  shown  the  same  facts  with  tuning-forks, 
to  which  mirrors  were  attached  to  reflect  the  rays  from  the  electric,  or  oxy- 
1  y  Irogen,  or  oil-lamp  light. 

Fielder's  apparatus  is  unique.  It  consists  of  two  harmonium-reeds  with 
mirrors,  one  perpendicular  and  the  other  horizontal.  Upon  the  first  falls  a 
bright  beam  of  light  from  a  proper  lens,  and  this  being  vibrated  or  sounded, 
gives  a  perpendicular  line  of  light  ;  the  horizontal  reed  and  mirror  give  a 
horizontal  line.  These  notes  are  tuned  as  nearly  as  possible  in  unison,  and 
when  they  are  sounded  together,  the  ray  of  light  reflected  from  the  perpen¬ 
dicular  reed  to  the  hoiizontal  one  resolves  itself  into  a  compound  motion, 
which  gives  the  form  of  rings  of  light,  rotating  in  the  most  exquisite  manner. 

There  cannot  be  a  more  perfect  expression  of  human  harmony  than  the 


Fig.  453.-  -Pichler’s  Harmony  and  Discord  Apparatus. 


presentation  of  “  a  plain  gold  ring.”  These  two  sounds  in  harmony  give  the 
figure  of  a  ring,  which  may  change,  like  earthly  affairs,  to  discord.  When  the 


562 


ACOUSTICS. 


two  notes  are  vibrated  in  another  phase,  a  somewhat  confused  picture  is  ob¬ 
served  on  the  disc,  which  changes  again  to  a  “  true  lover’s  knot  ”  as  the 
vibrations  are  altered,  thus  : 

C  natural,  C  bass,  an  8-foot  note,  in  unison  with  another  of  the  same  kind, 
gives  the  ring  of  light. 

E,  gives  the  figure  of  8 — two  rings. 

G,  J, — “  true  lover’s  knot,”  or  three  rings. 

Thus  the  whole  octave  may  be  traced  out  with  beautiful  figures,  all  differing 
from  each  other. 

Harmony  is  heard  and  seen,  and  so  also  is  discord. 

Tisley’s  Compound  Pendulum. 

Tts  chief  object — at  least  for  the  present — is  to  trace  the  beautiful  curves 
corresponding  to  sonorous  vibrations,  and  known  in  science  as  LGsajous’ 
figures. 

While  a  few  mathematicians  have  devoted  their  attention  to  the  investiga¬ 
tion  of  the  properties  of  these  figures,  certain  others  have  expended  a  con¬ 
siderable  amount  of  time  and  ingenuity  in  endeavouring  to  determine  the 
best  means  of  exhibiting  them  both  optically  and  graphically.  In  Lissajous’ 
fundamental  experiment,  familiar  to  every  tyro,  they  are  seen  in  a  mirror  or 
are  reflected  upon  a  screen.  Here,  however,  they  have  but  a  temporary 
existence,  lasting  only  so  long  as  the  tuning-forks  continue  to  vibrate.  The 
same  remark  is  also  applicable  to  Wheatstone’s  kaleidophone,  and  we  may 
add  that  in  both  cases  we  have  only  the  elementary  forms  instead  of  the  full 
complete  tracings  of  the  figures.  Professor  Blackburn,  in  1844,  invented  a 
modification  of  the  pendulum,  in  which  the  bob  could  swing  freely  in  two 
planes  perpendicular  to  each  other.  When  it  was  drawn  out  of  these  planes, 
its  movements  were  compounded  of  the  other  two  modes  of  vibration,  and  in 
its  aerial  course  it  described  figures  identical  with  Lissajous’.  In  1871,  Mr. 
Hubert  Airy,  with  an  apparatus  similar  in  several  respects  to  that  of  Professor 
Blackburn,  got  a  considerable  number  of  varied  and  beautiful  traces,  an 
account  of  which  he  gave  in  “  Nature,”  August  17  and  September  7,  1871. 
This  interesting  subject  has  now  been  taken  up  by  Mr.  Tisley,  and  the  result 
of  his  labours  is  embodied  in  the  compound  pendulum.  This  instrument  is 
not  limited  to  certain  figures  or  certain  classes  of  figures.  It  will  trace  with 
equal  ease  the  elegant  curves  representing  all  the  musical  intervals,  and  an 
endless  variety  of  other  curious  curves  corresponding  to  the  gradual  changes 
between  unison  and  octave,  octave  and  fifth,  and  generally  between  the 
fundamental  and  its  harmonics.  Besides  these  changeful  phases,  it  may 
describe  others  which  have  no  equivalent  in  music.  In  most  cases  such 
figures  will  be  extremely  complex,  but  always  rigorously  symmetrical. 

By  the  optical  method,  the  consonance  or  dissonance,  as  already  stated,  is 
represented  by  a  mere  outline ;  but  the  compound  pendulum,  after  first  tracing 
this  elementary  form,  fills  up  the  enclosed  space  with  an  exact  reproduction 
of  the  same  curve,  always  in  a  gradually  decreasing  scale,  until  the  vibrations 
die  away.  We  thus  have  a  series  of  curves  within  curves,  which  please  by 
their  elegant  form  and  marvellous  regularity  ;  but  the  eye,  gratified  at  first, 
is  soon  bewildered,  and  at  last  is  lost  in  the  midst  of  the  apparently  endless 
gyratory  web.  Mr.  Tisley’s  apparatus  involves  no  very  delicate  or  complicated 
mechanism,  as  may  be  seen  by  the  accompanying  illustration.  Indeed,  its 
extreme  simplicity  strongly  reminds  one  of  the  puzzle  of  Columbus.  The  figure 


TISLE  Y’S  COMPOUND  PENDULUM. 


5  6  3 


shows  this  apparatus  with  the  appliance  for  magnifying  and  reflecting  the 

36 — 2 


564 


ACOUSTICS. 


figures  :  P  P  are  the  two  pendulums,  3  feet  in  length,  carefully  balanced  on 
knife-edges  at  k  k,  and  continued  above  their  axis  of  suspension  to  a  a.  The 
pans  attached  to  several  parts  of  the  pendulums  are  intended  to  receive  the 
weights.  The  sum  of  the  weights  used  at  any  time  varies  from  5  lb.  to  12  lb. 
Some  of  these  are  arranged  to  move  along  the  rods,  in  order  to  facilitate  the 
placing  of  the  weights  at  different  heights,  w  is  a  weight  sliding  along  the 
constant  pendulum  and  attached  to  a  counterpoise,  S,  by  means  of  a  cord 
passing  over  a  pulley  fixed  on  the  bearings.  The  object  of  this  appendage  is 
slightly  to  change  the  relative  rate  of  vibration  whilst  the  pendulums  are  in 
motion,  and  thus  either  obtain  a  small  fraction  of  a  vibration  in  excess  or  else 
adjust  the  vibrations  to  the  greatest  nicety.  Two  arms  of  thin  wire  project 
from  the  upper  part  of  the  pendulums  and  meet  at  right  angles— when  the 
pendulums  are  quiescent— in  o.  Perfect  freedom  of  motion  in  every  direction 
is  attained  by  connecting  these  with  the  pendulum-rods  by  means  of  ball  and 
socket  joints.  The  three  points,  a,  o,  a,  are  so  correlated  as  to  form  three 
angular  points  of  a  square.  Two  threads,  1 1 ,  are  attached  at  their  lower  ends 
to  the  arms  a  c,  and  at  the  upper  to  the  extremities  of  two  bent  wires,  which 
are  fixed  to  a  thin  metallic  rod,  which  is  made  to  slide  through  a  tube,  m. 
These  threads  are  merely  for  convenience  in  raising  or  lowering  the  tracing- 
point,  as  it  is  desirable  to  do  this  without  affecting  in  any  way  the  vibrations 
of  the  pendulums.  This  device  also  affords  an  easy  means  of  swinging  the 
pendulums  and  regulating  their  vibrations  before  beginning  to  take  the 
tracings.  The  rod  terminates  in  a  metallic  disc  under  the  horizontal  table: 
by  simply  pushing  this  button  up  or  dow-n,  the  pen  is  either  raised  or  depressed. 
At  the  intersection  of  the  two  wire  arms,  a  c,  there  is  a  short  angular  bar 
maintained  in  a  vertical  position  by  means  of  a  curved  support.  This  receives 
the  tracing-points  or  pen,  which  is  thus  always  held  perpendicular  to  the 
plane  of  the  underlying  card.  The  pen  is  made  from  a  thin  glass  tube  by 
drawing  out  one  end  into  a  fine  point,  which  in  general  does  not  exceed 
the  500th  part  of  an  inch  in  diameter.  The  ink,  or  coloured  fluid,  which 
must  be  very  mobile,  is  sucked  up  through  this  microscopic  pen-point.  To 
describe  one  of  the  figures  it  is  necessary  only  to  place  the  requisite  weights 
on  the  pendulums,  to  set  these  in  motion,  and  at  the  appropriate  moment  to 
draw  down  the  pen.  Thus  if  we  want  the  curve  corresponding  to  an  octave, 
one  of  the  pendulums  must  make  two  vibrations,  while  the  other  makes  only 
one.  Having  ascertained  this,  we  start  the  pendulums  together;  then  lowering 
the  pen,  beautiful  curves  will  be  traced.  The  time  required  does  not  exceed 
three  or  four  minutes,  and  the  distance  traversed  by  the  pen  in  some  instances 
is  more  than  100  feet.  We  may  observe  the  successive  development  of  the 
figures  by  following  the  motion  of  the  pen  over  the  card,  or  by  looking  at  the 
magnified  image  in  the  reflecting  mirror.  If  it  be  desired  to  exhibit  them  to 
an  audience,  an  oblong  of  blackened  glass  is  substituted  for  the  cards,  when 
an  image  may  be  thrown  upon  a  screen  in  the  usual  way.  It  is  not  easy  to 
imagine  a  more  striking  experiment  than  that  afforded  in  the  present  instance, 
by  the  noiseless  and  gradually  decreasing  sweep  of  a  pen-point  gliding  over 
its  sinuous  path  in  obedience  to  the  oscillations  of  two  conjoined  pendulous 
bodies,  and  tracing  before  the  eyes  of  admiring  spectators  curves  of  maze-like 
intricacy  and  yet  of  faultless  symmetry.  As  in  music,  the  simplest  harmony 
is  the  most  agreeable  to  the  ear,  so  with  these  figures  the  simpler  the  propor¬ 
tion  between  the  vibrations  of  the  pendulums  the  more  pleasing  are  the 
resulting  curves.  Thus  the  ratios  1  :  2,  or  octave ;  2  :  3,  or  fifth,  i  :  3,  or  octave 


TISLEY' S  COMPOUND  PENDULUM. 


565 


and  fifth,  afford  figures  more  graceful  to  the  eye  than  the  ratio  5  :  6,  or  minor 
third,  or  5  :  8,  or  minor  sixth.  We  should  mention,  however,  that  in  such 
cases  as  the  latter,  when  the  consonance  is  not  strictly  perfect— or,  to  use  the 
mechanical  nomenclature,  when  there  is  a  slight  difference  between  the  simple 
proportions  and  the  actual  rate  of  vibration — we  obtain  crossings  or  secondary 
figures,  technically  called  water- marks,  which  are  possessed  of  peculiar 
elegance.  These  are  easily  produced,  when  once  we  have  ascertained  that 
the  pendulums  are  beating  an  exact  ratio,  by  merely  lowering  the  adjusting 
weight,  w. 

Mr.  Tisley  dispenses  with  the  trouble  attending  the  frequent  change  of 
weights  by  making  one  of  the  pendulums — that  which  carries  the  small  ad¬ 
justing  weight — constant,  while  he  quickens  the  vibrations  of  the  other  by 
sliding  the  movable  weights  along  the  rod.  This  will  evidently  shorten  the 
pendulum  and  make  it  move  more  rapidly,  thus  passing  successively  through 
all  the  points  giving  the  various  proportions  from  1  :  1  to  1  :  3.  Mr.  Tisley 
has  also  found  that  by  inverting  tire  constant  pendulum  — that  is,  placing  the 
weight  above  the  axis  of  suspension  as  at  d — the  vibrations  become  much 
slower,  so  that  1  :  1  is  converted  into  3:4;  2:3  into  1:2;  4:5  into  3:5; 
and  all  the  other  intervals  in  proportion.  That  is,  unison  is  changed  into  a 
fourth  ;  a  fifth  into  an  octave  ;  a  major  third  into  a  major  sixth,  &c. 

This  interesting  and  ingenious  apparatus  may  be  taken  to  pieces  in  a  few 
minutes  and  enclosed  within  the  box  shown  in  the  figure ;  and  we  may  say,  it,, 
conclusion,  that  it  certainly  gives  a  simple  and  satisfactory  solution  to  the 
interesting  problem  of  the  graphical  representation  of  sonorous  vibrations. — 
“  Engineering,”  Feb.  6th,  1874. 

Since  the  construction  of  the  compound  pendulum  apparatus,  which  the 
writer  has  used  in  his  lectures,  projecting  the  figures  on  to  the  disc  by  the 
oxy-hydrogen  light,  a  new  and  recent  wonder  has  been  added  to  these  in¬ 
teresting  results  in  the  Stereoscopic  Slides  of  the  curves,  which,  when  pro¬ 
perly  looked  at,  give  wonderfully  solid  figures— in  fact,  show  the  forms  ot 
matter,  of  air,  with  wnich  we  are  surrounded,  in  their  different  vibratory 
phases.  Some  of  these  stereoscopic  pictures  are  in  different  colours,  and  by 
them  it  is  demonstrated  that  the  mind,  which  receives  the  impression  through 
two  different  channels,  recognizes  only  one  sensation,  and  that  is  a  complete 
blending  of  the  two  images  into  one.  The  method  of  taking  these  stereo¬ 
scopic  figures  is  at  present  a  secret. 

Another  novelty  which  Mr.  Tisley  has  in  preparation  is  the  use  of  slides 
formed  on  this  principle  for  showing  the  action  of  crystals  under  polarized 
light,  as  it  was  noticed  by  the  learned  and  educated  eyes  of  the  savans  who 
first  saw  these  stereoscopic  pictures,  that  the  apparatus  not  only  drew  the 
waves  of  sound,  but  also  those  of  polarized  light ;  and  thus  Mr.  Tisley  appears 
to  have  found  the  link  which  connects  the  two. 

The  Tuning-fork  as  a  Telegraphic  Instrument. 

La  Cour  has  devised  a  very  ingenious  use  of  the  tuning-fork  for  transmitting 
signals  on  the  telegraph  lines,  which  promises  to  become  of  great  importance. 
It  is  based  on  the  well-known  fact  that  if  a  given  fork  be  made  to  interrupt  an 
electric  circuit  by  its  vibrations,  and  the  intermittent  current  thus  produced 
be  passed  through  a  series  of  electro-magnets,  each  in  connection  with  a  fork 
of  different  rate,  only  that  fork  will  be  thrown  into  vibration  which  is  in  unison 
with  the  first  one.  Practically  the  time  required  to  do  this  is  the  small  fraction 


ACOUSTICS. 


566 


of  a  second.  The  advantages  of  this  method  are  numerous.  Not  only  may 
many  receiving  instruments  at  one  station  be  operated,  each  by  its  own  key, 
through  a  single  wire,  but  many  different  stations  in  the  same  circuit  may  be 
operated,  that  one  alone  receiving  the  message  which  has  the  requisite  instru¬ 
ment.  Moreover,  many  signals  may  in  this  way  be  transmitted  over  the  same 
wires  at  the  same  time,  and  as  many  despatches  sent  simultaneously  to  as 
many  stations.  All  this  may  be  done,  too,  without  affecting  the  line  for  its 
ordinary  use,  and  independent  of  atmospheric  and  terrestrial  currents. 


THE  TRANSMISSION  OF  SOUNDS  THROUGH  GASEOUS, 
LIQUID,  AND  SOLID  MEDIA. 

The  progress  of  sound  through  air  and  the  manner  in  which  it  travels  has 
already  been  discussed ;  it  is  only  necessary  to  speak  of  the  velocity  of  sound, 
in  which  the  relation  between  density  and  elasticity  is  well  shown.  As  the 
propagation  of  sonorous  waves  is  gradual,  sound  requires  time  for  its  trans¬ 
mission  from  one  place  to  another.  According  to  the  French  and  Dutch 
philosophers,  the  velocity  of  sound  at  26'6°  C.  is  1,140  feet  per  second.  At 
the  freezing  temperature,  o°  C.,  the  velocity  is  diminished  to  1,090  feet  per 
second :  here  the  density  is  increased,  the  elasticity  of  the  air  remaining  the 
same.  An  increase  in  the  temperature  of  the  air  equal  to  ic  causes  a  corre¬ 
sponding  increase  of  ri4  feet  per  second  in  the  velocity  of  sound:  here  the 
density  being  diminished,  the  elasticity  remains  the  same.  The  velocity  is 
directly  proportional  to  the  square  root  ol  the  elasticity  of  the  air,  and  in¬ 
versely  as  the  square  root  of  the  density. 

Sound,  in  fact,  travels  through  different  media  with  very  different  degrees  of 
velocity ;  thus,  starting  with  air  as  unity  or  one,  the  following  velocities  have 
been  determined : 


Distilled  water 

4‘5 

Laplace. 

Brass  . 

105 

Laplace. 

Sea-water 

47 

Copper 

1 2'0 

Chladni. 

Tin 

T  5 

Chladni. 

Hammered  iron  . 

\yo 

Silver  . 

9-0 

Glass  . 

iyo 

Cast  iron 

IO'O 

Bibet. 

Wood  .  .  n  '0  to 

\go 

It  is  apparent  from  the  above  table  that  the  velocity  does  not  depend  only 
on  the  density  of  the  body  transmitting  the  sound,  but  in  a  greater  degree  on 
its  elasticity. 

Tyndall  shows  from  his  own  observations  that  the  intensity  of  sound  de¬ 
pends  on  the  density  of  the  air  in  which  it  is  generated ,  and  not  on  that  of 
the  air  in  which  it  is  heard.  As  an  illustration,  he  supposes  the  case  of  two 
cannon  with  equal  charges,  the  one  fired  from  a  lofty  mountain,  such  as  the 
summit  of  Mont  Blanc,  and  the  other  from  Chamouni ;  the  latter,  being  fired 
in  heavy  air,  may  be  heard  above,  whilst  the  former,  being  fired  in  rarefied 
air,  is  unheard  below.  He  further  remarks: 

“  There  is  no  mistake  more  common  than  to  suppose  the  velocity  of  sound  to 
be  augmented  Oy  density.  The  mistake  has  arisen  from  a  misconception  of 
the  fact  that  in  solids  and  liquids  the  velocity  is  greater  than  in  gases. 


TRANSMISSION  OF  SOUNDS. 


567 


“  But  it  is  the  high  elasticity  of  those  bodies  in  relation  to  their  density  that 
causes  sound  to  pass  rapidly  through  them. 

“  Other  things  remaining  the  same,  an  augmentation  of  density  always 
produces  a  diminution  of  velocity.” 

The  laws  that  govern  the  propagation  of  sound  are  very  similar  to  those 
which  rule  the  progress  of  light. 

The  intensity  of  sound  is  in  the  inverse  ratio  of  the  square  of  the  distance 
of  the  sonorous  body  from  the  ear. 

If  one  bell  affords  a  certain  ameunt  of  sound  at  a  distance  of  100  ft.,  it  will 
require  four  bells  of  equal  power  to  affect  the  auditory  nerves  to  the  same 
amount  at  200  ft.,  or  double  the  distance. 

It  is  said  that  an  experienced  general,  walking  on  the  heights  of  Dover, 
predicted  that  a  great  battle  was  being  fought,  from  the  sounds  which  his  ex¬ 
perienced  ear  detected ;  and  taking  down  the  hour  and  date,  they  tallied  exactly 
with  the  time  of  the  hottest  part  of  the  firing  on  the  field  of  Waterloo.  The 
higher  the  waves  of  water,  the  louder  the  roar  as  they  dash  on  the  rocky  shore. 
The  intensity  of  sound  is  proportional  to  the  square  of  the  amplitude  or  largeness 
of  the  undulation,  and  also  to  the  square  of  its  maximum  velocity ;  it  is  also 
modified  by  the  motion  of  the  air.  Sounds  are  propagated  better  in  calm 
than  in  stormy  weather,  also  with  more  intensity  in  the  direction  of  the  wind 
than  in  the  contrary  direction. 

A  modification  of  the  law,  that  the  intensity  of  sound  varies  inversely  as 
the  square  of  the  distance,  takes  place  when  sound  is  caused  to  travel  through 
long  smooth  tubes.  The  sound  moves  like  the  rings  produced  in  a  pool  of 
water  by  a  falling  stone:  they  are  no  longer  spread  out  laterally  until  they  fade 
away  to  silence,  but  are  transmitted  without  any  perceptible  alteration  from 
one  end  of  the  tube  to  the  other. 


F 1 G.  455. — The  Speaking-  Trumpet. 


The  common  speaking-trumpet,  which  is  a  conical  metal  tube,  made  wide 
at  one  end  like  a  funnel,  called  the  “  bell,”  and  furnished  with  a  mouthpiece 
at  the  other,  is  of  great  use  to  captains  of  vessels  and  pilots  in  giving  the 
necessary  orders  during  the  noise  that  prevails  in  stormy  weather.  The  re¬ 
flection  of  the  sound-waves  from  the  sides  of  the  tube,  and  the  positive  direc¬ 
tion  given  to  tlum,  may  probably  explain  the  cause  of  the  strengthening  of 
the  voice,  which  is  as  much  increased  as  if  the  trumpet  represented  the  mouth 
of  a  giant  with  his  lips  wide  open. 

The  empty  water-pipes  of  Paris  were  placed  at  the  disposal  of  Biot,  the 
great  French  philosopher,  and  though  he  spoke  in  a  whisper,  his  voice  was 
distinctly  heard  through  a  distance  of  upwards  of  3,000  yards,  a  range  which 
any  experienced  rifleman  would  fully  appreciate. 

A  hollow  tube  placed  on  the  region  of  the  heart  or  lungs,  and  applied  to  the 
experienced  ear  of  a  medical  man,  enables  him  to  form  an  opinion  of  the  state 
of  these  organs,  the  instrument  being  called  the  Stethoscope. 


568 


ACOUSTICS. 


Fig.  456.  —  The  Invisible  Girl. 


The  practical  application  of  lliot’s  experiment  was  soon  made  in  England, 
and  now  there  is  hardly  an  office  (where  the  clerks  have  to  sit  on  different 
floors)  which  is  not  fitted  with  speaking-tubes. 

The  cut  (Fig.  432,  p.  473)  at  the  head  of  the  chapter  on  acoustics,  graphi¬ 
cally  depicts  the  old  story  of  the  speaking  head  of  Albertus  Magnus,  which  is 
said  to  have  been  dashed  to  pieces  by  his  worthy  pupil,  Thomas  Aquinas, 
perhaps  because,  knowing  the  voice,  he  would  not  have  his  understanding 
insulted  with  such  a  shallow  trick.  Here  again  the  hollow  tube  conveys  the 
sound  from  the  mouth  of  the  concealed  master  to  the  ear  of  his  warm-tempered 
pupil. 

The  Anthropoglossos,  or  speaking  head,  and  “human  voice,”  exhibited  in 
London  as  a  genuine  mechanical  talking  head,  which  they  pretended  to  wind 
up,  was,  of  course,  only  a  modification  of  the  above  old  story,  and  not  one- 
quarter  so  clever  as  the  famous  invisible  girl,  which  really  puzzled  the  cockney 
wiseacres  many  years  ago. 

The  cut  (Fig.  456)  explains  itself,  and  clearly  shows  the  hollow  tube  passing 
under  the  floor.  At  one  end  is  a  girl,  who  receives 
and  answers  questions;  at  the  other,  and  sus¬ 
pended  in  a  sort  of  ornamental  bedstead,  are  the 
trumpets  attached  to  a  hollow  globe,  as  delineated 
in  Fig.  457,  and  demonstrating  that  the  main  pipe 
came  up  one  of  the  posts  of  the  bedstead,  and 
then  was  connected  with  two  pipes  placed  oppo¬ 
site  the  mouths  of  the  trumpets. 

At  the  Polytechnic  a  speaking  head  was  shown, 
and  explained  to  be  due  to  the  same  kind  of 
arrangement,  the  writer’s  assistant  being  con¬ 
cealed  in  an  adjoining  apartment,  to  which  a 
gutta-percha  pipe  passed,  terminating  in  a  hollow 
head  with  a  movable  jaw.  Fig.  457. 

When  the  eyes  are  deceived  simultaneously  The  Globe  and  Trumpets. 


TRANSMISSION  OF  SOUNDS. 


569 


with  the  ears,  acoustic  illusions  are  greatly  enhanced ;  thus,  a  striking  bell 
deprived  of  its  clapper,  and  placed  upon  the  table,  apparently  yields  a  sound 
when  the  stud  is  pressed  down,  whereas  it  is  the  foot  pressing  on  the  stud  of 
another  striking  bell  under  the  table  that  really  yields  the  sound. 

Dulong’s  table  of  the  velocity  of  sound  per  second  through  air  and  some  of 
the  gases,  at  a  temperature  of  o°  C.,  may  well  complete  this  part  of  the  subject. 


Air 

Oxygen 
Hydrogen 
Carbonic  acid 


Velocity. 


1,092 

feet 

1,040 

4,164 

00 

VTA 

00 

Carbonic  oxide 
Protoxide  of  Ni¬ 
trogen 
Olefiant  gas 


Velocity. 
1,107  feet 

859  ,, 
1,030  „ 


Transmission  of  Sound  through  Liquids. 

1  he  celebrated  Dr.  Franklin  ascertained  that  liquids  conducted  sound,  by 
placing  an  assistant  half  a  mile  from  himself,  who  was  directed  to  continue  to 
strike  U/o  stones  together  under  the  water.  The  doctor  did  not  take  a  “header,” 
though  he  placed  his  own  head  under  water,  and,  it  is  said,  distinctly  heard 
the  sound  caused  by  the  knocking  together  of  the  stones. 

Colladon  and  Sturm’s  experiments  on  and  in  the  Lake  of  Geneva  have 
always  been  quoted  as  most  excellent  and  trustworthy.  They  determined  that 
the  velocity  of  sound  in  water  was  4,708  feet  per  second ;  subsequently  Wer- 
thcim  determined  that  the  velocity  of  sound  in  the  water  of  the  Seine,  at  a 
temperature  of  150  C.,  was  4,714  feet  per  second,  or  six  feet  per  second  faster 
than  that  recorded  by  Colladon  and  Sturm.  This  difference  was  probably  due 
to  temperature,  the  water  of  the  Lake  of  Geneva  being  colder  at  the  time 
than  that  cf  the  River  Seine. 

Salts  dissolved  in  water  increase  the  velocity'  of  sound,  and  especially 
chloride  of  calcium.  The  velocity  of  sound  in  water  increases,  like  that  in 
the  air,  with  the  temperature,  and  sound  was  found  to  travel  at  the  rate  of 
5,657  feet  per  second,  at  a  temperature  of  6o°  C,  through  the  water  of  the 

Seine. 


Transmission  of  Sound  through  Solid  Conductors. 
Wertheim’s  table  is  a  good  preface  to  Wheatstone’s  admirable  experiments. 


Name  of  Metal. 

At  200  c. 

At  ioo°  C 

At  2000  C 

Lead 

4,030 

3,951 

_ 

Gold  . 

5,717 

5,640 

5,691 

Silver 

8,553 

8,658 

8,127 

Copper  . 

1 1,666 

10,802 

9,690 

Platinum 

8.815 

8,437 

8,079 

Iron 

16,822 

17,386 

15,48.3 

Iron  wire 

16,130 

16,728 

— 

Cast  steel 

16,357 

16,153 

I  5,709 

Steel  wire,  English 

15,470 

17,201 

16,394 

Steel  wire 

16,023 

16,443 

— 

570 


ACOUSTICS. 


In  September,  1831,  Mr.  Charles  Wheatstone  recorded  the  following  in  the 
“Journal  of  the  Royal  Institution:” 

“The  fact  of  the  transmission  of  sound  through  solid  bodies,  as  when  a 
stick  or  a  metal  rod  is  placed  at  one  extremity  to  the  ear  and  is  struck  or 
scratched  at  the  other  end,  did  not  escape  the  observation  of  the  ancient  phi¬ 
losophers  ;  but  it  was  for  a  long  time  erroneously  supposed  that  an  aeriform 
medium  was  alone  capable  of  receiving  sonorous  impressions,  and,  in  con¬ 
formity  with  this  opinion,  Lord  Bacon,  when  noticing  this  experiment,  assumes 
that  the  sound  is  propagated  by  spirits  contained  in  the  pores  of  the  body. 
The  first  correct  observations  on  this  subject  appear  to  have  been  made  by 
Dr.  Hooke,  in  1667,  who  made  an  experiment  with  an  extended  wire  of  suffi¬ 
cient  length  to  observe  that  the  sound  was  propagated  far  swifter  through  the 
wire  than  through  the  air.  Professor  Wunsch,  of  Berlin,  made,  in  1778,  a 
similar  experiment,  substituting  1,728  feet  of  wooden  laths  for  the  wire,  and 
confirmed  Dr.  Hooke’s  results.  Other  results  of  a  similar  nature  were  subse¬ 
quently  made  by  Herholt,  and  Rafn  Hassenfratz,  and  Gay  Lussac,  &c.;  but 
the  first  direct  observations  of  the  actual  velocity  of  sound  through  solid  con¬ 
ductors  were  made  by  Biot,  assisted  at  different  times  by  Bouvard  and  Martin. 
These  experiments  were  made  on  the  sides  of  the  iron  conduit-pipes  of  Paris 
through  the  length  of  951  metres  25  centimetres,  and  the  mean  result  of  two 
observations  made  in  different  ways  gave  3,459  metres,  or  11,090  feet,  per 
second  for  the  velocity  of  sound  in  cast  iron.  Previously  to  these  last-mentioned 
experiments,  Chladni  had  in  an  ingenious  manner  inferred  the  velocity  of 
sound  in  different  solid  substances,  and  his  results  are  fully  confirmed  by  cal¬ 
culations  from  other  grounds.  His  method  was  founded  on  Newton’s  demon¬ 
strations  that  sound  travels  through  a  space  of  a  given  length  filled  with  air 
in  the  same  time  that  a  column  of  air  of  the  same  length  contained  in  a  tube 
open  at  both  ends  makes  a  single  vibration.  His  discovery  of  the  longitudinal 
vibrations  of  solid  bodies,  which  are  exactly  analagous  to  the  ordinary  vibra¬ 
tions  of  columns  of  air,  enabled  him  to  apply  this  proposition  to  solid  bodies, 
and  to  establish  the  general  law  that  sound  is  propagated  through  an  elastic 
substance,  in  which  this  substance  makes  one  longitudinal  vibration.  In  this 
manner  he  ascertained  the  velocities  of  sound  in  the  following  substances 
among  others:  tin,  7,800;  silver,  9,300 ;  copper,  12,500;  glass  and  iron,  17,500; 
and  various  woods,  from  11,000  to  18,000  feet  in  a  second.  From  the  experi¬ 
ments  of  M.  Perotti  it  would  appear  that  the  intensity  .with  which  sound  is 
communicated  through  solid  matters  is  nearly  in  proportion  to  the  velocity  of 
its  transmission.  In  all  the  experiments  above  alluded  to  the  sounds  trans¬ 
mitted  were  either  mere  noises,  such  as  the  blow  of  a  hammer,  or,  as  in  Her¬ 
holt  and  Rafn’s  experiments,  a  single  musical  sound  produced  by  striking  a 
silver  spoon  attached  to  one  end  of  the  conducting-wire,  and  in  no  case  were 
any  means  employed  for  the  subsequent  augmentation  of  the  transmitted 
sound.  I  believe  that,  previously  to  the  experiments  which  I  commenced  in 
1820,  none  had  been  made  on  the  transmission  of  the  modulated  sounds  of 
musical  instruments,  nor  had  it  been  shown  that  sonorous  undulations  propa¬ 
gated  through  solid  linear  conductors  of  considerable  length  were  capable  of 
exciting  in  surfaces  with  which  they  were  in  connection,  a  quantity  of  vibra¬ 
tory  motion  sufficient  to  be  powerfully  audible  when  communicated  through 
the  air. 

“The  first  experiments  of  this  kind  which  I  made  were  publicly  exhibited 
in  1821,  and  notices  of  them  are  to  be  found  in  the  “  Literary  Gazette,” 


WHEATSTONE’S  EXPERIMENTS. 


57* 


“Ackerman’s  Repository,”  and  other  periodicals  of  that  year.  On  June  30, 
1823,  a  paper  of  mine  was  read  by  M.  Arago,  at  the  Academy  of  Sciences  at 
Paris,  in  which  I  mentioned  those  experiments  and  a  variety  of  others  relating 
to  the  passage  of  sound  through  rectilinear  conductors.  I  propose  in  the 
present  instance  to  give  a  more  complete  detail  of  these  experiments  than  I 
have  yet  published,  and,  at  the  same  time,  to  add  what  additional  facts  my 
subsequent  experience  has  furnished  me  with  on  the  same  subject. 

“Sonorous  bodies  are  audible  (the  extent  being  supposed  equal)  in  propor¬ 
tion  to  the  quantity  of  their  vibratory  surfaces.  Thus  a  plate  of  glass  or  metal 
is  capable  of  producing  powerful  sounds  without  accessory  means ;  but  the 
sound  of  vibrating  bodies  of  smaller  dimensions,  such  as  insulated  strings  or 
tuning-forks,  are  scarcely  audible  at  a  moderate  distance  from  the  ear,  but  the 
sounds  of  the  latter  are  capable  of  considerable  augmentation  when  commu¬ 
nicated  to  surlaces,  as  when  they  are  placed  to  a  table  or  the  sounding-board 
of  a  musical  instrument. 

“There  are  several  circumstances  which  influence  the  intensity  of  the  reso¬ 
nance  of  a  sounding-board ;  the  principal  of  these  is  the  plane  in  which  the 
vibrations  of  the  sounding  body  are  made  with  respect  to  the  reciprocating 
surface.  Thus  its  vibrations  may  be  so  communicated  as  to  be  perpendicular 
and  normal  to  the  surface  in  which  the  sound  is  the  greatest  augmented ;  or 
they  may  be  tangential  to,  or  in  the  same  plane  with,  the  surface  when  the 
sound  is  the  most  feeble.  The  first  of  the  causes  may  be  illustrated  by  placing 
a  vibratory  tuning-fork  perpendicular  to  the  surface  of  a  flat  board,  and  the 
second  by  placing  it  perpendicular  to  one  of  the  edges  of  the  board.  In  inter¬ 
mediate  positions,  viz.,  when  the  vibrations  are 
communicated  obliquely  to  the  surface,  the 
sound  will  be  found  to  have  intermediate  de¬ 
grees  of  intensity. 

“  These  facts,  which  the  extensive  investiga¬ 
tions  of  Savart  place  in  full  evidence,  being 
understood,  the  peculiarities  of  the  sounding- 
boards  of  various  musical  instruments  admit  of 
easy  explanation.  The  sounding-board  of  the 
pianoforte  is  better  disposed  than  that  of  any 
other  stringed  instrument,  as  the  planes  ot  the 
vibrations  of  the  strings  are,  on  account  of  the 
direction  in  which  they  are  struck  by  the  ham¬ 
mers,  always  perpendicular  to  its  surface.  The 
difference  of  intensity  when  a  string  vibrates  in 
this  way  and  when  it  vibrates  parallel  to  the 
surfaces  is  very  obvious,  and  may  be  easily  tried 
by  striking  it  with  the  finger  in  these  directions. 
There  is  no  other  instrument  now  in  use  in 
which  the  strings  make  their  vibrations  per¬ 
pendicular  to  the  sounding-board.  • 

“  Tuning-forks  are  the  most  convenient  in¬ 
struments  for  making  experiments  on  the  trans¬ 
mission  of  sound,  because  their  vibrations  are 
almost  inaudible  by  themselves,  and  only  be¬ 
come  strongly  audible  when  augmented  by  re¬ 
sonant  surfaces.  In  the  first  public  experiment 


SJUll 

am 


a 


Fig.  458. 


572 


ACOUSTICS. 


I  made,  in  1821,  the  reciprocating  instrument,  which  was  the  representation 
of  the  ancient  lyre,  was  so  constructed  as  to  produce  tangential  vibrations. 
The  tones  were  far  inferior  to  what  I  have  since  been  able  to  produce.  The 
transmitted  sounds  are  not  sensibly  impaired  when  the  wire  is  separated  at 
several  places  and  the  disunited  parts  fastened  together  by  mechanical  con¬ 
tact.  The  woodcut  (Fig.  458)  shows  the  arrangement. 

“  But  if  the  apparatus  be  intended  as  a  fixture,  it  will  be  easier  and  better 
to  use  one  piece  of  wire.  The  wire  consisted  of  four  portions  :  the  first 
touched  the  sounding-board  of  the  instrument  and  reached  half-way  to  the 
floor ;  the  second  passed  through  the  insulating-tube  in  the  floor,  and  termi¬ 
nated  in  the  ceiling  of  the  room  below  in  a  hook;  the  third  part  was  attached 
to  the  lyre  at  the  place  marked  at  the  dotted  end  of  the  line  on  the  sounding- 
board.  Each  of  the  parts  was  allowed  to  overlap  at  a  and  b ,  and  was  fastened 
by  means  of  a  screw-nut. 

“  The  sounds  of  an  instrument  may  be  at  the  same  time  transmitted  to 
more  places  than  one ;  for  instance,  communications  may  be  made  from  a 
square  pianoforte  to  a  resounding  instrument  above  and  to  another  below. 
In  a  similar  manner  the  sounds  of  an  entire  orchestra  may  be  transmitted, 
viz.,  by  connecting  the  end  of  the  wire  conductor  with  a  properly  constructed 
sounding-board,  so  placed  as  to  resound  to  all  the  instruments. 

“The  effect  of  an  experiment  of  this  kind  is  very  pleasing:  the  sounds, 
indeed,  have  so  little  intensity  as  scarcely  to  be  heard  at  a  distance  from  the 
reciprocating  instrument ;  but  on  placing  the  ear  close  to  it,  a  diminutive  band 
is  heard,  in  which  all  the  instruments  preserve  their  distinctive  qualities,  and 
pianos  and  fortes ,  crescendos  and  diminuendos ,  their  relative  contrasts.  Com¬ 
pared  with  an  ordinary  band  heard  at  a  distance  through  the  air,  the  effect  is 
as  a  landscape  seen  in  miniature  beauty  through  a  concave  lens  as  compared 
with  the  same  view  viewed  by  the  ordinary  vision  through  a  murky  atmo¬ 
sphere. 

“In  the  preceding  experiments  on  the  transmission  of  sound  through  solid 
bodies  the  conductors  have  been  represented  as  straight ;  but,  though  sound 
is  transmitted  the  more  readily  through  straight  conductors,  it  will  yet  pass, 
though  with  diminished  intensity,  through  rods  with  angular  and  curved 
bendings.  If  a  vibrating  tuning-fork  be  placed  at  one  end  of  a  straight  brass 
rod,  the  other  end  of  which  rests  perpendicularly  upon  a  sounding-board,  the 
vibrations  will,  in  accordance  with  what  has  been  above  stated,  be  powerfully 
transmitted.  On  gradually  bending  the  red  at  any  part  of  its  length,  while 
the  vibrations  of  the  tuning-fork  are  kept  in  the  same  plane  with  the  angle  of 
the  bent  rod,  the  transmitted  sound  will  progressively  decrease  in  intensity,' 
and  will  become  very  feeble  when  the  angle  becomes  a  right  one:  as  the 
bending  is  continued,  so  as  to  make  the  angle  between  the  two  parts  of  the 
rod  more  acute,  the  intensity  of  the  sound  will  increase  in  the  same  order  in 
which  it  had  before  diminished,  and  when  the  two  parts  of  the  rod  are  nearly 
parallel,  the  sound  will  be  nearly  as  loud  as  when  the  transmission  was  recti¬ 
linear.  If,  during  the  gradual  bending  of  the  rod,  the  plane  of  the  vibrations 
of  the  tuning-fork  be  perpendicular  to  the  plane  of  the  angle  made  by  the  two 
parts  of  the  rod,  the  same  changes  will  be  observed,  but  in  a  more  obvious 
manner  than  in  the  former  case ;  and  when  the  angle  becomes  a  right  one,  the 
sound  will  be  scarcely  perceptible.  At  intermediate  inclinations  of  the  two 
planes  the  gradations  of  intensity  occasioned  by  the  bending  of  the  rod  wall 
be  found  to  be  intermediate.  The  changes  of  intensity  dependent  on  the 


TRANSMISSION  OF  SOUNDS. 


573 


variation  of  the  angles  of  the  two  planes  may  be  instructively  shown  by  bend¬ 
ing  the  rod  permanently  to  a  right  angle,  and  placing,  as  before,  the  stem  of  a 
tuning-fork  so  as  to  form  the  prolongation  of  one  of  the  parts  of  the  rod,  the 
other  part  of  the  rod  resting  on  the  sounding-board.  On  gradually  turning 
the  tuning-fork  round  the  axis  of  its  stem,  without  inclining  it  to  the  rod,  the 
plane  of  the  vibrations  will  assume  every  angle  with  respect  to  the  plane  in 
which  the  two  parts  of  the  rod  are  bent.  During  the  revolution  it  will  be 
observed  that  when  the  planes  coincide  the  intensity  will  be  at  its  maximum; 
and  when  they  are  perpendicular  to  each  other,  at  its  minimum.  Thus,  sup¬ 
posing  the  sound  to  commence  when  the  two  planes  are  parallel,  it  will  gra¬ 
dually  diminish  until  they  make  an  angle  of  90°;  it  will  then  increase  in  the 
same  changes  of  intensity  in  an  inverted  order,  until  it  acquires  its  maximum 
at  1800;  it  will  again  decrease  between  this  and  270°,  and  increase  until  it 
arrives  at  its  first  position  0°. 

“  If  the  stem  of  the  tuning-fork  be  placed  perpendicularly  on  the  side  of 
a  conducting-rod  resting  on  a  sounding-board,  the  same  phenomena  may  be 
observed ;  the  stem  of  the  tuning-fork  is,  in  fact,  a  short  conductor,  forming  a 
right  angle  with  the  rod.  Were  it  necessary  for  the  transmission  of  sound 
that  the  undulations  should  propagate  themselves  rectilinearly,  it  is  obvious 
that  they  would  not  pass  through  a  bent  rod;  and,  on  the  other  hand,  had 
they  the  property  of  diffusing  themselves  equally  in  all  directions,  we  should 
not  observe  any  difference  of  intensity  in  the  experiments  above  noticed. 

“  These  experiments  lead  us  to  conclude  that  sound  diffuses  itself  in  all 
directions,  though  unequally;  that  it  is  communicated  more  readily  in  the 
plane  in  which  the  original  vibrations  are  made,  and  that  the  greatest  degree 
of  intensity  is  in  the  direction  of  these  vibrations. 

“  To  extend  these  experiments  much  further  would  be  attended  with  some 
difficulties;  but,  as  the  velocity  of  sound  is  much  greater  in  solid  substances 
than  in  air,  it  is  not  improbable  that  the  transmission  of  sound  through  solid 
conductors  and  its  subsequent  reciprocation  may  hereafter  be  applied  to  many 
useful  purposes.  Sound  travels  through  the  air  at  the  rate  of  1,142  feet  per 
second;  but  it  is  communicated  through  iron  wire,  glass,  cane,  or  deal  wood 
rods  with  the  velocity  of  about  18,000  feet  per  second,  so  that  it  would  travel 
the  distance  of  200  miles  in  less  than  a  minute. 

“When  sound  is  allowed  to  diffuse  itself  in  all  directions  as  from  a  centre, 
its  intensity,  according  to  theory,  decreases  as  the  square  of  the  distance  in¬ 
creases;  but,  if  it  be  confined  to  one  rectilinear  direction,  no  diminution  of 
intensity  ought  to  take  place ;  but  this  is  on  the  supposition  that  the  conducting 
body  possesses  perfect  homogeneity  and  is  uniform  in  its  structure, — conditions 
which  never  obtain  in  our  actual  experiments.  Could  any  conducting  sub¬ 
stance  be  rendered  perfectly  equal  in  density  and  elasticity,  so  as  to  allow  the 
undulations  to  proceed  with  a  uniform  velocity  without  any  reflections  or  inter¬ 
ferences,  it  would  be  as  easy  to  transmit  sounds  through  such  conductors  from 
Aberdeen  to  London  as  it  is  now  to  establish  a  communication  from  one 
chamber  to  another.  Whether  any  substance  can  be  rendered  thus  homo¬ 
geneous  and  uniform  remains  for  future  philosophers  to  determine.” 

At  the  Polytechnic  Sir  Charles  Wheatstone  very  kindly  superintended  the 
arrangements  of  the  rods  passing  through  various  apartments  from  the  base¬ 
ment  to  the  lecture-room,  and  subsequently  had  the  pleasure  of  seeing  the 
manner  in  which  his  beautiful  experiments  with  four  instruments  and  the 
sounding-boards  of  four  harps,  called  the  “telephonic  concert,”  were  appre- 


574 


ACOUSTICS. 


dated  by  Her  Majesty,  the  late  lamented  Prince  Consort,  H.R.H.  the  Prince 
of  Wales,  and  the  >ounger  members  of  the  Royal  Family. 

The  efforts  made  by  the  writer  to  give  refined  science  at  the  Polytechnic  to 
the  public  at  that  time  were  net  successful  in  a  monetary  point  of  view,  and 
he  lost  his  private  patrimony  trying  to  effect  this  object,  as  sole  proprietor  of 
that  establishment.  Grown  wiser  by  experience,  he  is  obliged  to  cater  differ¬ 
ently,  and  the  institution  has  flourished  and  is  now  most  prosperous,  and  the 
author  hopes,  with  the  blessing  of  the  Highest,  it  may  long  continue  to  be  so. 

A  very  pretty 
illustration  of 
Wheatstone’s  ex¬ 
periments  with 
the  transmission 
of  vibrations 
through  solid  con¬ 
ductors  may  be 
performed  by  con¬ 
structing  a  series 
of  boxes  (a,  Fig. 
459)  to  fit  one 
within  the  other, 
the  last  to  contain 
a  musical  box 
resting  on  a  few 
folds  of  baize. 
The  latter,  whilst 
playing,  is  shut  up 
in  the  other  boxes, 
and  the  sound 
gradually  dies 
away  ;  it  is,  how¬ 
ever,  immediately  brought  back  into  the  room  by  thrusting  a  long  wooden 
rod  through  the  holes  made  in  the  boxes,  and,  of  course,  superimposed  upon 
each  other.  Directly  the  end  of  the  rod  touches  the  musical  box,  the  hand 
instantly  feels  the  vibrations,  and  the  sound  is  now  partially  heard,  becom¬ 
ing  quite  loud  when  the  sounding  board  of  a  violin,  or,  better  still,  that  of 
a  harp  lute  (b,  Fig.  459),  is  pressed  lightly  down  on  the  end  of  the  wooden 
rod. 

Gas  and  water  are  supplied  to  our  dwellings,  and  may  be  turned  on  or  off 
at  pleasure  ;  so  it  is  with  the  musical  sounds, —  they  become  audible  or  in¬ 
audible  as  the  sounding-board  is  applied  or  removed. 

The  “  telephone,”  an  instrument  for  transmitting  instrumental  and  vocal 
sounds  by  the  telegraph  wire,  is  another  wonderful  modern  application  of 
science  ;  and  though  the  transmission  of  a  song  might  not  be  very  useful,  an 
affidavit  viva  voce ,  sent  through  hundreds  of  miles,  may  be  found  important 
in  some  future  cause  celebre.  The  telephone  is  described  in  connection  with 
Wheatstone’s  telegraph  apparatus,  page  464. 

Whilst  alluding  to  ingenious  and  pleasing  acoustic  experiments,  it  may  be 
well  to  mention  here  the  very  prettv  toy  called  “  The  Piping  Bullfinch,”  which 
was  so  much  admired  in  the  Swiss  Court  of  the  great  London  Exhibition  of 
1862.  When  a  spring  is  touched,  a  little  model  of  a  bullfinch,  with  feathers. 


Fig.  459. — The  Miniature  Telephonic  Concert. 

B,  stick  passed  through  the  boxes  A,  and  touching  the  musical  box  at  one  end, 
whilst  the  other  is  pressed  against  the  sounding-board  of  some  instrument. 


TRANSMISSION-  OF  SOUNDS. 


Sr  5 


Fig.  460. —  The  Enlarged  Model  of  the  interior  of  the  Mechanism  called 

the  Piping  Bullfinch, 

The  motion  being  produced  by  an  endless  screw,  turned  by  the  hand  instead  of  by  clockwork,  as  in  the 

Piping  Bullfinch  toy. 

moving  wings,  and  beak,  pops  out  of  the  box,  and  pipes  almost  as  naturally  as 
a  living  songster. 

The  listener  imagines  that  the  sound  comes  from  the  beak  and  from  the 
body  of  the  bird;  but  that  is  not  the  case:  the  box  would  sing  just  as  well 
without  the  bird  as  with  it— the  bird  serves  to  engage  the  eye,  the  music  the 
ear.  The  sound  comes  from  a  small  pipe,  provided  with  a  piston,  which  con¬ 
tinually  shortens  and  lengthens  the  tube.  The  action  of  the  piston  is  secured 
by  a  lever,  which  is  moved  as  the  studs  of  a  barrel  (like  a  barrel  organ)  come 
round  and  touch  it.  A  regular  piping  tune  is  set  out  in  studs  on  the  barrel, 
and  the  pipe  which  emits  the  sound  is  exactly  like  the  pipes  sold  in  the  streets, 
only  instead  of  the  column  being  shortened  and  lengthened  by  immersion  in 
water,  it  is  done  with  a  piston,  and  the  pipe  supplied  with  air  from  a  small 
bellows. 


Fig.  461 Portrait  and  Signature  of  Faraday. 

The  former  from  a  photograph  by  Mr.  James  How. 


CHEMISTRY. 


THE  son  of  a  smith— the  apprentice  of  a  bookseller  and  bookbinder  in 
Blandford  Street,  Manchester  Square—a  journeyman  at  some  other 
place  of  business—and  subsequently  engaged  by  Sir  Humphrey  Davy  at 
weekly  wages— no  lordly  patronage  heralded  the  approach  of  Faraday:  he 
was  indebted  to  no  one  except  another  scientific  man,  like  himself  an  humble 
beginner — a  chemist’s  apprentice,  a  washer  of  bottles.  And  yet  he  lived  to 
make  a  name  that  few  have  or  will  ever  be  able  to  achieve.  What  does  he 
say  of  himself? 


CHEMISTRY. 


577 


“  I  was  formerly  a  bookseller  and  binder,  but  am  now  turned  ‘ philosopher' 
which  happened  thus  :  whilst  an  apprentice,  I  for  amusement  learned  a  little 
chemistry  and  other  parts  of  philosophy,  and  felt  an  earnest  desire  to  proceed 
in  that  way  further.  After  being  a  journeyman  for  six  months  under  a  dis¬ 
agreeable  master,  I  gave  up  my  business,  and  through  the  interest  of  one  Sir 
H.  Davy  filled  the  situation  of  chemical  assistant  to  the  Royal  Institution  of 
Great  Britain,  in  which  office  I  now  remain,  and  where  I  am  constantly  em¬ 
ployed  in  observing  the  works  of  Nature,  and  tracing  the  manner  in  which  she 
directs  the  order  and  arrangement  of  the  world.”* 

On  the  1 8th  March,  1813,  it  was  resolved  “  That  Micha.l  Faraday  be  en¬ 
gaged  to  fill  the  situation  lately  occupied  by  Mr.  Payne,  on  the  same  terms.” 

Faraday  accompanied  Sir  H.  Davy  to  Rome,  and  was  re-engaged  by  the 
Royal  Institution  managers  on  the  15th  May,  1815  ;  and  as  his  first  private 
and  original  sacrifices  of  time,  energy,  and  talent  were  made  to  “Chemistry,” 
his  portrait  is  placed  at  the  head  of  this  section. 

What  income  Faraday  derived  from  the  Royal  Institution  is  not  exactly 
known.  The  writer  has  heard  the  late  Mr.  Robert  Murray  say  that  he  had 
only  £ 200  per  annum,  and  apartments,  for  a  very  long  period  ;  until  some¬ 
body  suggested  that  he  was  no  longer  an  assistant,  but  a  “master,”  and  ought 
to  be  paid  as  a  “philosopher.”  Much  or  little,  it  affected  not  Faraday:  his 
private  charities  and  good  deeds  are  known  only  to  the  Great  Giver  of  all 
things. 

The  “  Mechanic’s  Magazine,”  speaking  in  the  hearty  truthfulness  of  inde¬ 
pendent  journalism,  said,  in  October,  1859,  that  which  carried  conviction  to 
the  hearts  of  many  who  see  how  often  sc  e  ice  is  degraded  into  “  flunkeyism,” 
instead  of  being  elevated  to  “  Faradism,’ — 

“  The  other  characteristic  of  our  time  to  which  we  refer  is  its  boldness,  com¬ 
prehensiveness,  and  certainty  of  mental  inquiry,  which  expresses  itself  in  its 
favourite  term — science.  We  had  a  notable  example  of  this  in  the  speech  of 
the  Prince  Consort  at  Aberdeen,  which  we  reprinted  in  our  journal  a  fortnight 
ago.  It  was  a  fine  specimen  of  the  best  mind  among  us.  What  choice,  pure 
English  the  language  was,  and  of  such  delicate  precision  and  beauty!  What 
graceful  personal  modesty  the  speaker  showed!  How  full  the  discourse  was 
of  the  old  German  solidity  and  seriousness  of  purpose,  that  marks  all  the 
German  people,  whether  in  the  old  Fatherland  or  in  Angleland.  The  term 
‘science’  in  this  address  is  made  to  embrace  the  whole  range  of  the  human 
mind.  There  are  three  objects  of  man’s  contemplation  and  inquiry — Nature, 
Man,  God.  The  human  mind  has  two  methods  of  working — analysis  and 
synthesis.  It  dissects  into  parts,  observes,  examines, reasons  about  each  part; 
or  intuitively  it  grasps  the  law  that  binds  and  controls  the  parts  and  knits  them 
into  a  whole.  All  follow  this  method,  says  the  Prince — the  child,  the  man  of 
mere  practical  instinct,  or  the  philosopher.  The  child,  as  soon  as  his  first 
surprise  and  ecstacy  at  the  new  universe  subside  a  little,  begins  to  ask  the  how 
and  why  of  things.  He  practises  his  analysis  by  pulling  his  toy  to  pieces  to 
discover  how  it  works  ;  or  he  performs  a  splendid  generalization  ;  as,  for  ex¬ 
ample,  when  the  fire  burns  him,  he  affirms  to  himself  that  fire  burns  in  every 
instance,  at  all  places  and  times,  though  he  has  only  experienced  one  instance 
of  its  burning  power.  The  practical  man  is  instinctively  impelled  to  philoso¬ 
phize,  in  his  rough,  homespun  method,  on  the  facts  he  is  brought  into  contact 


♦Tyndall  ‘‘On  Faraday  as  a  Disco*  erer.” 

37 


578 


CHEMISTR  K 


with.  But  the  philosopher,  by  stronger  instinct  and  by  conscious  self-deter¬ 
mination,  directs  his  eye  to  every  part  of  the  great  All. 

“  Science,  the  Prince  hints,  has  been  of  slow  growth  in  England,  partly  be¬ 
cause  we  English  are  so  wedded  to  what  is  immediately  useful,  what  immediately 
shows  a  return  in  pounds,  shillings,  and  pence  ;  and  partly  from  our  excessive 
devotion  to  antiquity,  that  4  till  of  late  has  almost  systematically  excluded 
from  our  school  and  university  education’  the  great  subjects  and  the  results 
of  modern  inquiry,  while  it  has  given  to  antique  things  that  liveliness  of  interest 
we  feel  all  through  life  in  the  subjects  we  studied  in  early  years. 

“  The  illustrious  speaker  lays  great  stress  on  the  absence  of  all professionalism 
and  officialism  from  science.  Knowledge ,  in  his  eyes ,  has  no  aristocracy  or 
priesthood.  Its  genuine  students  are  not  ‘  a  secret  confraternity  of  men 
jealously  guarding  the  mysteries  of  their  profession f  their  activity  is  ‘the 
republican  activity  of  the  Roman  Forum.’  But  if  boldness  and  freedom,  the 
Prince  reminds  us,  are  the  characteristics  of  the  philosopher,  equally  so  is  re¬ 
verence.  The  more  he  explores  the  more  he  becomes  aware  of  4  the  boundless¬ 
ness  of  the  universe ,  whose  confines  appear  ever  to  retreat  before  our  finite 
minds?  True  thinkers  are  4  not  conceited  pedants ,  wrapped  up  in  their  own 
mysterious  importance ,  but  humble  inquirers  after  truth ;  not  God-defying 
Titans ,  but  reverent ,  pious  pilgrims  towards  a  Holy  Land — God's  truth  — 
God's  laws ,  as  manifested  in  His  works ,  in  His  creation?” 

The  imponderable  forces  have  already  been  dealt  with,  and  yet  there  remain 
those  of  Gravitation,  Cohesion,  Adhesion,  and  Chemical  Action.  To  speak 
of  the  first  would  be  to  enter  upon  the  science  of  astronomy,  which  is  impos¬ 
sible  in  this  work;  it  is  sufficient  to  refer  the  reader  to  the  first  lines  of  the 
epitaph  under  the  statue  of  Sir  Isaac  Newton: 

HERE  LIES  INTERRED 
ISAAC  NEWTON,  KNIGHT, 

WHO, 

WITH  AN  ENERGY  OF  MIND  ALMOST  DIVINE, 

GUIDED  BY  THE  LIGHT  OF  MATHEMATICS  PURELY  HIS  OWN, 

FIRST  DEMONSTRATED 

TIIE  MOTIONS  AND  FIGURES  OF  THE  PLANETS, 

THE  PATHS  OF  THE  COMETS, 

AND  THE  CAUSES  OF  THE  TIDES- 

The  reader  working  out  only  the  philosophy  of  the  last  lines  will  soon  acquire 
a  knowledge  of  the  power  supposed  to  exist,  and  which  by  universal  consent  is 
called  Gravitation. 

Newton  was  born  on  the  25th  December,  1642,  and  died  on  the  20th  March, 
1726.  Gravity  is  defined  as  that  force  which  tends  to  make  bodies  move 
downwards  towards  the  centre  of  the  earth,  and  which  prevents  their  being 
moved  upwards.  If  the  atmosphere  surrounding  our  earth  were  not  fixed  to 
it  by  the  invisible  chain  of  gravitation,  it  would  have  expanded  long  ago  into 
space,  and  no  human  beings  with  their  present  organization  would  have  been 
left  to  tell  the  tale  of  desertion,  for  all  would  have  perished  for  want  of  air. 

The  amount  of  downward  force  which  causes  a  body  to  gravitate  to  the 
earth  is  called  its  “weight.” 

For  the  sake  of  comparison  it  was  found  necessary  to  fix  some  “standard” 
to  which  the  weights  of  different  substances  might  be  teferred. 

Water  was  selected,  because  it  is  to  be  found  in  all  places  and  in  all  sea¬ 
sons:  its  presence  is,  in  fact,  universal;  and  therefore  a  pound  avoirdupoi- 
of  water,  containing  7,000  grains,  of  which  each  252^ 58  grains  are  equal  to 


COHESION. 


579 


one  cubic  inch,  is  taken  as  the  fixed  and  determined  standard, — provided  al¬ 
ways  that  it  be  estimated  at  a  temperature  of  62°  F.,  the  barometer  being  at 
30  inches. 

As  water  is  taken  as  the  standard  for  the  determination  of  the  specific  gra¬ 
vity  of  solids  and  liquids,  so  air  at  62°  F.  and  30  in.  barometer  is  taken  for  that 
of  all  gaseous  bodies. 

The  mode  of  determining  the  specific  gravity  of  solids  is  very  simple: 

1 .  Weigh  the  solid  substance  in  air; 

2.  Also  in  water,  taking  care  to  prevent  air-bubbles  adhering  to  the  sub¬ 
stance;  and  this  the  writer  finds  is  entirely  pre/ented  (where  the  substance 
is  insoluble  in  alcohol)  by  dipping  the  solid  into  alcohol,  and  then  into  several 
waters,  at  last  placing  it  in  the  vessel  of  water  in  which  the  specific  gravity  is 
to  be  ascertained. 

3.  Divide  the  gross  weight  by  the  loss  of  weight  of  water,  and  the  quotient 
gives  the  specific  gravity. 

The  specific  gravity  of  liquids  is  ascertained  directly  by  first  adjusting  a 
glass  bottle  (the  weight  of  which  is  balanced  by  a  counterpoise)  to  hold  i,ooo 
grains:  if  the  same  bottle  be  filled  with  alcohol,  it  weighs  less  than  water, 
viz.,  792  grains;  if  filled  with  oil  of  vitriol,  it  weighs  more  than  the  same  bulk 
of  water,  viz.,  1,845  grains.  The  exact  weight  is  the  reading,  and  no  calcula¬ 
tion  is  required. 

The  determination  of  the  specific  gravity  of  a  gas  is  founded  on  the  same 
principles,  but  the  most  elaborate  precautions  must  be  taken.  A  given  volume 
of  air,  such  as  that  contained  in  a  wine-flask,  is  first  weighed  ;  then  it  is 
emptied  by  the  air-pump  and  weighed  again ;  lastly,  it  is  weighed  full  of  the 
gas  of  which  it  is  required  to  ascertain  the  specific  gravity.  A  simple  rule-of- 
three  sum  determines  the  question — that  is,  roughly:  to  perform  the  experi¬ 
ment  accurately,  the  precautions  insisted  on  by  Regnault  (“Annals  de  Chemie,” 
III.,  xiv.  21 1)  must  be  taken. 

Daniell  defines  cohesion  to  be  homogeneous  attraction:  l/ios  like,  and  ye  Vos 
kind — alike  in  nature  of  properties.  Two  surfaces  of  lead  cohere,  provided 
that  they  are  perfectly  clean  and  bright;  two  bars  of  iron  sufficiently  heated 
may  be  welded  together  by  hammering  or  any  other  kind  of  mechanical  pres¬ 
sure  or  force.  If  metallic  contact  between  the  two  bars  be  not  well  secured 
by  proper  handicraft,  the  weld  is  imperfect,  and  the  two  surfaces  of  iron  do 
not  cohere,  but  separate  on  the  application  of  slight  mechanical  force.  A  drop 
of  dew  on  a  cabbage-leaf  is  an  excellent  illustration  of  cohesive  power  in  a 
liquid ;  and  this  property  has  been  turned  to  a  good  account  by  Professor 
Tomlinson,  and  subsequently  by  Dr.  Moffat,  of  Glasgow,  who  has  quite  dig¬ 
nified  an  otherwise  humble  department  of  phys  cal  iruth  by  his  efforts  to  make 
the  new  art  of  Oleography  popular. 

These  oleographs  (Fig.  462)  indicate  special  figures  always  assumed  by  any 
particles  of  oil  or  other  fluids  of  a  kindred  nature;  therefore  they  become  guides 
to  direct  the  analyst,  who,  by  consulting  these  figures,  can  ascertain  whether 
the  oil,  tallow,  lard,  or  other  kind  of  grease  is  really  what  it  purports  to  be. 

Professor  Tomlinson  was  the  first  to  call  attention  to  this  peculiar  class  of 
experiments,  and  his  original  discoveries  have  been  greatly  CNtended  by  Dr. 
R.  Carter,  Moffat  Lecturer  on  Chemistry,  Glasgow,  to  whom  the  writer  is 
indebted  for  the  originals  from  which  the  cuts  (Fig.  462)  are  taken.  The 
latter  gentleman's  paper  in  the  “Chemical  News”  (Vol.  XVI II.,  No.  473)  is 
so  very  concise  and  explanatory  of  the  whole  process,  that  it  is  given  here 

37 — 2 


58° 


CHEMISTRY. 


nearly  in  extenso.  The  process  will  remind  the  reader  of  the  art  of  marbling 
paper,  which,  like  the  oleographic  process,  is  one  of  the  most  ingenious  and 
amusing  that  can  be  introduced  to  a  general  audience. 


Fig.  462, —  Oleographs  of  Tallow  and  Lard ,  taken  by  Dr.  Moffat 

Oleography:  being  a  Process  for  the  Utilization  of 
Tomlinson’s  Cohesion  Figures. 

“  Chemists  are  aware  that  most  kinds  of  oil  when  poured  on  water  spread 
over  its  surface,  and  sooner  or  later  break  into  variegated  patterns,  some  of 
which  are  of  great  beauty.  When  we  make  a  few  experiments  in  this  direction, 
attention  is  attracted  to  the  regularity  of  the  forms  assumed,  and  further,  that 
almost  all  the  common  oils  give  different  models  of  patchwork  according  to 
the  length  of  time  that  the  oils  are  exposed.  Experiments  conducted  in  my 
laboratory  show  that  from  the  construction  of  the  oil-film  we  can  with  consi¬ 
derable  certainty  determine  the  kind  of  oil  examined,  and  also  its  genuineness. 
A  drop  of  pure  sperm  oil  let  fall  on  a  basin  or  plate  full  of  water  quickly  be¬ 
comes  an  enlarged  circular  film  of  several  inches  diameter,  breaking  up  near 
the  edges  into  small  round  holes.  This  takes  place  in  about  sixty  seconds  in 
the  case  of  pure  sperm.  The  centre  of  the  patch  is  at  the  same  time  filled 
with  little  holes,  somewhat  smaller  than  those  at  the  edges.  At  two  minutes 
till  the  little  openings  are  considerably  expanded,  and  they  continue  to  extend 
until  after  a  lapse  of  thirty  minutes  or  so,  when  the  oil  is  broken  up  and 
detached.  There  is  value  attached  to  this  simple  test.  Green  rape  oil  breaks  up 
slowly,  more  so  than  sperm ;  but  after  sixty  seconds  its  pattern  is  different, 
the  circles  being  large  and  beautifully  defined.  Purified  rape  oil  becomes 
much  larger  in  the  pattern  circles  than  green  rape  in  the  same  time.  Lucca 
olive  gives  in  one  minute  a  large  representation,  in  two  minutes  an  extra¬ 
ordinary  development,  and  in  three  minutes  a  very  large  likeness. 

“  Green  olive,  on  the  other  hand,  gives  but  a  small  pattern  in  one  minute, 
and  conducts  itself  quite  at  variance  with  Lucca  olive.  Again,  seal  and 
castor  oil  give  forms  which  are  very  small  compared  with  many  oils.  In 
making  these  observations  it  is  necessary  to  attend  to  the  size  of  the  drop  of 
oil,  the  height  it  falls,  the  force  with  which  it  does  so,  the  perfect  purity  of  the 


OLEOGRAPHY 


5»i 


cold  water,  and  the  stillness  of  the  water  at  the  time.  To  make  the  experi¬ 
ment,  proceed  as  follows  :  From  a  small  dry  burette  drawn  out  to  a  fine  point, 
filled  up  to  a  certain  mark  with  the  oil,  cautiously  let  fall  a  single  drop  at  four 
inches  height  upon  the  centre  of  the  water  contained  in  a  common  soup-plate 
or  glass  basin.  We  shall  assume  that  Lucca  olive  is  taken.  The  drop  should 
at  once  spread  about  four  inches  on  the  water  circularly.  If  it  does  not  do  so 
at  once,  then  the  plate  or  the  water  is  not  clean,  and  the  water  is  to  be  poured 
out,  the  plate  well  washed  with  water,  and  again  filled.  All  rubbing  with 
towels  is  to  be  avoided.  At  thirty  seconds  the  appearance  of  the  representa¬ 
tion  is  very  lovely,  having  all  the  similitude  of  crochet-work.  To  give  defini¬ 
tions  of  its  many  figures,  I  would  need  to  have  Roget's  ‘Thesaurus of  English 
Words  and  Phrases’  before  me.  It  is  needless  at  present  to  enumerate  the 
diversity  of  these  oil-films  at  different  periods  of  time.  Tomlinson  has  enriched 
science  by  his  masterly  descriptions  of  them.  He  has  done  more  in  this 
department  than  any  man.  To  him  is  due  many  discoveries  in  experimental 
philosophy — facts  of  the  greatest  value  and  importance.  It  is  to  him  that  I 
would  ascribe  my  recent  discovery  of  the  -utilization  of  the  cohesion  figures  of 
oil  on  water.  Had  it  not  been  fora  knowledge  of  the  facts  connected  with  his 
researches  in  this  beautiful  and  interesting  department  of  science,  then  in  all 
probability  the  oil  figures  would  have  remained  what  they  are — beautiful  to 
look  at,  but  transient  in  the  extreme.  The  eye  becomes  tutored  and  experienced 
to  these  forms,  so  that  it  can  readily  determine  the  kind  of  oil  under  examina¬ 
tion.  I  do  not  aver  this  to  be  the  fact  in  all  cases.  In  very  many  instances 
it  is  so.  Indeed,  in  all  that  have  ccme  under  my  notice  this  is  the  conclusion 
arrived  at.  Perfect  concordance  of  results  is,  I  am  almost  certain,  to  be 
obtained  when  the  size  of  the  diop  of  oil  and  all  other  points  are  rigidly 
attended  to.  A  slight  tremor  or  shaking  of  the  water  is  detrimental  to  a 
perfect  pattern.  I  have  noticed  that  even  a  person  coughing  near  the  oil-film 
deranges  its  conformation. 

“Those  who  have  watched  these  exquisite  shapes  have  often  wished  to 
secure  them  on  paper  as  a  kind  of  photograph,— to  have  them  brought  before 
the  eye  palpable  and  fixed,  to  be  seen  at  once  a  reality,  a  permanent  image. 
Many  have  tried  to  do  so.  For  long  I  had  attempted  to  do  the  same.  In  many 
things  apparently  difficult,  yet  really  simple,  we  see  only  that  which  appears  to 
be  insurmountable.  It  is  in  their  very  simplicity,  however,  that  we  fail  to  grasp 
the  solution  of  the  problem.  The  oil  patterns  uninjured  can  as  readily  be  trans¬ 
ferred  from  the  surface  of  water,  and  permanently  fixed  to  be  placed  in  our  al¬ 
bums,  as  we  can  pour  water  from  one  vessel  to  another.  N  o  matter  what  colours 
we  desire,  we  can  obtain  them  of  any  hue  we  please.  They  rival  the  most  beau¬ 
tiful  photographs.  The  faintest  tracery  is  brought  out  with  the  most  perfect 
fidelity.  Two  well-known  photographers  of  this  city,  to  whom  I  showed  them 
this  week,  declared  they  were  excellent  photographs ;  and  yet  not  a  trace  of  the 
chemicals  photographers  use  was  employed.  The  process  can  be  described 
in  three  lines:  Obtain  the  oil  pattern,  note  the  time,  lay  a  piece  of  glazed- 
surface  paper  on  the  pattern  for  an  instant,  take  it  off,  place  on  the  surface  of 
a  piate  of  ink  for  a  moment,  remove  and  wash  off  the  excess  of  ink  with 
water,  and  your  pattern  is  there  as  it  was  on  the  water.  You  now  have  an 
exquisite  representation  in  black,  as  fine  as  any  photograph.  A  scarlet  is 
obtained  by  employing  a  solution  of  cochineal  or  any  of  the  scarlet  coal-tar 
colours.  We  have  them  in  orange,  red,  scarlet,  black,  blue,  and  other  tints. 
A  good  result  is  got  by  first  passing  the  paper  containing  the  pattern  of  oil 


5§2 


CHEMISTR  Y 


through  ink,  and  then  through  cochineal.  The  principle  of  the  matter  is  this : 
the  paper  absorbs  the  oil  at  the  several  parts,  to  the  exclusion  of  the  water. 
The  ink  colours  the  water  parts,  but  at  the  same  time  tints  the  oil  parts  very 
faintly,  which  gives  it  the  appearance  of  relievo.  Any  kind  of  paper  almost 
will  do.  Tissue,  green,  glazed,  white,  &c.,  give  pretty  good  results.  The  paper 
I  employ,  which  I  find  to  take  up  the  most  delicate  parts,  is  what  is  known  as 
white-surface  paper  (glazed  on  one  side  only).  We  get  it  cut  in  circular  pieces 
of  about  four  inches  in  diameter.  A  larger  pattern  could  readily  be  obtained 
by  using  a  larger  drop  of  oil  and  a  larger  size  of  paper. 

“We  have  been  able  to  take  perfect  facsimiles  of  fern-leaves  by  coating 
them  with  oil,  placing  them  on  the  glazed  paper,  pressing  them  against  the 
paper,  obtaining  a  perfect  likeness  of  the  fern,  and  showing  it  in  relief  by  draw¬ 
ing  the  paper  through  ink,  or  cochineal,  or  other  colour.  In  printing  with 
oiled  types  on  the  paper  and  colouring  aftenvards,  we  have  also  been  able  to 
get  beautiful  results.  I  think  that  paper-stainers  and  paperhanging  manufac¬ 
turers  might  be  greatly  benefited  by  paying  attention  to  our  method. 

“  I  confidently  hope  to  be  able  to  transfer  the  patterns  even  to  cloth,  to 
stone,  &c. 

“  Scientific  chemists  are,  of  course,  only  interested  in  this  process  so  far  as 
a  test  for  the  purity  of  oils.  I  have  made  many  hundreds  of  experiments  with 
the  process,  and  in  a  large  number  of  instances  have  got  results  with  mixtures 
of  oils  differing  very  materially  from  those  with  genuine  oils.  Many  more 
experiments  are  needed  to  confirm  this,  and  in  a  work  on  the  detection  of  oils, 
on  which  I  am  at  present  engaged,  having  added  a  large  number  of  reliable 
tests,  this  will  be  very  fully  gone  into.” 

Since  the  above  was  written,  Mr.  Woodward,  Lecturer  on  Chemistry,  Mid¬ 
land  Institution,  Birmingham,  has  described  in  the  same  valuable  scientific 
journal  the  following  method  of  , 

Exhibiting  Cohesion  Figures  to  a  Lecture  Audience. 

“  Wishingto  exhibit  the  singular  figures  discovered  by  Professor  Tomlinson 
and  known  as  cohesion  figures,  I  proposed  adopting  the  method  men  ioned 
by  Mr.  Reynolds  in  the  ‘  Chemical  News’  of  November  27th  ;  but  it  occurred 
to  me  that  an  arrangement  similar  to  that  used  to  show  waves  in  water  would 
probably  serve  the  purpose.  1  therefore  tried  the  following  plan,  which,  though 
not  so  successful  as  the  one  I  shall  afterwards  describe,  is  well  worth  trying : 

“A  box  with  a  glass  bottom  was  filled  with  water,  and  the  lime-light  placed 
underneath  the  box.  On  throwing  a  spot  of  liquid,  giving  a  cohesion  figure, 
on  to  the  water,  the  figure,  more  or  less  definite,  was  exhibited  on  a  tracing- 
paper  screen  placed  above  the  box.  Even  with  a  candle  underneath  the  box 
the  figures  were  visible,  but  of  course  not  so  sharp  as  when  the  oxy-hydrogen 
light  was  used.  This  experiment  led  me  to  devise  the  following  arrangement, 
which,  with  such  liquids  as  I  have  tried,  serves  admirably,  the  figures  being 
projected  on  to  the  screen  with  great  clearness: 

“  In  the  first  place,  several  troughs  are  made  to  hold  the  water  on  which  to 
place  the  creosote,  &c.  Those  I  have  are  made  of  plate  glass.  A  piece  of 
glass  5  in.  square  and  J  in.  thick,  has  a  hole  3  in.  diameter  cut  in  it,  and  this, 
when  laid  on  a  plain  piece  of  glass,  forms  a  circular  trough,  3  in.  diameter  and 
i  in.  deep.  An  ordinary  oxy-hydrogen  lantern,  from  which  the  nozzle  has  been 
removed,  is  now  tilted  back  so  that  the  light  from  the  lantern  is  thrown  perpen- 


ADHESION. 


583 


dicularly  upward,  and  the  trough  placed  just  over  the  front  of  the  lantern  as 
though  it  were  a  lantern-slide.  1'he  nozzle  of  the  lantern,  fitted  to  a  projecting 
arm,  is  then  brought  over  the  trough,  and  an  image  of  the  upper  surface  of 
the  water  obtained  on  the  ceiling.  On  now  placing  a  drop  of  creosote  on  the 
water,  an  image  of  it  is  seen  on  the  ceiling.  If  it  be  desired  to  throw  the 
image  on  to  a  vertical  screen,  a  reflecting  prism  is  p’.aced  on  the  nozzle,  by  which 
the  desired  effect  is  obtained. 

*■  The  arrangement  will  be  completely  understood  by  referring  to  the  accom¬ 
panying  figure,  in  which  A  is  the  lantern  turned  back  ;  c,  the  chimney  ;  B,  the 

glass  trough  to  hold  the  water 
on  which  the  creosote  or  other 
liquid  is  placed ;  D,  nozzle  of 
lantern,  supported  by  the  hori¬ 
zontal  arm  E;  F,  the  reflecting 
prism ;  s,  screen  on  which  the 
image  is  received. 

“  It  should  be  mentioned  that 
it  is  necessary  to  remove  the 
usual  taper  pipe  of  the  nozzle 
of  the  lantern,  and  substitute 
a  shorter  one,  so  that  the  figures 
may  be  properly  focussed,  and 
yet  room  enough  left  to  intro¬ 
duce  a  pipette  between  the 
nozzle  and  the  trough  contain¬ 
ing  the  water.” 

Adhesion  (ad  to,  and  hareo 
to  stick),  the  tendency  which 
dissimilar  bodies  have  to  ad¬ 
here  or  stick  together,  is  ex¬ 
pressed  by  Daniell  in  Johnson¬ 
ian  grandeur  as  “heterogeneous 
adhesion.”  Water  dropped  into 
a  polished  silver  spoon  wets  it: 

Jhe  fluid  adheres  to  the  solid. 

Absolutely  clean  platinum  may  be  quicksilverized  (is  it  right  to  say  wetted  ?) 
with  mercury:  the  fluid  metal  adheres  to  the  solid  metal;  and  this  property 
is  taken  advantage  of  in  the  perfection  of  barometers,  in  order  to  prevent  the 
air  adhering  to  the  interior  of  the  barometer,  creeping  up  the  sides  of  the  tube, 
and  displacing  the  mercury. 

Negretti  and  Zambra  skilfully  prevent  the  deterioration  of  their  instruments 
by  a  method  of  this  kind. 

Portland  cement,  ordinary  mortar,  compositions  used  for  sticking  the  parts 
of  broken  china  together,  all  act  in  a  similar  manner— by  adhesion. 

There  are  certain  curious  modifications  of  adhesion,  which  have  engaged 
the  most  careful  attention  of  learned  scientific  men.  The  particular  cases  that 
will  be  mentioned  here  are  those  of  “  Osmose”  and  “  Dialysis.” 

The  word  “osmose”  is  derived  from  the  Greek  0/07x15,  impulsion. 

Dialysis  (81a  asunder,  A1V15  separation)  means  the  separation  of  certain 
substances  through  the  intervention  of  somebody,  such  as  parchment  paper, 
through  which  liquid  diffusion  may  take  place. 


Tic:.  463. 


584 


CHE  MIS  TR  Y. 


Many  years  ago,  Dutrochet  studied  the  passage  of  liquids  through  porous 
bodies,  and  his  original  instrument,  called  the  endosmometer,  has  been  con¬ 
structed  over  and  over  again  by  students  at  medical  schools,  who  wished  to 
verify  for  themselves  the  remarkable  fact,  so  suggestive  of  the  explanation  of 
some  of  the  elaborate  processes  which  go  on  in  the  economy  of  the  human  body. 

Dutrochet’s  instrument  consisted  virtually  of  a  glass  funnel  with  a  long  and 
narrow  tube.  The  mouth  of  the  funnel  should  be  ground  flat,  and  a  piece  of 
bladder  strained  nicely  and  fixed  securely  over  it.  Into  the  funnel  may  be 
poured  some  alcohol  and  water,  coloured  blue  with  a  little  indigo;  and  when 
this  is  placed  in  a  shallow  vessel  or  plate  containing  water,  the  latter  passes 
through  the  bladder  and  gradually  diffuses  into  the  alcohol,  so  that  the  liquid 
in  the  funnel  rises,  contrary  to  the  law  of  gravitation,  and  might  overflow  if 
the  tube  of  the  funnel  were  not  long  enough.  This  effect  is  due  to  the  fact  that 
the  bladder  is  more  easily  wetted  by  water  than  by  alcohol :  the  water  adheres 
to  the  bladder  in  a  greater  degree  than  alcohol,  and  therefore  its  lower  sur¬ 
face  dipping  into  the  water  in  the  plate,  is  first  moistened  with  water.  When 
the  latter  has  risen  by  capillary  attraction  and  filled  the  pores  of  the  mem¬ 
brane,  it  has  reached  the  upper  surface  where  the  alcohol  exists ;  and  here,  by 
the  adhesion  taking  place  between  the  twm  fluids,  the  plain  water  and  the 
spirit,  they  diffuse  themselves  through  each  other,  and  so  the  process  continues; 
which  increases  the  bulk  of  the  fluid  in  the  funnel ;  and  as  the  flow  is  from 
the  outside  to  the  inside,  it  is  called  endosmosis  (ivBov  inwards,  and  a/oytos 
impulse);  at  the  same  time  a  reversal  of  the  process  is  going  on,  by  w'hich  a 
small  quantity  of  the  alcohol  passes  from  the  inside  to  the  outside,  and  this, 
being  exactly  contrary  to  the  other,  is  called  exosmosis ,  outward  impulse. 

Whichever  liquid  wets  the  membrane  most  freely  determines  the  direction 
of  the  impulse.  Thus,  if  another  funnel  be  covered  with  a  membrane  com¬ 
posed  of  a  thin  film  of  collodion,  as  the  alcohol  wets  the  latter  quicker  than 
w'ater,  the  flow  would  be  more  rapid  from  the  inside  to  the  outside,  and  the 
former  experiment  with  the  bladder  would  be  reversed,  the  liquid  in  the  funnel 
falling  instead  of  rising. 

Professor  Graham  has  taken  up  the  subject  and  examined  the  phenomena 
in  the  most  patient  and  laborious  manner,  and  his  experiments  show  that 
osmose  depends  essentially  on  the  chemical  action  of  the  liquid,  on  the  parti¬ 
cular  porous  matter  or  septa  used  :  the  corrosion  of  the  septum  seems  to  be  a 
necessary  condition  of  the  flow,  nia  experiments  were  made  with  saline 
substances  ;  and,  as  a  proof  of  the  correctness  of  the  explanation,  it  wras  found 
that  tanned  sole-leather,  though  a  porous  substance,  showed  no  osmose  or 
impulse  either  way,  because  it  is  not  acted  upon  by  saline  solutions. 

To  set  up  osmose  the  chemical  action  should  be  different  on  the  two  sides  of 
the  membrane,  and  therefore  an  alkaline  solution  on  one  side  and  an  acid 
one  on  the  other  gave  some  of  the  best  results,  the  flow  of  water  being  chiefly 
towards  the  alkaline  or  basic  side.  The  solution  should  not  be  too  strong,  or 
the  pores  may  become  stopped  by  the  particles  of  the  salt. 

Graham  calls  the  rising  of  the  fluid  in  the  osmometer  positive  osmose j  the 
reverse,  negative  osmose.  His  elaborate  researches  are  to  be  found  in  the 
“  Philosophical  Transactions,”  1854,  p.  177,  and  “  Chemical  Society’s  Journal,” 
Vol.  VIII.,  p.  43. 

Osmose  no  doubt  plays  a  most  important  function  in  the  economy  of  life, 
and  promotes  that  combination  of  acids  and  alkalies  already  alluded  to  as  the 
probable  source  ol  the  currents  of  electricity  in  the  human  body. 


ADHESION. 


585 


Dialysis.— This  department  of  physical  attraction  Professor  Graham  has 
made  peculiarly  his  own,  and,  by  working  out  the  principle  of  liquid  diffusion, 
has  added  another  mode  of  analysis  to  those  previously  known. 

He  divides  all  soluble  substances  into  two  classes,  which  he  terms  crystal¬ 
loids  and  colloids. 

Bodies  capable  of  crystallization,  such  as  sugar  or  common  salt,  would 
belong  to  the  first,  and  they  are  found  to  have  a  greater  power  of  diffusive 
mobility  through  porous  septa. 

Substances  incapable  of  crystallization,  called  colloids  from  ko'AAtj,  glue, 
such  as  many  animal  substances — albumen,  gelatine,  or  glue;  or  other  bodies — 
gum,  caramel,  or  starch,  do  not  diffuse  themselves  easily  through  septa,  and  do 
not  assume  a  crystalline  form ;  they  are,  moreover,  nearly  tasteless. 

The  experiment  can  be  made  by  stretching  an  insoluble  colloid,  such  as 
parchment  paper,  over  a  hoop  made  of  gutta-percha,  thus  forming  a  shallow 
tray.  If  this  be  floated  in  a  porcelain  dish  containing  distilled  water,  taking 
care  that  the  bulk  of  the  latter  is  nine  or  ten  times  that  of  the  contents  of  the 
tray,  a  direct  separation  of  a  body,  such  as  arsenious  acid,  may  take  place ; 
and  supposing  a  complex  mixture  of  soup,  milk,  sugar,  tea,  beer,  and  arsenious 
acid  is  put  into  the  tray,  in  the  course  of  twenty-four  or  forty-eight  hours  arsenic 
may  be  detected  in  the  water  in  the  porcelain  dish  so  nearly  free  from  organic 
matter  that  the  water  may  be  evaporated  to  a  small  bulk,  and  the  test  of  sul¬ 
phuretted  hydrogen  applied  at  once,  when  the  usual  characteristic  yellow  ter- 
sulphidc  may  be  obtained  on  the  addition  of  a  little  hydrochloric  acid. 

There  are  many  other  important  separations  which  may  be  conducted  in  a 
similar  manner,  and  the  whole  subject  is  fully  discussed  in  Graham’s  paper, 
“Philosophical  Transactions,”  1861,  p.  183. 


586 


CHEMISTRY. 


CHEMICAL  ACTION. 

This  power  may  refer  to  many  changes :  the  combination  of  oxygen  with 
iron  taking  place  slowly  in  the  cold  dead  iron  railings  fencing-in  our  dwelling- 
houses  ;  the  slow,  the  indirect,  but  sure  attacks  of  the  same  element  on  the 
dwelling-house  of  the  soul,  the  human  constitution,  bring  about  the  inevitable 
wearing  away  of  the  vital  battery — the  energy  that  will  not  for  ever  respond 
to  the  will  of  the  possessor ;  ana  tnus  oid  age  is  equivalent  to  rust,  and  the 
ordinary  functions  of  the  body  that  support  life  come  to  an  end  by  what  is 
spoken  of  in  connection  with  dead  matter  as  “  reasonable  wear  and  tear.” 
The  first  entry  of  air  to  the  lungs  of  the  new-born  infant  is  proclaimed  with  a 
cry  that  may  be  repeated  in  another  tone  as  the  last  gasp  of  air  passes  spas¬ 
modically  from  the  lips  of  the  departing  aged. 

Carbon,  oxygen,  hydrogen,  .  nitrogen,  sulphur,  phosphorus,  and  certain 
earthy  and  saline  matters  individually  have  characteristic  properties,  and  all 
of  these,  with  the  mystery  of  vital  force,  contribute  to  build  up  the  human 
body.  How  natural,  then,  to  define  “chemical  action”  to  be  that  change 
which  takes  place  when  one  or  more  substances  unite  and  form  another  or 
other  bodies  perfectly  different  from  those  that  were  engaged  in  forming  it  or 
them 

It  is  chemical  action  that  maintains  the  greatest  of  all  results — vitality — 
whether  observed  in  the  animal  or  vegetable  kingdom. 

Mercury  is  a  brilliant  opaque  fluid  metal :  it  is  sometimes  called  quick  silver, 
because  it  is  difficult  to  catch.  Chlorine  is  a  green  gas,  very  potent  and 
aggressive,  and  these  qualities  render  it  hurtful  to  the  lungs,  and,  if  inhaled,  it 
may  excite  a  cough  of  a  violent  description.  All  these  physical  properties 
change  when  the  two  unite  to  form  a  white,  inodorous,  insipid  substance,  in¬ 
soluble  in  water — a  useful  medicine,  and  commonly  called  calomel;  and  their 
properties  change  again  if  more  chlorine  is  united  to  the  mercury,  when  the 
resulting  salt  is  found  to  be  soluble  in  water,  and  possesses  an  acrid,  nauseous 
taste  that  lingers  long  in  the  mouth,  and  is  a  most  violent  poison.  It  is  no 
longer  called  calomel,  but  corrosive  sublimate;  i.e.,  these  are  only  the  vulgar 
names:  strictly  speaking,  science  calls  tne  former  mercurious  chloride,  HgaCli, 
and  the  latter  mercuric  chloride,  HgCt2. 

Chemical  action  or  attraction  is,  therefore,  a  subtle  power  possessing  won- 
drously  energetic  qualities  capable  of  operating  on  the  minutest  particles  of 
matter,  at  distances  that  the  most  refined  means  cannot  measure. 

There  are  laws  that  rule  chemical  attraction,  as  with  the  other  forces,  such 
as  electricity,  magnetism,  &c. 

I.  Definite  Proportions ,  viz.,  all  elements  uniting  with  other  elements, 
combine  in  certain  fixed  and  invariable  proportions,  as  shown  in  the  table, 
page  542.  The  composition  of  pure  water  cannot  vary:  it  may  be  the  product 
of  a  thousand  different  changes,  but  its  constituents  are  fixed  to  certain  pro¬ 
portions, — the  weight  of  the  oxygen  is  always  eight  times  that  of  the  hydrogen. 

II.  Multiple  Proportions. — When  one  body  enters  into  combination  with 
another  in  different  proportions,  the  numbers  indicating  the  greater  propor¬ 
tion  are  simple  multiples  of  that  denoting  the  smaller  proportion. 


CHEMICAL  ACTION. 


587 


7. 

2. 

3- 

4 

c 


77 

77 

77 

77 


32 

48 

64 

80 


Nitrous  oxide  contains  28  parts  nitrogen  to  16  of  oxygen 
Nitric  oxide  ,,28 

Nitric  trioxide  „  28 

Nitric  tetroxide  „  28 

Nitric  pentoxide  „  28 

\\  e  may  paraphrase  the  above,  and  put  it  thus : 

A+B,  A  +  2B,  A  +  3B,  A+4B,  A-1-5B. 

III.  Equivalent  Proportions  result  from  Law  I.,  and  every  element  dis¬ 
placing  another  does  so  in  fixed  numerical  proportions.  Knowing  the  com¬ 
bining  weight  of  mercury,  and  supposing  it  to  be  united  with  an  atom  of  iodine 
it  is  easy  to  see,  by  looking  at  the  table  of  atomic  weights  (page  542),  what 
proportion  of  chlorine  would  be  required  to  replace  one  atom  of  iodine  or 
how  much  calcium  would  be  required  to  replace  magnesium  if  the  former  were 
separated  from  its  atomic  or  combining  proportion  of  sulphuric  acid 

I  .  Gaseous  or  aeriform  bodies  combine  in  proportions  which  can  be  ascer- 
tained  by  exact  volumes  having  a  very  simple  relation  to  each  other 

I  he  ratios  may  be  1  volume  of  A  to  1  of  B,  i.e.,  the  gases  may  unite  in 

Ato  3  o°f  IT5 ;  or  1  of  A  t0  2  of  B  J  or  1  of  A  to  3  of  B ;  or  sometimes  2  of 

usually1  observed.31100  ^  ***  tW°  g3SeS  by  Volume’  this  siniPle  Proportion  is 

An  atomic  weight  of  any  particular  substance,  when  converted  into  the 
vofumeS  StatC  at  thC  SamC  temperature  and  pressure,  always  yields  the  same 

1  gramme  of  hydrogen  at  320  F.  and  29-92  in.  barometer,  i.e.,  ) 

o°  C.  and  760  millimetres  (  ~~11  ‘9 

16  „  oxygen  „  „  „  =1119 

3>5  „  chlorine  „  „  „  =iri9 

' $5  abo,v<r  U,wl11  be  seen  that  equal  volumes  give  a  variety  of  weights, 
11  19  litres  of  hydrogen  weighing  only  1  gramme,  and  11-19  litres  of  chlorine 
weighing  35  5  grammes.  If  this  arrangement  of  volumes  and  weights  is  re¬ 
versed  and  equal  weights  are  taken  of  the  above-named  elements,  it  is  evident 
that  the  volumes  will  differ.  So  that  the  difference  between  combinations 
by  weight  and  volume  must  always  be  remembered  in  chemical  combinations. 

2  gases  in  equal  volumes,  represented  by  two  squares,  may  unite  ) 

and  form  .  .  .  .  .  .  ’  | 

3  volumes  may  be  condensed  into 


n 


. . !  T~ 1 

3  ”  »»  77  1  Q 

”  »  77  . 1  LH 

1  he  like  reasoning  applies  to  compound  gases  and  vapours,  which  unite  in 
uj  same  simple  ratio  of  volumes  with  reference  to  their  atomic  weights, 
j  *  do,es  not.seem  to  be  possible  to  create  a  large  volume,  or  increase  the 
1’ilk,  of  any  given  volumes  of  gases  that  combine  with  each  other.  There  is 
thus  a  constant  relation  between  the  atomic  weights  and  volumes  of  bodies  in 
tne  gaseous  or  vaporous  state. 


588 


CHEMISTR  K 


NOMENCLATURE. 

Before  chemistry  existed  as  a  science,  substances  received  their  names  from 
their  real  or  supposed  properties,  or  from  some  circumstance  connected  with 
their  production.  Thus  phosphorus  is  derived  from  two  Greek  words  s  and 
< fczpeiv  (to  bear  light).  The  name  ammonia  is  said  to  be  derived  from  its 
being  produced  in  quantity  by  the  decomposition  of  animal  matter  around  the 
temple  of  Jupiter  Ammon.  Potash  also  received  its  name  from  the  ancient 
means  of  procuring  it.  This  was  effected  by  burning  wood  in  open  iron 
“  pots :  ”  the  ashes  were  hence  called  “  pot-ashes.” 

Some  substances  were  named  after  the  stars  and  planets,  as  lunar  caustic, 
t.e.,  nitrate  of  silver ;  mercury,  quicksilver.  Thus  we  see  the  names  of  most 
substances  were  given  in  an  unsystematic  manner. 

To  the  elements  recently  discovered  some  attempt  has  been  made  to  give 
names  with  like  terminations  to  those  elements  which  resemble  one  another. 
Thus  three  elements  e  iding  in  on,  and  resembling  each  other  in  properties  in 
some  respects,  are  caroon,  boron,  and  silicon. 

Chlorine,  bromine,  iodine,  and  fluorine  form  another  group  resembling  one 
another,  and  all  terminating  in  ine. 

The  termination  um  is  indicative  of  a  metal,  as  sodium  and  potassium ;  and 
if  the  Latin  names  be  used,  all  the  metals  will  be  found  to  end  in  um ,  as 
ferrum  (iron),  plumbum  (lead),  argentum  (silver),  &c.  With  the  exception  of 
selenium,  no  non-metal  terminates  in  um. 

It  is  the  object  of  chemical  nomenclature  not  only  to  name  substances,  but 
also  through  their  names  to  give  the  knowledge  of  the  elements  of  which  they 
are  composed,  and,  as  far  as  possible,  their  propoition. 

Speaking  of  classification  and  nomenclature,  Dr.  Hofmann,  in  the  preface 
to  his  “  Modern  Chemistry,”  says:  “The  domain  of  chemical  philosophy  has, 
for  many  years  past,  rather  resembled  a  tumultuous  battle- plain  than  a  field 
bestowed  by  Nature  for  peaceful  cultivation  by  mankind.”  And  a  learned 
critic  in  the  “Athenaeum,”  alluding  to  that  passage,  remarks:  “  But  there  are 
many  thoughtful  observers  who,  looking  upon  that  cultivated  domain,  are  dis¬ 
posed  to  believe  that  the  flowers  are  likely  to  be  choked  by  weeds,  in  the  shape 
of  an  endless  number  of  hypothetical  radicals,  most  complex  formulae,  and  an 
unpronounceable  nomenclature.  On  the  first  introduction  of  the  new  chemical 
philosophy,  Herschel  explained  his  objections  to  the  alteration  of  the  term 
muriatic  acid  into  hydrochloric  acid.  The  evils  which  he  then  foresaw  have 
been  more  than  realized,  and  the  literature  of  chemistry  is  now  deformed  with 
such  names  as  platino-cyanide  of  diplatosammonium,  cymyl-dithionite  of 
sodium,  bromide  of  triammo-dicu-pro-diammonium,  and  formulae  extending 
across  an  octavo  page;  so  that  a  treatise  of  chemistry  has  very  much  the 
appearance  of  a  book  written  in  an  unknown  language.  ‘  It  is  not  necessary 
to  the  progress  of  this  science,’  write  two  eminent  modern  chemists,  ‘that  its 
language  should  change  with  the  opinions  of  every  new  theorist.  .  .  They 

have  apparently  been  engaged  in  working  out  an  idea,  and  seeking  for  some 


NOMENCLA  TURE . 


589 


Utopian  standard  of  perfection  in  a  new  system  of  notation ;  but  in  endea¬ 
vouring  to  settle  contested  points  on  a  firmer  basis,  they  have  incurred  the 
risk  of  unsettling  everything.’” 

When  two  elements  unite  together  they  form  what  is  called  a  binary  com¬ 
pound,  such  as  oxide  of  zinc,  or  zincic  oxide.  This  name  gives  at  once  the 
knowledge  that  the  compound  consists  of  two  elements,  zinc  and  oxygen,  one 
equivalent  of  each  being  in  the  compound. 

The  non-metallic  elements  combined  with  each  other,  or  with  the  metals, 
form  the  principal  binary  compounds. 

In  the  following  table*  is  shown  the  nomenclature  of  binary  compounds: 
the  symbols  of  the  compounds  are  in  the  fifth  column. 


The  Compounds  of 

Are  termed 

Oxygen . ."t... 

Oxides  . 

Chlorine  . 

Chlorides  ... 

Bromine  . 

Bromides  ... 

Iodine  . 

Iodides  . 

Fluorine  . 

Fluorides  ... 

Nitrogen  . 

Nitrides  . 

Carbon . 

(  Carbides  or 
)  Carburets 

Sulphur . 

(  Sulphides  or 
\  Sulphurets 

Selenium  . 

1  Selenides  or 
l  Seleniurets 

Phosphorus  . 

<  Phosphidesor 
\  Phosphurets 

For  example  . 


Or  in 
Symbols, 


or 

Zincic  oxide 
(  Argentic 
^  chloride 
(  Sodic  brom¬ 
ic  ide 

C  Potassic  iod- 
(  ide 

(  Potassic  flu- 
[  oride 


Boric  nitride 


Nitric  carbide 
(cyanogen) 

S  Cupric  sulph¬ 
ide 

Plumbic  do. 

r  Mercuric  7 
)  selenide  j 

V  Cadmic  do. 

(  Calcic  phas¬ 
ic  phide 


Oxide  of  zinc 
Chloride  of 
silver 

Bromide  of  so¬ 
dium 

Iodide  of  po¬ 
tassium 
Fluoride  of  po¬ 
tassium 
C  Nitride  of  bo- 
(  ron 

Carbide  of  ni¬ 
trogen 

(  Sulphide  of 
l  copper 
(  Sulphuret  of 
l  lead 
Selenide  of 
mercury 
f  Seleniuret  of 
l  cadmium 
Phosphuret  of 
calcium 


} 

) 

) 

) 

l 

7 

i 

! 

I 

1 

} 

7 


I 


ZnO 

AgCl 

NaBr 

KI 

KF 

BN 

CN 

CuS 

PbS 

HgSe 

CdSe 

CaP 


In  employing  symbols,  the  symbol  of  the  basylous  or  electro-positive  element 
is  generally  placed  first. 

When  the  same  elements  unite  in  various  proportions,  Latin  or  Greek  nu¬ 
merals  are  used  as  prefixes  to  distinguish  between  the  different  compounds  of 
the  same  elements.  Thus  the  first  oxide  of  ruthmium  is  called  the  protoxide, 
RuO  ;  the  second  oxide  is  called  the  deutoxidc,  RuOa;  the  third  is  named  the 
trioxide,  Ru03. 

The  name  binoxide  is  applied  to  the  oxide  that  contains  twice  as  much 
oxygen  as  the  protoxide.  _ 


*  From  Miller's  "  Elements  of  Chemistry,”  Part  II. 


CHEMISTR  Y 


59 o 


M'he  prefix  sesqui  is  given  to  compounds  which  contain  two  elements  in  the 
proportion  of  3  to  2,  or  i  -|  to  1,  as  sesquioxide  of  ruthmium,  Ru203.  The  pre¬ 
fix  per  signifies  the  highest  combinations,  as  perchloride  of  mercury. 

Many  oxides  form,  when  united  with  the  elements  of  water,  acids. 

Some  bodies  have  two  or  more  oxides,  which  form,  with  the  elements  of 
water,  acids;  and  in  order  to  distinguish  between  them  a  certain  nomencla¬ 
ture  is  made  use  of.  Thus  the  name  of  the  acid  containing  the  largest  pro¬ 
portion  of  oxygen  terminates  in  ic ,  as  sulphuric  acid,  H2S04,  and  that  with 
the  less  amount  ends  in  ous,  as  sulphurous  acid,  H2S03. 

An  acid  has  sometimes  been  discovered  containing  a  larger  proportion  of 
oxygen  than  the  one  to  which  the  termination  ic  had  been  given.  Then  the 
prefix  per  has  been  used  to  denote  this,  as  chloric  acid  HC103,  and  perchloric 
acid,  HC104. 

An  acid  containing  less  oxygen  than  the  one  ending  in  ous  has  the  prefix 
hypo ,  as  chlorous  acid,  HC102,  hypochlorous  acid,  HCIO. 

Besides  these  acids  which  contain  oxygen,  there  are  others  which  contain 
no  oxygen  ;  for  instance,  hydrogen  and  chlorine  combine  to  form  hydrochloric 
acid,  HC1;  also  hydrogen  and  iodine  form  hydriodic  acid,  HI. 

In  the  naming  of  the  oxysalts — the  union  of  an  oxyacid  with  a  base — the 
name  of  the  salt  containing  the  acid  with  the  largest  proportion  of  oxygen 
terminates  in  ate ,  as  the  compound  of  sulphuric  acid  and  soda  is  called  disodic 
sulphate,  or  sulphate  of  sodium,  Na2S04;  whilst  the  salt  of  the  acid  containing 
less  oxygen,  and  terminating  in  ous ,  ends  in  ite ,  as  the  compound  of  sulphurous 
acid  and  soda  is  named  disodic  sulphite,  or  sulphite  of  sodium,  Na2S03. 

When  a  metal  forms  more  than  one  basic  oxide,  i.e.,  more  than  one  oxide 
capable  of  forming  salts  by  the  action  of  acids,  the  name  of  the  metal  in  the 
oxide  containing  the  smaller  proportion  of  oxygen  ends  in  ous;  and  in  the 
oxide  containing  the  larger  amount  of  oxygen  it  terminates  in  ic ,  as  in  the 
case  of  iron. 

The  protoxide  is  called  ferrous  oxide,  FeO,  and  the  salts  of  this  oxide  ferrous 
salts,  as  ferrous  sulphate,  FeS04  (  +  7  H20,  water  of  crystallization). 

The  sesqui  oxide  is  termed  ferric  oxide,  Fe2Os,  and  its  salts  ferric  salts,  as 
ferric  sulphate,  Fe23S04. 

Most  chemists  of  note  now  look  upon  acids  as  salts  of  hydrogen,  the  latter 
representing  the  metallic  part.  And  when  these  hydrogen  salts  act  upon  other 
metals,  they  look  upon  the  reaction  as  a  replacement  of  hydrogen.  There  is  no 
doubt  that  this  system  is  quite  consistent,  and  much  more  in  accordance  with 
observed  facts,  than  the  older  ideas,  wnich  are  daily  losing  ground. 

When  a  molecule  of  an  acid  contains  one  atom  of  hydrogen  capable  of  being 
replaced  by  one  atom  of  a  monad  metal,  it  is  called  a  monobasic  acid,  such 
as  nitric  acid,  H  N  03,  the  hydrogen  of  which  can  be  replaced  by  one  atom  of  the 
monad  metal  potassium.  If  it  contain  two  atoms  of  replaceable  hydrogen, 
it  is  called  dibasic,  such  as  sulphuric  acid,  H2S04,  the  two  atoms  of  hydrogen 
which  it  contains  being  replaceable  by  two  atoms  of  a  monad  metal  like  potas¬ 
sium,  or  one  atom  of  a  dyad  metal  such  as  copper.  Those  bodies  which  con¬ 
tain  more  than  one  atom  of  replaceable  hydrogen  are  called  polybasic. 

The  terms  monad,  dyad,  triad,  tetrad,  pentad,  and  hexad  are  used  to  denote 
the  equivalents  of  the  different  elementary  bodies  in  compounds  as  compared 
with  hydrogen. 

If  we  compare  the  equivalents  of  the  elements  in  compounds  with  hydrogen, 
we  find  that  they  differ  very  much  in  value.  Thus-. 


NO  MENC LA  TU RE.  5  9 1 


The  monad  potassium  is 

equivalent  to 

1  atom  of  hydrogen 

in  a  compound. 

The  dyad  zinc 

2  atoms  of 

55 

The  triad  bismuth 

V 

3 

?? 

The  tetrad  platinum 

4 

5) 

55 

The  pentad  nitrogen  * 

>5 

5 

55 

55 

The  hexad  manganese 

6 

55 

55 

TABLE  OF  THE  SYMBOLS,  AND  NEW  AND  OLD  COMBINING  OR 
ATOMIC  WEIGHTS  OF  THE  ELEMENTS. 


Names  of 
Elements. 

Symbol 

New 
At.  Wt 

Old 
At.  Wt. 

Names  of 
Elements. 

Symbol. 

New 
At.  Wt. 

Old 
At.  Wt 

Aluminium  ... 

A1 

27*4 

1  37 

Molybdenum. . 

Mo 

96  O 

48-0 

Antimony . 

Sb 

I  22'0 

— 

Nickel 

Ni 

59’° 

293 

Arsenic . 

As 

75‘° 

1 37 '° 

— 

Niobium  . 

Nb 

94-5 

I4-0 

_ 

Barium . 

Ba 

68-5 

Nitrogen  . 

N 

— 

Bismuth  . 

Bi 

2  IO'O 

_ 

N  orium . 

No 

_ 

_ 

Boron  . 

B 

109 
80 -o 

_ 

Osmium  . 

Os 

*99'° 

i6-o 

99'4 

8-o 

Bromine  . 

Br 

— 

Oxygen . 

O 

Cadmium . 

Cd 

I  I  2'0 

56-0 

Palladium . 

Pd 

106-5 

53*25 

Caesium  . 

Cs 

133'° 

— 

Phosphorus  ... 

P 

31-0 

Calcium  . 

Ca 

400 

20'0 

Platinum  . 

Pt 

197-2 

98-56 

Carbon . 

C 

I  2‘0 

6"0 

Potassium  ... 

K 

39’ 1 

Cerium . 

Ce 

Q2'0 

460 

Rhodium  . 

Rh 

104-2 

853 

52-1 

Chlorine  . 

Cl 

35*5 

Rubidium . 

Rb 

Chromium  ... 

Cr 

52-5 

26-25 

Ruthmium  ... 

Ru 

104-2 

52-1 

Cobalt  . 

Co 

59'° 

29-5 

Selenium  . 

Se 

793 

3975 

Copper  . 

Cu 

63A 

317 

Silicon  . 

Si 

28-0 

14-0 

Didymium  ... 

D 

96-0 

480 

Silver  . 

Ag 

io8‘o 

— 

F.rhinm 

E 

1 14‘6 
19-0 

_ 

Sodium . 

Na 

23-0 

873 

_ 

Fluorine  . 

F 

— 

Strontium . 

Sr 

43'8 

Glucinutn . 

Gl 

9'4 

47 

Sulphur . 

Tantalum . 

S 

32-0 

1 6-o 

Gold 

Au 

196-6 

ro 

_ 

Ta 

1376 

129-0 

68-8 

Hydrogen  ... 

H 

— 

Tellurium . 

Te 

64-5 

I  ndium 

In 

74-0 

I27‘0 

197-2 

56-0 

92'0 

_ 

Thallium  . 

T1 

204 'O 
1157 

1  i8-o 

_ 

Iodine  . 

I 

Thorium  . 

Th 

593 

59-0 

25-0 
92  0 

I  ridium 

Ir 

98-6 

28-0 

Tin  . 

Sn 

1  ron 

Fe 

Titanium  . 

Ti 

500 

184-0 

Lanthamium. . 

La 

Tungsten  . 

W 

Lead 

Pb 

207-0 

7'° 

1033 

Uranium  . 

U 

120*0 

6o'o 

Lithium  . 

Li 

Vanadium  ... 

V 

137-0 

68-5 

Magnesium  ...j  Mg 

24*3 

12-15 

Yttrium . 

Y 

617 

— 

Manganese 

Mn 

55-0 

27-5 

Zinc  . 

Zn 

65-0 

32-5 

Mercury 

Hg 

200'0 

1000 

Zirconium . 

Zr 

893 

4475 

The  above  is  a  list  of  the  elemert  at  present  known  to  chemists,  with 


*  Usually  triad,  sometimes  pentad. 


CHEMISTRY. 


592 


their  symbols,  and  their  new  and  old  combining  or  atomic  weights.  As  it  would 
be  inconvenient,  in  expressing  chemical  reactions  in  writing,  to  write  the 
•whole  name  of  an  element,  the  first  or  first  two  letters  of  the  name  are  used 
as  symbols  to  denote  any  particular  element;  thus  O  stands  for  oxygen,  H  for 
hydrogen,  Co  for  cobalt.  In  the  case  of  some  metals,  the  first  and  prominent 
letters  of  the  Latin  name  are  used  as  symbols,  as  Ag  for  silver  (argentum), 
Pb  fcr  lead  (plumbum).  The  first  two  letters  of  the  name  of  an  element  are 
used  as  its  symbols  when  there  is  another  element  beginning  with  the  same 
letter.  Thus  C  is  used  as  the  symbol  of  carbon,  and  Cl  is  used  tor  chlorine, 
in  order  to  distinguish  between  the  two.  The  symbol  of  an  element  when 
used  by  itself  not  only  stands  for  that  element,  but  also  for  a  certain  propor¬ 
tion  thereof  by  weight,  called  its  atomic  weight ;  such  proportion  being  the 
smallest  proport  on  by  weight  in  which  such  element  combines  with,  or  is 
eliminated  from,  a  chemical  compound,  hydrogen  being  taken  as  unity. 

Thus  C  does  not  stand  merely  for  carbon,  but  also  for  exactly  12  parts  by 
weight  of  carbon,  or  O  stands  (or  16  parts  of  oxygen. 

The  small  figure  placed  to  the  right  hand  of  the  symbol  of  an  element  sig¬ 
nifies  the  number  of  atoms  of  that  element.  Thus  C.  means  4  atoms,  or  4X  12 
parts  of  carbon  ;  02  means  2  atoms,  or  2  X  16  parts  of  oxygen. 

The  symbols  of  compounds  are  made  by  placing  the  symbols  of  the  elements 
forming  the  compounds  side  by  side,  as 

Water  . . H20 

Sulphuric  acid  .....  H2S04 

Ammonia  ......  H3N 

When  more  than  one  molecule  of  a  compound  has  to  be  denoted,  a  ’arge 
figure  is  placed  to  the  left  hand  of  the  formula  of  the  compound,  and  all  the 
symbols  in  the  formula  are  multiplied  by  the  large  figure  which  stands  before 
it;  thus  2H20  means  two  molecules  cf  water.  * 

Chemical  reactions  are  expressed  by  equations.  The  symbols  of  the  ele¬ 
ments  before  the  change  are  placed  on  one  side  of  the  equation,  and  the 
symbols  representing  the  change  effected  on  the  other,  thus : 

KN03+H2S04  =  HN03+  HKS04 

Nitre  anti  sulphuric  ■  Nitric  ,  hytlric  potas- 
acid  ^lve  acid  aiia  slum  sulphate. 

It  is  necessary  to  distinguish  clearly  between  the  terms  atom  and  molecule. 
An  atom  means  something  which  cannot  be  further  subdivided.  And  thus, 
in  the  table  of  elements  (p.  542)  O  stands  for  one  atom  of  oxygen,  H  fcr  one 
atom  of  hydrogen.  A  molecule  may  contain  more  than  one  atom,  as,  for  in¬ 
stance,  H2:  this  would  be  called  a  molecule  containing  two  atoms  of  hydro¬ 
gen  ;  H20  would  be  a  molecule  of  water;  and  H202  a  molecule  of  peroxide  of 
hydrogen  or  hydric  peroxide,  or  oxygenated  water.  These  expressions  are 
most  important,  and  prevent  the  confusion  of  the  term  “  atomic  ”  with  that  of 
“equivalent,”  because  they  are  quite  different  from  each  other.  A  molecule 
is  very  properly  defined  by  Roscoe  to  be  “the  group  of  atoms  forming  the 
smallest  portion  of  a  chemical  substance,  either  simple  or  compound,  which 
can  exist  in  the  free  state.”  And  he  gives  a  good  illustration  of  the  difference 
between  atomic  and  molecular  formulae  in  the  following :  H  4-0=  HC1  is  the 
atomic  expression,  whilst  H2-fCl2  —  2HCI  is  the  molecular  expression  for  the 
same  reaction. 


OXYGEN. 


593 


ELEMENTS  WHICH  ARE  NOT  METALLIC. 

OXYGEN. 

Symbol,  O.  Atomic  weight,  16. 

In  the  month  of  August,  1774,  Dr.  Priestly  discovered  this  important 
element,  and  Mr.  George  Rod  well  has  very  properly  insisted,  in  a  learned 
paper  in  the  “  Chemical  News,”  that  it  was  not  discovered  by  Swedenborg 
half  a  century  before  Priestley,  and  that  there  is  not  a  particle  of  reliable  evi¬ 
dence  in  support  of  this  statement.  “  We  are  quite  unable,”  says  Mr.  Rodwell, 
“to  comprehend  by  what  contortion  of  the  meaning  of  the  principal  passage 
quoted,  Swedenborg  can  be  supposed  to  allude  to  oxygen.  ‘Air,’  he  writes, 
‘consists  superficially  of  fifth  finites,  and  within  it  are  enclosed  the  first  and 
second  elementaries.’  And  again:  ‘The  fifth  finites  have  entered  into  the 
surface  of  the  aerial  particle,  and  the  first  and  second  elementaries  into  the 
internal  space.’  There  is  no  possible  reason  for  assuming  that  by  the  mean¬ 
ingless  term  ‘  fifth  finites  ’  oxygen  gas  is  alluded  to ;  and  if  there  w'ere  any 
evidence  at  first  sight,  it  would  be  speedily  nullified  by  the  fact  that  Swe¬ 
denborg  afterwards  speaks  of  crystals  of  tl.'s  matter.  It  is  useless  to  pursue 
the  subject  further:  the  only  evidence  in  . upport  of  the  supposition  is  so 
utterly  shallow  that  it  is  not  worthy  of  criticism,  for  it  carries  with  it  its  own 
refutation.” 

Dr.  Priestley  obtained  the  first  oxygen  produced  from  ’  red  precipitate,” 
(the  red  oxide  of  mercury)  by  heating  it  at  a  temperature  of  7520  F. — expressed 
in  symbols,  HgO — yield  Hg  +  O. 

Lavoisier,  in  his  “Elements  of  Chemistry,”  says  this  “species  of  air”  was 
discovered  about  the  same  time  by  Dr.  Priestley,  Mr.  Scheele,  and  “  myself' 

In  a  pamphlet  published  in  1800  by  Priestley,  after  his  return  to  America, 
he  says,  “  Having  made  the  discover)'  some  time  before  I  was  in  Paris  in  the 
year  1774,  /  mentioned  it  at  the  table  of  M.  Lavoisier,  when  most  of  the  phi¬ 
losophical  people  in  the  city  were  present,  saying  it  was  a  kind  of  air  in  which 
a  candle  burned  much  better  than  in  common  air,  but  I  had  not  then  given 
it  any  name.  At  this  all  the  company,  and  M.  and  Madame  Lavoisier  as 
much  as  any ,  expressed  great  surprise.  I  told  them  I  had  gotten  it  from  pre- 
cip'tate  per  se,  also  from  red  lead.  Speaking  French  very  imperfectly,  and 
being  little  acquainted  with  the  terms  of  chemistry,  I  said  plomb  rouge ,  which 
was  not  understood  until  M.  Macquer  said  I  must  mean  minium.  Mr.  Scheele’s 
discovery  was  certainly  independent  of  mine,  though,  1  believe,  not  made 
quite  so  early." 

Scheele  obtained  oxygen  from  one  of  the  minerals  of  his  own  country  as  he 
happened  to  be  investigating  the  nature  of  the  ores  of  mangarese. 

Lavoisier,  with  the  quickness  of  wit  belonging  to  his  countrymen,  does  not 
appear  to  have  been  slow  in  verifying  Priestley’s  experiment,  which  was  ana¬ 
lytical.  Great  credit  is  due  to  Lavoisier  for  reversing  Priestley’s  experiment, 
and  making  it  synthetical :  by  subjecting  a  given  quantity  of  air  to  the  action 
of  boiling  quicksilver,  he  made  that  which  Priestley  decomposed— viz.,  red 
precipitate. 


38 


594 


CHEMISTRY. 


The  latter  called  oxygen  Dephlogisticated  Air.  Lavoisier  gave  the  element 
a  name  which  has  remained,  like  an  official  registry  of  a  baptismal  name,  to 
the  present  time.  He  called  it  Oxygen  (o£vs  acid,  yevvacu  to  produce),  while 
others  styled  it  Empyreal,  or  Vital  Air. 

One  method  of  preparing  oxygen  gas  has  already  been  mentioned,  viz.,  that 
of  heating  the  red  oxide  of  mercury.  This  may  be  easily  done  in  a  test-tube, 
and  the  escape  of  the  oxygen  gas  is  soon  rendered  evident  by  a  splinter  of 
wood  inserted,  with  the  end  carbonized  and  just  red  hot  or  glowing,  which 
immediately  bursts  into  flame  with  a  sort  of  explosion,  and  then  burns  with 
great  brilliancy. 


Fig.  465. — A  Quicksilver  Lottie  of  wrought  iron , 
used  for  heating  the  black  Oxide  of  Manganese. 


With  respect  to  the  chemical  apparatus  that  may  be  described  in  this  sec¬ 
tion,  the  reader  is  recommended  to  go  to  Mr.  How,  Foster  Lane,  Cheapside, 
where  every  kind  of  chemical  apparatus  may  be  obtained. 

At  the  Polytechnic,  where  oxygen  is  used  in  very  large  quantities  for  the 
oxy-hydrogen  light,  it  is  made  by  heating  the  black  oxide  of  manganese,  Mn02, 
in  wrought-iron  bottles. 

Three  equivalents  of  Mn.Oa  yield  the  red  oxide  MnjCh  and  two  equivalents 
of  oxygen  gas.  The  plug  is  taken  out  of  the  iron  bottle,  and  an  iron  pipe 
screwed  into  it :  this  is  connected  with  a  large  flexible  tube,  and,  first  bubbling 
through  a  simple  washing  apparatus,  the  gas  passes  direct  to  a  large  copper 
gasometer.  Good  black  oxide  of  manganese  is  worth  about  £9  a  ton,  and 
should  yield  one-ninth  of  its  weight  of  oxygen  gas.  It  very  rarely  happens 
that  the  mineral  affords  more  than  half  that  quantity.  At  the  Polytechnic  an 
average  of  eight  tons  are  used  during  the  year ;  one-sixteenth  of  this,  viz.,  ten 
cwts.,  will  represent  the  weight  of  oxygen  used  in  that  establishment. 

On  the  small  or  the  large  scale,  where  cost  is  of  little  consequence,  oxygen 
is  readily  procured  by  heating  potassic  chlorate  (chlorate  of  potash),  not  alone, 
because  the  heat  softens  the  glass  vessel,  but  mixed  with  onc-third  or  one^ 


OXYGEN. 


595 


fourth  of  black  oxide  of  manganese.  The  oxygen  escapes  at  a  temperature 
of  450°  or  500°  F.,  and  the  black  oxide  of  manganese  undergoes  no  decom¬ 
position.  One  ounce  of  the  chlorate  will  yield  about  two  gallons  of  oxygen — 
2  KClOj  =  2  K  Cl  +  3  O*. 


Figs.  466,  467,  468. — A  Ring  Stand,  with  reducing  Porcelain  Ring , 
to  support,  if  necessary,  the  Ffask. 


The  flask  containing  the  chlorate  mixture  is  fitted  with  a  cork  and  bent  tube, 
and  heated  by  a  spirit-lamp,  or  by  any  of  the  convenient  gas-burners  which 
consume  mixed  air  and  coal-gas. 


Fig.  469. —  Various  Gas-burners  used  for  heating  purposes. 

A,  mixed  gas  and  air  burner,  with  wire  gauze  at  the  top  of  the  chimney,  c;  sheet-iron  case,  d,  for 
protecting  a  gas  or  spirit-flame  from  currents  of  air  and  economizing  heat;  b,  a  ring  perforated  with 
holes  for  burning  gas;  e,  rings  of  wire  for  reducing  the  si/e  of  the  large  rings  of  the  ring  stand,  in 
order  to  suppoit  smaller  vessels 


The  oxygen  gas  may  be  collected  in  jars  placed  upon  the  shelf  of  the  very 
convenient  tank  of  water  called  a  Pneumatic  Trough. 


38 —  2 


CHEMISTRY. 


596 


Ftg.  470. — A  Pneumatic  Trough.  Fig.  471. — Pneumatic  Trough  in  use. 


In  the  above,  Fig.  470,  another  box  is  provided,  to  receive  any  overflow  and 
to  prevent  the  slopping  of  water  on  the  table  where  the  experiments  are  con¬ 
ducted.  The  ordinary  pneumatic  trough,  with  the  gas-jars  on  the  shelf,  and 
the  flask  and  tube  or  retort,  containing  the  substance  yielding  gas,  is  shown  in 
Fig.  471. 

When  large  quantities  of  oxygen  are  required  for  the  oxy-hydrogen  lantern, 
the  gas  is  conveniently  and  quickly  made  from  the  chlorate  mixture  by  placing 
it  in  a  thin  sheet-iron  vessel  made  in  the  form  of  a  cone :  the  latter  can  be 
placed  over  a  larger  ring  of  burning  gas  or  on  an  open  fire;  and  by  taking 
the  precaution  to  pass  the  oxygen  first  through  a  wash-bottle  containing  a 
little  slaked  lime  and  water,  a  great  deal  of  the  chlorine  produced  from  the 
decomposition  of  the  pOtassic  chlorate  is  absorbed.  If  the  chlorine  be  not 


Figs.  472,  473. — Highlefs  arrangement  for  making  and  washing 

the  Oxygen  Gas. 


removed  with  lime,  or,  better  still,  with  potash,  it  soon  acts  upon  the  brass 
taps  fixed  into  the  caoutchouc  bags  ;  and  when — perhaps  at  a  critical  moment 
— a  good  light  is  wanted,  the  tap  is  stopped  up,  and  the  microscopic  slide  or 
the  magic  lantern  picture  is  badly  lighted. 

In  the  article  on  the  dissolving  view  apparatus,  Messrs.  C.  and  F.  Darker,  of 


OXYGEN. 


597 


Paradise  St.,  Lambeth,  have  been  recommended  for  all  apparatus  of  that  kind ; 
and  another  simple  arrangement  of  a  thin  sheet-iron  or  copper  bottle  contain¬ 
ing  the  chlorate  mixture,  attached  by  flexible  tubes  to  a  simple  washing  appa¬ 
ratus  made  with  a  corked  bottle,  into  which  the  pipe  from  the  generator  dips, 
with  a  delivery-pipe  passing  to  an  india-rubber  bag,  is  shown  at  Fig.  474. 

There  are  many  other  ways  in  which  oxygen  can  be  made,  all  detailed  in 
works  devoted  to  chemistry,  such  as  Dr.  Miller’s  “Elements  of  Chemistry,” 
or  Abel  and  Bloxam’s  “  Handbook.” 


The  Properties  of  Oxygen. 


The  specific  gravity  of  this  gas  is  rio563:  it  is  perfectly  tasteless,  odour¬ 
less,  and  colourless,  and  has  never  been  reduced  by  extreme  cold  or  great 
pressure  into  the  liquid  or  solid  condition ;  oxygen  is  therefore  said  to  be  a 
permanent  gas.  With  the  exception  of  fluorine,  oxygen  unites  with  every 
other  known  element. 

Charcoal,  sulphur,  phosphorus,  many  of  the  metals,  such  as  iron,  zinc,  pot¬ 
assium,  and  sodium,  burn  in  this  gas  with  great  brilliancy,  forming  acids, 
oxides,  and  alkalies. 

The  act  of  dissolving  a  metal  in  nitric  acid  is  called  oxidation,  the  acid 
yielding  oxygen  to  the  metal,  which  oxide  afterwards  unites  with  another 
portion  of  the  acii. 

Liquid  red  hot  nitre  acts  as  a  powerful  oxidizer,  in  which  the  hardest  form 
of  carbon,  viz.,  the  diamond,  is  readily  oxidized  and  dissolved,  by  forming 
carbonic  anhydride,  which  unites  with  the  dipotassic  oxide  or  potash — KaO. 


Fig.  474, —  Gas  Generator ,  Spirit-lamp ,  Ring  Stand ,  Wash  Bottle, 

and  Gas-bag. 


598 


CHEMISTR  Y. 


One  hundred  cubic  inches  of  oxygen,  at  6o°  and  30  in.  barometer,  weigh 
34-203  grains.  Water  dissolves  a  small  volume  of  oxygen  gas. 

100  volumes  of  water  dissolve  4'ii  volumes  of  oxygen  at  32°  F. 

100  „  „  2-99  „  „  59°  „ 

Remarks. 

It  has  been  ascertained  that  oxygen  possesses  weak  but  decidedly  magnetic 
properties,  like  those  of  iron,  liable  to  diminution  or  increase  by  raising  and 
lowering  the  temperature.  Oxygen  is  a  dyad,  as  in  H20,  in  common  with 
sulphur,  selenium,  and  tellurium. 

The  atomic  weight  of  oxygen  is  now  taken  as  16  instead  of  8,  so  that  water 
is  represented  by  the  formula  H20  =  i8  instead  of  9. 

Oxygen  represents  nearly  one-fifth  of  the  bulk  of  the  atmosphere,  the  com¬ 
ponent  parts  of  which  will  be  considered  hereafter. 

Every  nine  pounds  of  water  contain  eight  of  oxygen. 

Nearly  half  the  weight  of  dry  sand  and  clay  consists  of  oxygen. 

The  vital  functions  cannot  be  maintained  without  oxygen,  and  by  a  species 
of  slow  combustion,  or  oxidation  of  the  blood  through  the  ramifications  of  the 
lung  process,  heat  is  slowly  produced;  and  that  a  new  product  is  formed  is 
shown  by  the  quantity  of  caibonic  anhydride  expired  with  the  breath,  and  the 
change  of  the  dusky  purple  or  dark  blood  to  bright  crimson. 

There  is  no  gaseous  body  more  serviceable  and  important  to  man,  or  any  j 
element  which  has  helped  to  increase  the  industrial  wealth  of  this  country  , 
so  much  as  oxygen. 

The  various  compounds  it  forms,  such  as  oxides,  acids,  basic  oxides,  alka-  j 
lies,  and  saline  oxides,  will  be  referred  to  in  other  places. 

The  tests  for  oxygen  are  combustion  with  hydrogen  and  formation  of  water.  | 

The  change  of  colour  when  a  solution  of  pyrogallic  acid  in  potash  is  shaken  : 
with  oxygen. — The  solution  of  potash  alone  will  not  dissolve  oxygen,  but  the  i 
pyrogallic  acid  determines  the  rapid  absorption  of  this  gas  and  turns  a  dark 
brown  colour. 

A  mixture  of  colourless  nitric  oxide  gas,  NO,  with  oxygen,  forms  red  fumes, 
which  are  readily  soluble  in  water. 

Ozone. 

Although  oxygen  has  never  been  changed  from  the  gaseous  state  to  a  liquid 
or  solid  condition,  it  seems  to  be  capable  of  assuming  a  peculiar  condensed  j 
form  called  Ozone,— a  word  taken  from  the  Greek  o£w,  to  give  out  an  odour. 

MM.  de  Babo,  Claus,  and  Soret  all  maintain  that  ozone  is  oxygen  denser  j 
than  common  oxygen  gas.  The  latter  philosopher  especially  declared  that 
ozone  as  a  molecule  consisted  of  three  atoms  of  oxygen,  and  he  therefore  called 
it  binoxide  of  oxygen.  M.  Soret,  in  continuation  of  his  researches  on  the  ! 
density  of  ozone,  and  employing  the  absorptive  powers  of  essences  of  turpen¬ 
tine  and  cinnamon,  has  come  to  the  conclusion  that  the  density  of  ozone  is  1-^ 
times  that  of  oxygen,  and  gives  as  the  formula  for  ozone  b3.  Other  learned 
chemists  appear  to  concur  in  this  opinion. 

Ozone  is  p’roduced  in  various  ways. 

1.  By  passing  a  series  of  electrical  discharges — -silent  ones  —  through  dry 
oxygen  gas:  the  latter  diminishes  in  bulk  to  the  extent  of  one-twelfth,  show¬ 
ing  condensation;  and  if  subsequently  heated  to  a  temperature  of  550°  F.,  re- 


OZONE. 


599 


covers  its  fonner  bulk  and  loses  its  peculiar  ozone  qualities.  The  reason  the 
electrical  discharge  should  be  a  silent  one  is  because  the  electrical  spark  pro¬ 
duces  too  much  heat,  which  destroys  a  considerable  portion  of  the  ozone,  and 
thus  prevents  any  considerable  accumulation.  At  p.  388  Siemen’s  apparatus 
is  described  (an  induction  apparatus),  by  which  large  quantities  of  oxygen 
may  be  converted  into  ozone. 

2.  This  peculiar-  condition  of  oxygen  is  obtained  by  acting  either  on  pot¬ 
assium  permanganate  (KMnO,)  or  upon  baric  dioxide  (Ba02)  with  strong  sul¬ 
phuric  acid. 

3.  A  stick  of  phosphorus  scraped  clean  under  water,  and  then  exposed  in  a 
bottle  containing  moist  air,  produces  ozone. 

4.  When  water  is  decomposed  in  the  apparatus  called  a  voltameter,  the 
mixed  gases  give  the  peculiar  odour  and  are  found  to  contain  a  certain  quantity 

of  ozone. 

The  best  tests  for  this  condensed  form  of  oxygen  are  potassium  iodide,  and 
starch  paste  painted  with  a  brush  on  paper,  or  paper  dipped  in  a  solution  of 
sulphate  of  manganese,  MnS04  +  5H20.  The  first  turns  blue  from  the  libe¬ 
ration  of  iodine  and  the  formation  of  a  blue  compound  of  starch  and  iodine; 
and  the  second  indicates  the  presence  of  ozone  by  the  formation  of  the  brown 
hydrated  peroxide  of  manganese. 

Schoenbein,  who  first  directed  attention  to  this  allotropic  condition  of  oxy¬ 
gen,  directs  the  test-paper  to  be  made  of  a  fixed  strength,  by  dissolving  one 
part  of  pure  potassic  iodide  in  200  parts  of  distilled  water,  which  is  then  to  be 
thickened  by  heating  it  with  10  parts  of  starch.  This  solution  is  to  be  applied 
to  bibulous  paper,  which,  when  dry,  should  be  kept  in  a  stoppered  bottle  covered 
with  tin  foil,  in  order  to  exclude  the  light. 

It  is  known  that  sea-air  contains  ozone,  whilst  the  same  air,  having  passed 
over  or  through  a  town,  is  supposed  to  be  deprived  in  a  great  degree  of  this 
agent,  which  is  considered  to  have  purifying  and  health-giving  powers.  The 
absence  of  ozone  from  the  air  is  said  to  be  prejudicial  to  health,  and  during 
the  prevalence  of  cholera  it  was  thought  to  be  due  in  some  degree  to  the 
absence  of  this  condition  of  oxygen. 

Dr.  Daubeney  found,  in  the  three  winter  months  commencing  with  January, 
at  Torquay,  that  the  south-west  and  westerly  winds  were  most  fully  charged 
with  ozone,  whilst  the  north  winds  showed  the  least.  On  the  contrary,  at  Ox¬ 
ford  during  the  summer  months  of  the  same  year,  the  easterly  winds  were 
most  charged  with  ozone,  and  the  north-westerly  the  least.  These  indications 
clearly  pointed  to  the  influence  of  the  sea  in  augmenting  the  amount  of  ozone 
at  Torquay,  whilst  the  more  central  inland  position  of  Oxford  caused  the  dif¬ 
ference  between  the  maximum  and  minimum  indications  to  be  much  less 
apparent  than  at  the  sea-side.  Daubeney  also  found  that  plants  growing  in 
the  sunshine  liberate  a  body  that  affects  the  starch  test  like  ozone,  and  hence 
inferred  that  this  remarkable  property  of  plants  might  have  something  to  do 
with  the  maintenance  of  the  healthiness  and  purity  of  the  air. 

Ozone  possesses  most  energetic  qualities.  It  sets  free  iodine  from  its  com¬ 
bination  with  the  metals.  Black  sulphide  of  lead  or  plumbic  sulphide  (PbO) 
is  attacked  by  ozone;  the  black  stain  disappears,  and  both  the  sulphur  and 
the  lead  oxidize,  the  white  sulphate  of  lead  (PbS04)  being  produced.  Ozone 
is  a  powerful  bleaching  agent:  it  irritates  the  lungs  if  inhaled  in  any  quantity; 
and  this  is  not  surprising  when  it  is  remembered  that  both  cork  and  caout¬ 
chouc  are  not  proof  against  its  oxidizing  power.  Silver,  which  resists  common 


6oo 


CHEMISTRY. 


oxygen,  and  is  so  often  used  in  chemical  processes  for  this  reason,  is  converted 
into  peroxide  when  exposed  to  the  action  of  ozone,  provided  that  the  presence 
of  moisture  is  secured. 

Ozone  is  now  introduced  into  certain  chemical  processes,  and  is  likely  to 
take  a  very  prominent  place  as  one  of  the  oxidizers,  the  wealth-producers  in 
refining  sugar,  bleaching  calico,  &c. 


- ♦ - 

NITROGEN. 

Symbol,  N.  Atomic  weight,  14. 

N  itrogen  is  described  in  an  old  work  as  “  a  simple  oxidable  body,  by  some 
chemists  called  azot,  from  its  property  of  destroying  life.  This  name  appears 
improper,  since  several  other  gases  have  the  same  effect  on  animals.”  It  was 
discovered  by  Dr.  Rutherford  in  the  year  1772,  and  was  called  Nitrogen  from 
1  irpov  nitre,  and  yevvao)  to  generate. 

It  would  be  difficult  to  speak  of  nitrogen  without  alluding  to  the  important 
part  it  takes  in  the  composition  of  the  atmosphere.  Rodwell  says,  from  the 
continued  observation  that  the  cessation  of  breathing  was  the  cessation  of 
life,  the  belief  became  prevalent  that  the  soul  passed  from  the  body  with  the 
last  expiration  of  air;  hence  the  expressions,  “  Efflare  animam,”  “  Exhalare 
animam,”  “  Expiram  animam.”  Again,  irvexi/xa,  spirit  us ,  anima ,  have  each 
the  triple  meaning  of  soul ,  breath ,  wind.  There  is  also  a  Hebrew  word  having 
the  same  meaning  as  the  Greek  pneuma,  viz.,  soul,  breath,  wind.  The  most 
convenient  mode  of  preparing  nitrogen  is  by  removing  the  oxygen  from  atmo¬ 
spheric  air,  and  when  this  is  done  it  is  found  that  it  constitutes  four-fifths  of 
any  given  bulk.  A  variety  of  processes  may  be  employed  for  this  purpose, 
but  the  simplest  plan  is  to  place  some  dry  phosphorus  in  a  German  porcelain 
cup,  and  having  properly  supported  it  on  the  shelf  of  the  pneumatic  trough,  a 
long  unstoppered  gas-jar  graduated  into  five  equal  parts  is  placed  over  the 
whole ;  a  heated  wire  is  now  inserted,  and  directly  it  touches  the  phosphorus, 
the  latter  ignites,  and  the  stopper  of  the  jar  is  quickly  inserted.  At  first  ex¬ 
pansion  occurs,  and  therefore  the  depth  of  water  should  be  adjusted  before¬ 
hand,  so  as  to  allow  the  heated  air  to  increase  in  volume  without  bubbling  out 
and  escaping  from  the  bottom  of  the  jar. 

If  the  above  manipulations  are  skilfully  performed,  very  little  air  is  lost: 
the  phosphorus  burns,  producing  the  white  fumes  of  phosphoric  pentoxide, 
which  gradually  subside,  and  are  dissolved,  by  the  water.  The  residual  gas, 
when  cold,  is  found  to  be  equal  to  four-fifths  of  the  original  bulk,  one-fifth — 
viz.,  the  oxygen — being  removed  by  combining  with  the  phosphorus. 

The  same  result  is  more  accurately  obtained  by  thrusting  up  into  a  gradu¬ 
ated  tube  containing  atmospheric  air  a  piece  of  phosphorus  supported  in  a 
coil  of  platinum  wire:  after  two  or  three  days  the  phosphorus  may  be  removed, 
and  the  remaining  gas  is  found  to  be  nearly  pure  nitrogen;  and  if  100  mea¬ 
sures  of  air  be  used,  20  will  be  removed  and  80  left. 

Another  mode  of  preparing  nitrogen  is  by  passing  air  over  finely  divided 
metallic  copper  at  a  red  heat.  The  experiment  conducted  by  Dumas  and 
Boussingault  was  performed  by  them  with  great  precautions  in  the  exact 
analysis  of  air,  and  they  found  that  ioo  parts,  by  weight,  of  air  from  which 
the  aqueous  vapour,  carbonic  anhydride,  and  ammonium  had  been  removed, 


BACTERIA. 


601 


contained  77  parts  of  nitrogen  and  23  parts  of  oxygen  ;  or,  more  precisely, 
taking  the  average  of  a  number  of  experiments,- — 

Weights.  Volumes. 

Nitrogen  ....  76-99  79- 19 

Oxygen  ....  23-01  2081 


IOO'OO  too  co 

Lately  thc“  Bacteria,”  or  minute  organisms  contained  in  common  air,  have 
been  carefully  examined  and  experimented  on  by  Professor  Tyndall,  and  his 
experiments  are  thus  graphically  described  by  a  press  writer,  signing  himself 
“  Warder,”  in  answer  to  the  question,  “  What  are  Bacteria?”  : 

Bacteria,  since  the  word  has  found  its  way  into  no  dictionary,  are  the 
minute  organisms,  wholly  invisible  to  the  naked  eye,  which  are  the  cause  of 
all  putrefaction.  Place  a  drop  of  the  juice  of  a  putrid  chop  under  a  powerful 
microscope,  it  is  seen  to  be  swarming  with  minute  but  extremely  animated 
organisms,  which  are  the  cause  of  all  decay  and  putrefaction.  Keep  meat 
or  any  other  similar  matter  from  these,  and  it  will  remain  Sweet ;  so  soon  as 
they  obtain  access,  the  process  of  corruption  begins.  Not  easy  is  it  to  keep 
these  voracious  creatures  from  that  which  is  their  prey  ;  but  it  is  to  be  done, 
and  when  we  have  learned  to  do  it,  a  complete  revolution  in  the  economic 
history  of  society  may  be  expected. 

That  these  bacteria  are  not  spontaneously  generated,  it  is  the  object  of 
Professor  Tyndall  to  show.  He  proves  this  truth  by  an  illustration  which 
will  come  home  to  most  of  us.  There  are  few  of  us  who  have  not  at  some 
time  or  other  been  into  a  darkened  chamber,  into  which,  through  some  chink 
or  aperture,  darts  a  ray  of  sunlight.  At  first  this  ray  is  distinctly  visible,  its 
effect  being  shown  upon  the  floating  dust  of  the  atmosphere.  If  perfect  still¬ 
ness  is  maintained,  and  the  atmospheric  dust  is  allowed  to  settle,  the  luminous 
track  will  grow  “  fainter  and  fainter,  until  at  last  it  disappears  absolutely,  and 
no  trace  of  the  beam  is  to  be  seen.”  In  this  dust,  the  presence  of  which  is 
thus  manifested,  float  the  most  potent  of  known  agents  of  that  change  we  call 
destruction.  The  experiments  the  professor  describes  prove  this  to  demon¬ 
stration.  Expose  a  number  of  vessels  containing  beef-tea  to  the  motionless 
air  of  a  chamber  that  has  become  stilled,  and  let  no  disturbance  approach 
them.  At  the  end  of  three  months  or  three  years  the  contents  will  be  found 
as  sweet  and  clear  as  the  day  when  they  were  first  put  in.  If,  however,  at 
the  same  time,  you  put  unequal  number  of  vessels  containing  the  same  liquid 
into  a  room  in  which  the  atmosphere  is  dust-laden,  in  three  da\  s  the  whole  01 
the  vessels  stink,  and  the  contents  are  found  to  be  swarming  with  bacteria. 
You  can  multiply  these  experiments  ad  infinitum,  and  with  the  same  results. 
In  place  of  the  beef-tea,  you  can  put  “every  imaginable  infusion  of  wild 
animals  or  tame  ;  of  flesh,  fish,  fowl,  and  viscera,  of  vegetables  of  the  most 
various  kinds.  The  result  will  be  always  the  same  :  the  infusion  in  the  tran¬ 
quil  chamber  will  remain  sweet  and  free  from  bacteria,  those  in  the  dust¬ 
laden  atmosphere  will  at  once  pass  through  all  processes  of  decay.” 

Little  is  as  yet  known  of  the  origin  of  these  agents  of  decay.  We  know 
that  warmth  is  favourable  to  their  development,  that  a  certain  amount  of 
heat  kills  them,  and  that  cold  deadens  them.  We  have  hitherto  acted  upon 
an  empirical  observation,  which  has  been  sound  and  accurate  enough  so  far 
as  it  has  gone.  We  have  kept  flesh,  game,  and  all  things  most  liable  to 


602 


CHE  MIS  TR  V 


decay  in  cool  cellars  seldom  entered,  and  have  sometimes  inserted  metal 
windows,  perforated  with  small  holes,  which  would  necessarily  let  in  few  of 
the  germs  of  mischief.  Our  fishmonger  has  learned  to  surround  his  fish  with 
lumps  of  ice,  and  by  thus  arresting  the  operation  of  the  bacteria  and  chilling 
them  into  numbness,  obtains  a  longer  period  during  which  his  “very  assail¬ 
able  wares”  remain  fresh  and  saleable.  In  the  reverse  manner  the  house¬ 
keeper  boils  her  milk,  so  destroying  the  infant  bacteria,  or  partially  cooks  the 
pheasant  when  she  detects  signs  of  incipient  putrefaction.  Proofs  how  far 
the  action  of  cold  extends  are  afforded  by  Professor  Tyndall,  who  states  that 
the  bodies  of  those  who  have  been  lost  in  the  crevasses  of  the  Alpine  glaciers 
have  been  recovered  after  an  interval  of  forty  years,  and  have  been  found  to 
display  no  traces  of  putrefaction.  A  more  remarkable  case  still  is  offered  by 
the  discovery  in  the  snows  of  Siberia  of  the  body  of  a  hairy  elephant  that  had 
been  buried  for  ages.  As  it  was  encased  in  ice  the  flesh  remained  sweet,  and 
for  some  time  afterwards  “  afforded  copious  nutriment  to  the  wild  beasts 
which  fed  upon  it.” 

It  is  apropos  of  beer  that  the  lecturer  commences  his  warning.  Keep 
the  bacteria  out  of  beer,  and  it  remains  for  ever  unaltered.  Without  their 
presence  it  will  never  contract  disease.  The  aim  of  the  brewer  has  long  been 
to  paralyse  them.  These  germs  are,  however,  in  the  air— in  the  vessels  he 
employs  in  the  brewery,  in  the  yeast  used  to  impregnate  the  wort.  Here,  as 
in  other  matters,  temperature  is  an  all-important  point,  and  the  beers  brewed 
at  low  temperatures  are  rapidly  driving  all  others  out  of  the  market.  Hop, 
however,  is  to  some  extent  an  antiseptic  to  beer.  The  essential  oil  of  the  hop 
is  bactericidal — hence  the  strong  impregnation  with  hop-juice  of  all  beer  in¬ 
tended  for  exportation.  Wine,  again,  is  subject  to  like  influences.  The  fer¬ 
mentation  of  wine  is  attributable  to  the  torula,  a  species  of  vegetable  growth 
which  has  been  the  subject  of  close  investigation  by  a  Frenchman  named 
Pasteur,  whose  conclusions  Professor  Tyndall  gives  to  the  world.  These 
things  all  point  a  lesson  which  the  lecturer  thus  phrases — “  Thus  we  begin  to 
see  that  within  the  world  of  life  to  which  we  ourselves  belong  there  is  another 
living  world  requiring  the  microscope  for  its  discernment,  but  which,  never¬ 
theless,  has  the  most  important  bearing  on  the  welfare  of  the  higher  life 
world.” 

inow,  there  are  two  great  purposes  to  which  for  our  social  benefit  we  can 
turn  the  discoveries  with  which  I  have  been  dealing.  Some  steps  have 
been  taken  in  the  direction  of  both.  Science  is  as  yet  at  the  threshold  of 
discovery,  but  very  practical  results  may  soon  be  expected.  This  theory 
of  fermentation  to  which  Dr.  Tyndall  refers  applies  also  to  many  forms  of 
disease.  So  soon  as  the  bacteria  gets  in  a  wound,  it  produces  what  is  called 
festering.  Hence  empirical  science  long  ago,  while  ignorant  of  the  cause, 
bandaged  a  cut  finger  so  that  the  air  should  not  get  to  it.  The  aim  of  our 
surgical  experts  is  now  to  kill  the  bacteria,  which  yield  easily  to  some  things, 
and  especially  to  diluted  carbolic  acid.  Hence  has  arisen  the  antiseptic 
treatment  in  surgery,  the  effect  of  w'hich  is  said  to  be  one  of  the  strongest 
steps  in  advance  that  surgery  has  ever  made.  Fevers,  however,  and  other 
diseases  of  the  kind,  are  similar  in  origin.  The  virus  of  small-pox  is  a 
seed.  “It  is  sown  as  yeast  is  sown  (in  brewing);  it  grows  and  multiplies 
as  yeast  grows  and  multiplies,  and  it  always  reproduces  itself that  is  to 
say,  it  does  not  change  into  another  species  of  ferment.  As  he  touches  here 
on  medical  science,  Tyndall  stops  short,  saying  that  it  is  shown  almost  to 


BACTERIA. 


603 


demonstration  that  epidemic  diseases  spring  from  reproductive  parasitic  life 
that,  living,  ferments,  increases,  and  multiplies  on  the  body.  In  some  forms 
of  disease  to  which  animals  are  subject — as,  for  instance,  in  splenic  fever — 
the  investigations  have  reached  a  point  at  which  the  source  of  contagion  is 
traced,  and  the  stamping  out  the  disease  is  a  npitter  of  certainty.  The  con¬ 
clusion  Professor  Tyndall  arrives  at  is  that  the  ravages  of  war  tenfold 
multiplied  would  prove  “evanescent  as  compared  with  the  ravages  due  to 
atmospheric  dust.”  From  the  ground  we  have  won  the  professor  looks  forward 
to  future  victories  over  disease.  I  should  like  to  say,  carry  lurthcr  your  ex¬ 
periments  with  the  microscope.  Is  it  not  possible  that  rabies  is  due  to  similar 
causes?  Does  the  poison  of  the  snake  depend  upon  any  similar  principle? 
Is  not  decay  in  teeth  very  probably  the  result  of  some  species  of  fungoid 
deposit  which  may  be  killed  as  easily  as  the  bacteria  ?  These  questions  I  can 
only  in  my  ignorance  throw  out.  Meanwhile,  if  we  can  kill  the  bacteria— and 
it  seems  as  if  the  means  were  within  our  reach — what  is  to  prevent  us  from 
importing  all  the  meat  we  require  from  the  countries  in  which  it  abounds? 
Why  should  not  countries  like  Britain,  whose  population  is  so  rife,  give  up 
the  attempt  at  cattle  breeding,  and  import  all  the  meat  they  require  fresh  from 
the  prairie  or  the  pampas?  Such  dreams  may  seem  visionary,  but  they  are 
not  so  unless  science  is  misleading  us.  If  I  mistake  not,  we  are  at  the  com¬ 
mencement  of  a  new  era  in  the  treatment  of  disease  and  in  the  management 
of  our  food  supply.  Even  if  I  am  too  sanguine,  good  has  already  come  of  the 
discovery  that  has  been  made.  Professor  Tyndall  lias  done  high  service  in 
bringing  such  matters  within  the  general  ken,  for  the  co-operation  of  the 
public  will  have  to  be  called  for,  and  the  public  mind  may  with  advantage  be 
prepared  for  what  will  soon  be  asked  of  it. 

In  further  proof  of  the  existence  of  organic  matter  in  air,  Professor  Miller 
remarks  that  if  air  which  has  been  scrupulously  freed  from  carbonic  acid  gas 
is  passed  over  a  column  of  pure  ignited  black  oxide  of  coppeij  traces  of  car¬ 
bonic  acid  are  always  obtained,  owing  to  the  oxidation  of  some  combustible 
compound  of  carbon.  In  the  junctions  of  the  apparatus  employed  for  this  ex¬ 
periment,  the  use  of  cork  and  caoutchouc  must  be  avoided  (Karsten),  or  other¬ 
wise  the  carbonic  acid  might  be  derived  from  them.  Miller  also  states  that 
the  following  are  the  results  of  some  of  the  most  trustworthy  experiments 
upon  the  weight  of  air  calculated  from  the  experiments: 


Of  Dumas  and  Boussingault 
Of  Biot  and  Arago 
Of  Prout 
Of  Regnault 


The  second  result  is  probably  the  most  accurate,  for  it  exactly  corresponds 
with  tire  density  deduced  from  that  of  a  mixture  of  oxygen  and  nitrogen  in  the 
proportions  in  which  they  occur  in  die  atmosphere. 

A  cubic  metre  of  air,  according  to  this  result.  ato°C.  and  760  mm.  pressure, 
weighs  1  '299 1  kilogrammes,  or  a  cubic  foot  under  a  pressure  of  30  inches  bar. 
weighs  536  96  grams  at  6o°.  The  weight  of  a  given  volume  of  air  at  6o°  F., 
under  a  pressure  oi  30  inches  bar.,  is  therefore  only  S},T  of  that  of  an  equal 
bulk  of  water  at  the  same  temperature,  or  at  o°  C.  and  760  mm.  barome¬ 
tric  pressure. 


604 


CIIEM1STR  Y. 


Formerly  the  symbol  for  oxygen  was  taken  as  0  =  8,  and  the  volume  occu¬ 
pied  by  8  parts  by  weight  of  oxygen  was  taken  as  the  unit  pf  gaseous  volume. 

Jf  the  atomic  weight  of  oxygen  be  represented  as  0  =  i6,  the  molecule  of 
the  free  oxygen  will  be  (00),  with  a  molecular  weight  =  32  and  molecular 
volume  |  |  |  ;  the  atomic  weight  of  hydrogen  being  (H  •  1),  the  molecule  of 
free  hydrogen  will  be  (HH),  occupying  the  same  volume  as  a  molecule  of 
oxygen;  and  the  molecular  weight  of  water  will  be  H.,0=i8,  instead  of 
HO =9. 

Nitrogen  has  no  colour,  taste,  or  smell.  It  is  lighter  than  oxygen  gas,  and 
slightly  lighter  than  atmospheric  air:  100  cubic  inches  at  6o°  F.,  30  in.  bar., 
weigh  30'H9  grains.  A  lighted  taper  immersed  in  this  gas  is  immediately 
extinguished,  no  incandescent  snuff  remaining.  It  must  not,  however,  be  sup¬ 
posed  that  nitrogen  is  poisonous:  it  simply  destroys  life  in  the  absence  of 
oxygen  gas,  and  cannot  be  poisonous,  or  we  could  not  continue  to  breathe  air, 
which  is  a  mechanical  mixture  of  the  two  gases  always  maintained  in  the  same 
relative  volumes  by  one  of  those  wonderful  conservative  powers  of  Nature  re¬ 
presented  by  the  vegetable  kingdom.  Although  the  two  gases  differ  in  weight, 
they  never  separate ;  and  by  the  law  of  the  universal  diffusion  of  gaseous 
bodies,  they  have  the  power  of  incorporating  perfectly  with  each  other  ;  and 
this  property  of  gases  in  general,  and  specially  in  this  case,  has,  no  doubt, 
the  most  important  bearing  on  the  purity  and  healthiness  of  the  air.  No  com¬ 
bination  occurs  between  the  oxygen  and  nitrogen  contained  in  atmospheric 
air,  although  it  is  quite  possible  to  conceive  that  where  ozone  is  produced  in 
hot  climates  with  certain  peculiarities  of  soil — as  in  Spain,  Egypt,  and  India 
—  that  there  the  nitrogen  is  attacked  by  the  condensed  oxygen  ozone,  and 
nitrates  produced. 

Professor  Graham  has  shown  that  the  velocity  of  the  diffusion  of  the  various 
gases  is  in  the  inverse  ratio  of  the  square  roots  of  their  densities;  and,  as 
before  stated,  this  principle  of  diffusion  explains  why  the  composition  of  100 
parts  by  volume  of  the  air  may  be  taken  at  an  average  as  follows : 


Country 

air. 


Town 
air  also 


Nitrogen . 

•  77'95 

Oxygen . 

20-6 1 

Carbonic  anhydride  (carbonic  acid) 

•04 

Aqueous  vapour . 

Hydric  nitrate  (nitric  ackP 

.  i'4o 

■) 

Ammonia  ...... 

Carburetted  hydrogen  ... 

Sulphuretted  hydrogen  .  .  )  . 

Sulphurous  anhydride  .  .  )  iaces- 

.  > traces 

IOO'OO 

HYDROGEN. 

Symbol,  H.  Atomic  weight,  1. 

Although  this  article  on  Chemistry  must  necessarily  be  confined  to  certain 
limits,  and  therefore  the  various  compounds  formed  by  the  combination  of  the 
different  elements  cannot  all  be  considered,  exceptions  to  this  rule  must  occa¬ 
sionally  be  made ;  and  having  considered  the  chemical  nature  of  air,  it  would 
be  hardly  possible  to  avoid  making  some  remarks  on  the  constitution  of  water, 
the  more  so  as  this  is  the  chief  source  from  which  hydrogen  is  obtained. 


WATER . 


605 


Water  is  presented  to  us  in  nature  having  different  degrees  of  purity;  hence 
tve  speak  of  hard  or  soft  water.  The  former  may  contain  calcium  carbonate 
and  sulphate,  magnesium  carbonate  and  sulphate,  sodium  sulphate  and  chlo¬ 
ride,  and  many  other  substances,  in  considerable  quantities,  especially  if  the 
water  flowing  into  the  well  be  derived  chiefly  from  surface  drainage.  When 
the  water— such  as  rain-water — has  been  collected  after  several  hours’  rain, 
it  is  almost  in  a  state  of  purity,  containing  then  only  certain  gaseous  matters 
in  solution:  such  water  is  usually  called  soft,  because  it  is  free  from  the  salts 
already  mentioned.  If  the  rain-water  be  collected  after  a  long  drought,  it  may 
then  contain  nitrates  and  salts  of  ammonium,  and,  if  near  the  sea-side,  would 
always  contain  sodium  chloride  or  common  salt. 

River-water  usually  comes  under  this  denomination,  because  it  contains  a 
less  proportion  of  saline  matters  in  solution:  it  is  not,  however,  so  good  to 
drink  as  spring-water,  because  it  frequently  occurs  that  rivers  receive  the 
sewage  of  large  towns,  and  hence  the  water  contains  organic  matter  in  solu¬ 
tion,  and,  should  the  water  be  taken  whilst  this  organic  matter  is  undergoing 
decomposition,  very  serious  consequences  may  result  to  the  person  drinking 
it.  It  is  now,  however,  a  rule  in  sanitary  matters  to  endeavour  to  divert  the 
sewage  from  our  noble  rivers  when  possible,  and  with  the  help  of  proper  filters 
the  Thames  water  is  now  potable  and  wholesome. 

All  rivers  flow  into  the  sea,  hence  sea-water  contains  a  larger  quantity  of 
sodium  chloride,  and  many  other  salts,  in  solution,  likewise  organic  matter; 
but,  curious  to  say,  it  remains  in  a  uniform  condition  so  far  as  the  quantity 
of  saline  matter  is  concerned,  and  the  specific  gravity  varies  little,  the  mean 
being  1,027,  pure  water  being  i,ooo. 

When  sea-water  or  any  other  hard  water  is  placed  in  a  still  and  boiled,  the 
earthy  or  saline  matters  are  left  behind,  and,  the  steam  only  being  condensed, 
pure  water  is  obtained. 


Fig.  475. — The  Still  placed  on  a  common  fire  or  fitted  to  a  proper  furnace. 

Both  the  stills  have  worm  tub>  or  condensers. 


The  operation  of  distilling  may  be  performed  on  a  vyry  small  scale  by  using 
a  little  flask  fitted  into  a  bent  tube,  which  is  placed  in  a  basin  containing  cold 
water  (Fig.  476).  Very  convenient  little  tin  or  copper  stills  are  made  by  Mr.  How, 
of  Foster  Lane,  Cheapside:  they  are  heated  by  a  Bunsen  burner,  and  will  supply 
a  sufficient  quantity  of  fresh  distilled  water  for  any  analytical  operations  con- 


6o6 


CHEMISTRY. 


ducted  on  a  moderate  scale,  and, 
with  a  very  little  attention  and  a 
small  consumption  of  gas,  they  will 
readily  yield  a  Winchester  quart  of  * 
distilled  water  per  diem. 

Water  when  absolutely  pure  has 
no  taste  or  smell,  is  free  from 
colour,  except  when  examined  in 
particular  thicknesses,  and  per¬ 
fectly  transparent. 


Fig.  477. — Small  Tin  or  Copper  Still ,  with 
Worm  Tubs ,  to  be  heated  by  Gas. 


Fig.  478  — Useful  Vessels  called 
Beakers ,  in  which  Solutions 
are  prepared. 


It  is  invaluable  as  a  solvent,  and  no  laboratory  is  complete  without  a  proper 
supply  of  it  stored  in  well-stoppered  bottles. 

Pure  water  is  the  standard  to  which  the  specific  gravities  of  other  liquids 
and  solids  are  referred. 

Under  the  ordinary  pressure  of  the  air,  it  boils  at  21 2°  F.  If,  however,  it  be 
confined  in  a  very  strong  wrought-iron  vessel,  such  as  the  apparatus  called  a 

Papin’s  digester,  the  boiling-point  is  raised,  and,  as 
the  steam  does  not  escape,  the  solvent  powers  of  the 
water  are  greatly  increased.  Water  has  in  this  way 
been  raised  to  the  temperature  of  4190  F.,  and  Mus- 
chenbroek  stated  that  he  had  made  water  hot  enough 
in  a  Papin’s  digester  to  melt  tin. 

The  chemical  composition  of  water  may  be  deter¬ 
mined  analytically  or  synthetically.  In  the  article 
on  voltaic  electricity  it  has  been  shown  that  water, 
when  subjected  in  a  proper  manner  to  a  current  of 
electricity,  is  decomposed  into  oxygen  and  hydrogen, 
and  if  they  are  collected  in  separate  tubes,  the  latter, 
eliminated  at  the  platinode  or  negative  platinum 
plate,  is  found  to  be  double  the  volume  of  the  oxygen 
set  free  at  the  zincode  or  positive  plate.  Thus  the 
composition  of  water  is  shown  to  be  in  the  propor¬ 
tion  of  two  measures  of  hydrogen  with  one  of  oxy¬ 
gen.  According  to  modern  views,  the  atomic  con¬ 
stitution  of  water  is  represented  by  the  formula  H20 
=  18,  instead  of,  as  formerly,  HO=9. 


Fig.  479. 

A  Papin’s  Digester 
with  Safety  Valve. 


HYDROGEN. 


607 


There  are  many  other  modes  of  decomposing  water.  If  steam  is  passed 
over  red  hot  iron  borings,  the  metal  unites*with  the  oxygen,  and  the  hydrogen 
may  be  collected  in  the  ordinary  manner. 

When  the  electric  spark  from  a  coil  is  passed  through  steam,  the  latter  is 
decomposed  into  the  two  gases. 

A  small  pellet  of  sodium,  wrapped  in  blotting-paper  and  thrust  under  a  jar 
full  of  water  standing  on  the  pneumatic  trough,  immediately  liberates  hydrogen 
gas,  the  metal  taking  the  oxygen,  and  forming  with  the  water  sodium  hydrate, 
H  NaO,  which  is  quickly  dissolved.  A  very  small  piece  should  be  used,  as  the 
decomposition  occurs  with  explosive  violence. 

The  common  method  of  preparing  hydrogen  is  by  acting  on  zinc  with  dilute 
sulphuric  acid.  The  probable  metallic  character  of  the  hydrogen  is  well  illus¬ 
trated,  because  it  is  displaced  by  the  zinc,  sulphate  of  zinc  is  formed,  and  the 
hydrogen  escapes  in  the  gaseous  state.  The  change  which  occurs  is  explained 
in  the  following  simple  equation: 

H2SOt+Zn  =  ZnSO.+  H2 

Hydrogen  when  absolutely  pure  is  free  from  colour,  taste,  or  smell.  It  is 
the  lightest  of  all  known  substances,  being  about  fourteen  times  lighter  than 
atmospheric  air,  and  sixteen  times  lighter  than  oxygen  gas. 

A  hundred  cubic  inches  at  6o°  F.  and  30  in.  bar.  weigh  2T4  grains;  conse¬ 
quently  the  name  of  balloon  is  almost  synonymous  with  that  of  hydrogen, 
and  soap-bubbles  inflated  with  this  gas  rise  with  great  rapidity. 

Hydrogen  is  combustible  and  was  called  by  Cavendish  “inflammable  air.” 
A  burning  taper  is  extinguished  when  introduced  into  this  gas  ;  hence  oxygen 
was  called  a  “supporter,”  and  hydrogen  a  “non-supporter,”  of  combustion. 
But  this  expression  only  applies  to  the  test  of  a  lighted  taper,  as  a  jet  of  oxygen 
may  be  burnt  in  an  atmosphere  of  hydrogen,  just  as  the  latter  will  burn  in 
one  of  oxygen. 

This  element  when  inhaled  causes  the  voice  to  become  squeaky.  It  is  not 
poisonous,  though,  of  course,  it  must  be  remembered  that,  if  taken  into  the 
lungs,  it  displaces  so  much  air,  and  would  certainly  cause  insensibility  if 
inhaled  in  too  large  a  quantity. 

Synthesis  of  the  Elements  forming  Water.— When  two  volumes 
of  hydrogen  are  mixed  with  five  of  atmospheric  air  in  a 
long,  stout  glass  tube  provided  with  two  platinum  wires, 
standing  over  mercury,  called  an  “  eudiometer,”  and  the 
electric  spark  passed  between  the  platinum  wires,  a  flash 
of  light  takes  place,  and  expansion  occurs ;  therefore  a 
sufficient  height  of  mercury  must  always  be  left  in  the 
tube  :  steam  is  formed,  which  condenses  on  the  sides  of 
the  tube,  and  the  bulk  is  found  to  be  reduced  to  four 
measures,  viz.,  the  residual  nitrogen  left  after  one  mea¬ 
sure  of  oxygen  has  united  with  two  of  hydrogen. 

The  experiment  may  be  varied  by  mixing  two  vo¬ 
lumes  of  hydrogen  with  one  of  oxygen;  the  mixed  gases 
are  then  allowed  to  pass  into  a  very  strong  vessel  from 
which  the  air  has  been  carefully  removed,  and  when  full  in  which  Platinum 
the  stopcock  is  turned  off,  and  the  electric  spark  sent  Wires  are  inserted , 
through  the  mixed  gases:  light  is  seen,  but  little  or  no  with  Support  to  screw 
sound  is  heard;  and  this  experiment  may  be  repeated  on  the  side  of  a  Mer - 
over  and  over  again,  until  the  moisture  trickles  down  in  curial  Trough. 


f 


Fig.  480. — A  tube 


6o8 


CHEMISTR  Y. 


drops  of  water.  The  instrument  was  first  used  by  the  celebrated  Cavendish, 
and  is  always  called,  after  his  name,  the  Cavendish  bottle. 

A  jet  of  hydrogen  gas  burnt  under  a  gas-jar  containing 
common  air  soon  lines  the  interior  with  moisture, 
j  Dry  hydrogen  gas  passed  through  a  heated  glass  bulb 

1  containing  cupric  oxide,  CuO — the  black  oxide  of  cop¬ 

per — deprives  the  latter  of  oxygen.  Water  is  formed, 
and  the  equation  worked  out  by  comparing  the  loss 
of  weight  of  the  oxide  of  copper  with  the  condensed 
water  collected  affords  a  very  instructive  class  experi¬ 
ment. 

The  combustion  of  hydrogen  and  oxygen  for  the  pro¬ 
duction  of  the  lime  light  has  already  been  alluded  to 
in  the  article  on  Light. 

The  combination  of  the  two  gases  is  induced  by  the 
presence  of  finely-divided  platinum,  which  glow's  and 
becomes  red  hot  when  a  jet  of  hydrogen  is  directed  upon 
it.  Little  balls  made  of  pipeclay  and  spongy  platinum 
are  used  to  effect  the  combination  of  oxygen  and  hy¬ 
drogen.  In  certain  cases  where  the  analysis  of  a  mix¬ 
ture  of  gases  is  made,  it  is  usual  to  heat  the  ball  before 
inserting  it  into  the  mixed  gases,  standing  in  a  tube  over 
mercury  in  the  mercurial  trough,  of  which  several  con¬ 
venient  forms  are  shown  in  the  next  cuts  (Fig.  482). 
These  troughs,  as  their  name  implies,  are  filled  with 
mercury  instead  of  water,  because  many  gases  are  soluble  in  the  latter. 


Fig.  481. — The 
Cavendish  Bottle , 

Made  of  very  thick  glass, 
with  platinum  wires  in¬ 
serted  in  the  stopper, 
which  is  hela  down  by 
a  brass  framework. 


There  is  another  compound  of  oxygen  and  hydrogen,  called  dioxide  or  per¬ 
oxide  of  hydrogen,  or  hydric  peroxide,  H202.  It  acts  as  a  powerful  bleaching 
agent,  and  very  quickly  changes  into  oxygen  and  water;  hence  it  is  called 
oxygenated  water. 

This  brief  description  of  the  three  permanent  gases,  oxygen,  hydrogen,  and 
nitrogen,  will  hardly  be  complete  without  alluding  to  the  five  chemical  com¬ 
pounds  of  nitrogen  and  oxygen. 


COMPOUNDS  OF  NITROGEN  WITH  OXYGEN  Cog 


1.  Nitrous  oxide,  or  laughing  gas,  symbol  N20;  made  by  heating  dry  ammo¬ 
nium  nitrate  in  a  retort ;  the  salt  decomposes  into  this  gas  and  water. 

NH,NO,  ==  N20+2H20. 

Ammoniu  n  nitrate.  Nitrous  oxide  and  water. 

2.  Nitric  oxide,  NO;  a  colourless  gas,  prepared  by  heating  copper  wire  in 
dilute  nitric  acid.  In  contact  with  oxygen  it  forms  red  fumes  soluble  in  water. 

3.  Nitric  trioxide,  or  nitrous  anhydride,  N.O3. 

4.  Nitric  tetroxide,  or  nitric  peroxide,  NOa.  Constitutes  the  chief  portion 
f  the  red  fumes  produced  when  nitric  oxide  is  mixed  with  oxygen  gas. 

5.  Nitric  anhydride,  N2Os,  prepared  by  passing  dry  chlorine  gas  over  chloride 
of  silver.  It  is  nitric  acid  anhydrous,  or  free  from  water,  anti  is  a  white  crys¬ 
talline  substance,  called  also  nitric  pentoxide. 

Nitric  acid,  the  monohydrate  .HNOj,  of  which  100  parts  contain 

N205  . 8572 

HzO . 14-28 


ioooo 

is  one  of  the  most  important  acids,  or  rather — to  speak  according  to  modern 
theory,  “salts  of  hydrogen” — with  which  we  are  acquainted. 

It  can  be  made  by  acting  on  nitre  with  strong  sulphuric  acid,  and  is  easily 
produced  by  distilling  in  a  glass  retort  a  mixture  of  the  two  substances. 

This  acid  is  a  most  powerful  oxidizing  agent:  it  will  set  fire  to  finely-powdered 
charcoal,  or  even  straw,  and  is  used  in  nearly  every  case  where  a  metal  has 
to  be  oxidized  and  dissolved.  It  was  formerly  called  “aqua  fortis,”  and  is 
used  extensively  in  the  manufacture  of  gun  cotton  and  in  many  other  chemical 
processes. 

N  itric  acid,  or  hydric  nitrate,  is  prepared  by  heating  in  a  retort  equal  weights 
of  nitre  and  oil  of  vitriol :  red  fumes  are  produced,  and  a  very  strong  acid 
distils  over—  H  NO*—  having  a  specific  gravity  of  1-517.  On  the  large  scale 
(when,  for  instance,  it  is  required  in  the  manufacture  of  gun  cotton)  large  iron 
retorts  lined  with  fire-clay  are  employed.  Nitrate  of  soda  is  used  because  it 
is  cheaper  than  nitre,  and  yields  nine  per  cent,  more  acid. 

The  following  equation  explains  the  decomposition  : 

Nitrate  of  smla,  Oil  of  vitriol.  Nitric  acid,  Hydrosodic 

Sodic  nitrate.  Dihydric  sulphate.  Hvdric  nitrate.  sulphate. 

NaNO,  +  HsS04  +  HNOs  +  NaHSO* 

The  writer  has  paid  several  visits  to  the  admirably  arranged  gun  cotton 
factories  of  Messrs.  Thomas  Prentice  and  Co.,  Stowmarket,  and  is  enabled  to 
vouch  for  the  truth  of  the  follow  ing  particulars,  so  ably  described  bv  “  En¬ 
gineering,”  November,  1857. 

“  The  places  at  which  the  manufacture  of  gun  cotton  has  ever  been  exten¬ 
sively  carried  on  are  but  few  in  number.  Soon  after  Schonbein,  in  1846,  made 
known  the  manner  in  which  the  material  could  be  prepared,  its  manufacture 
was  taken  up  to  some  extent  at  the  powder-mills  of  Bouchet,  near  Paris,  and 
in  this  country  Messrs.  Hall  also  commenced  making  it  at  their  works  at 
Faversham.  At  the  latter  works,  however,  a  disastrous  explosion  occurred, 
which  was  attributed  by  the  jury  to  the  spontaneous  combustion  of  the  cotton; 
a^d  after  this  the  manufacture  was  discontinued,  a  large  quantity  of  gun  cotton 
which  happened  to  be  on  stock  at  the  time  being  buried.  This  was  in  July, 

3 


6io 


CHEMISTR  Y 


1847.  In  France  also  the  manufacture  was  abandoned  after  a  time,  the  French 
Commission  being  unable  to  produce  a  material  possessing  the  require! 
qualities;  and  in  Prussia,  where  the  manufacture  of  gun  cotton  had  also  been 
taken  up  by  the  Government,  the  experiments,  which  were  carried  on  for  eight 
years,  were  brought  to  an  end  by  the  blowing  up  of  .the  factory.  More  recently, 
the  process  of  manufacture  advocated  by  Baron  von  Lenk  was  taken  up 
strongly  in  Austria,  where  a  special  factory  was  erected  at  Hirtenberg;  but 
Baron  von  Lenk’s  system  did  not  prove  perfectly  successful,  and  in  1865  the 
Austrian  Government  gave  orders  that  the  ordnance  which  had  been  specially 
constructed  to  be  used  with  gun  cotton  should  be  altered  so  that  they  could 
be  used  with  powder,  the  use  of  gun  cotton  being  from  that  date  practically 
abandoned  in  the  Austrian  service. 

“  N otwithstanding  these  failures,  however,  the  advocates  of  gun  cotton— and 
notably  Professor  Abel,  the  director  of  the  chemical  department  of  our  War 
Office — continued  their  researches ;  and,  thanks  to  these,  the  manufacture  of 
gun  cotton  has  been  very  greatly  improved,  and  is  now  established  on  a  better 
basis  than  ever.  At  the  present  time  gun  cotton  is  being  manufactured  in  this 
country  at  two  places,  the  one  being  the  Government  powder-works  at  Walt¬ 
ham  Abbey,  and  the  other  the  extensive  works  of  Messrs.  Thomas  Prentice 
and  Sons,  of  Stowmarket,  a  firm  who,  by  their  extensive  experiments  on  a 
manufacturing  scale,  have  done  much  to  bring  the  gun  cotton  manufacture  to 
its  present  state.  The  two  chief  features  in  the  processes  now  followed,  as 
distinguished  from  those  carried  on  by  Baron  von  Lenk,  are  the  pul  fing  of 
the  cotton  after  its  conversion,  and  the  admixture  of  this  pulp,  in  some  cases, 
with  a  certain  proportion  of  plain  cotton  pulp,  for  the  purpose  of  retarding  the 
charges,  or  diminishing  the  rapidity  of  their  combustion.  The  various  pro¬ 
cesses  followed  during  the  manufacture  of  the  cotton  will,  however,  be  bost 
explained  by  a  description  of  Messrs.  Prentice’s  works  at  Stowmarket,  which 
we  now  propose  to  give. 

“  The  gun  cotton  factory  of  Messrs.  Thomas  Prentice  and  Sons  is  situated 
on  the  outskirts  of  the  town  of  Stowmarket,  by  the  side  of  a  stream  which 
furnishes  a  supply  of  water  for  washing  purposes,  and  also  drives  a  water¬ 
wheel  b/  which  the  pulping  machinery  is  worked.  The  factory  consists  of  two 
distinct  divisions,  one  devoted  to  the  manufacture  of  mining  charges,  and  the 
other  to  the  production  of  cartridges  for  small  arms,  there  being  besides  some 
shops  common  to  both  departments,  where  the  conversion  of  the  cotton  and 
its  formation  into  pulp  are  carried  on. 

“  The  raw  material  is  received  principally  in  the  form  of  “waste.”  Formerly 
gun  cotton  was  made  exclusively  from  cotton  wool;  but  Baron  von  Lenk  in¬ 
troduced  the  use  of  cotton  in  the  form  of  hanks  or  skeins,  it  being  urged  that 
these  were  more  readily  penetrated  by  the  acids  than  the  wool,  which  tended 
to  cake  into  a  mass  when  immersed.  Now,  however,  it  is  found  that  cotton 
in  almost  any  form  answers  equally  well  for  the  manufacture  of  gun  cotton, 
the  process  now  followed  ensuring  thorough  conversion  in  all  cases.  The  first 
thing  done  is  to  thoroughly  cleanse  the  raw  material.  This  is  effected  by  boiling 
it  in  an  alkaline  solution,  then  drying  it  in  a  centrifugal  machine,  and  then  again 
boiling  it  in  clean  water.  After  the  second  boiling  it  is  again  partially  dried 
in  a  centrifugal  machine,  and  any  remaining  moisture  is  thoroughly  removed, 
partly  by  exposing  the  cotton  to  the  atmosphere,  and  partly  by  placing  it  on 
shelves  in  a  drying-chamber  heated  artificially  to  about  120°.  The  drying  of 
the  cotton  has  to  be  very  thoroughly  effected,  as  any  moisture  which  might 


GUN  COTTON. 


6/  r 


remain  in  it  would,  by  combining  with  the  acids  used  for  conversion,  generate 
heat  and  set  up  a  destructive  action.  The  centrifugal  drying  machines,  which 
are  extensively  used  at  various  stages  of  the  manufacture,  are  of  ordinary  con¬ 
struction,  each  consisting  of  a  cylinder  with  wire  gauze  sides,  caused  to  revolve 
horizontally  at  the  rate  of  from  500  to  800  revolutions  per  minute.  A  number 
of  the  machines  at  Stowmarket  are  worked  from  shafting  driven  by  a  hori¬ 
zontal  engine,  and  others  are  driven  each  by  a  special  engine  placed  close  to 
the  machine,  these  engines  having  their  crank-shafts  arranged  vertically,  and 
the  fly-wheel  of  each  engine  being  connected  directly  by  a  belt  to  the  pulley 
on  the  spindle  of  the  corresponding  drying  machine. 

“The  cotton,  after  having  been  thoroughly  washed  and  dried,  is  weighed 
out  in  the  drying-room  into  charges  of  1  lb.,  each  charge  being  placed  in  a 
wooden  box  in  which  it  is  passed  into  the  converting-room.  There  each 
charge  is  placed  separately  in  a  bath  containing  the  mixed  acids,  the  mixture 
in  which  the  cotton  is  submerged  consisting  of  three  parts,  by  weight,  of  sul¬ 
phuric  acid  and  one  part  of  nitric  acid,  this  mixture  being  allowed  to  cool 
down — a  process  which  occupies  two  or  three  days — before  the  cotton  is  placed 
in  it.  After  immersion,  the  charges  of  cotton  are  strained  until  each  contains 
only  about  ten  times  its  weight  of  acids,  and  each  charge  is  then  placed  in  an 
earthenware  jar  and  covered  down.  In  order  to  prevent  any  heating  of  the 
cotton  from  taking  place,  the  jars  containing  it  are  arranged  in  a  kind  of 
shallow  trough  through  which  a  current  of  cold  water  is  kept  constantly  flow¬ 
ing.  The  building  in  which  the  conversion  of  the  cotton  is  effected  is  ventilated 
by  a  shaft  in  which  an  artificial  current  is  maintained  ;  but  the  ventilation  can 
scarcely  be  called  perfect,  and  it  is  doubtful  whether  the  fumes  arising  from 
the  acids  could  not  be  more  completely  removed  by  a  series  of  flues  connected 
with  the  shaft,  and  arranged  so  as  to  draw  off  the  air  from  the  floor  of  the 
room  close  to  the  bath  in  which  the  acids  are  contained.  This  system  of  ven¬ 
tilation  has  been  advocated  by  General  Morin,  and  has,  we  believe,  been  found 
very  effective  in  similar  cases. 

“  The  action  which  takes  place  when  the  cotton  is  immersed  in  the  mixed 
acids  is  as  follows :  Cotton,  when  pure,  is  one  form  of  cellulose,  and  is  an 
organic  compound  consisting  of  thirty-six  equivalents  of  carbon  and  thirty 
equivalents  of  hydrogen — both  combustible  or  oxidizable  elements — together 
with  thirty  equivalents  of  oxygen,  its  composition  being  thus  expressed  by  the 
chemical  formula,  C^H^Oso.  Nitric  acid,  on  the  other  hand,  is  a  powerful 
oxidizer,  and,  if  added  to  cotton  and  its  action  assisted  by  heat,  it  will  rapidly 
oxidize  not  only  the  hydrogen,  but  a  portion  of  the  carbon  which  the  cotton 
contains.  In  the  manufacture  of  gun  cotton,  however,  instead  of  the  action 
of  the  acid  being  assisted  by  heat,  care  is  taken  to  abstract  any  heat  as  soon 
as  it  may  arise,  and  the  action  of  the  acid  is  thus  moderated,  only  a  certain 
proportion  of  the  hydrogen  being  oxidized,  and  the  carbon  being  unaffected. 
The  nitric  acid  is,  as  we  have  said,  mixed  with  three  times  its  own  weight  of 
sulphuric  acid,  and  the  purpose  fulfilled  by  the  latter  is  that  of  intensifying  the 
action  of  the  nitric  acid  by  absorbing  the  w'ater  with  which  even  the  strongest 
nitric  acid  is  diluted,  and  also  the  water  set  free  by  the  action  of  the  nitric 
acid  upon  the  cotton.  The  hydrogen  removed  from  the  cotton  is  replaced  by 
an  equivalent  quantity  of  nitric  acid,  which  has  lost  a  portion  of  oxygen,  and 
has  thus  become  peroxide  of  nitrogen,  and  it  is  the  introduction  of  this  com¬ 
ponent  which  gives  the  gun  cotton  its  explosive  qualities.  The  peroxide  of 
nitrogen  is  a  powerful  oxidizing  agent — although  not  so  powerful  a  one  as  the 

39 — 2 


6l2 


CHEMISTR  Y. 


nitric  acid — and  it  only  requires  the  aid  of  heat  to  enable  it  to  oxidize  the 
carbon  and  the  remainder  of  the  hydrogen  contained  in  the  cotton,  and  con¬ 
vert  them  into  gases  with  explosive  rapidity.  The  heat  necessary  for  setting 
ap  this  action  is  supplied  when  the  cotton  is  ignited,  and  the  action  is  aided 
by  the  oxygen  contained  in  the  cotton  itself.  The  proportion  of  the  hydrogen 
originally  oxidized  by  the  action  of  the  mixed  acids  depends  upon  the  strength 
of  those  acids,  and  upon  the  purity  of  the  cotton  subjected  to  them.  Accord¬ 
ing  to  Mr.  Hadow,  of  King’s  College,  who  has  devoted  much  time  to  the  in¬ 
vestigation  of  the  chemical  changes  which  go  on  during  the  process  of  conver¬ 
sion,  there  are  four  distinct  varieties  of  gun  cotton,  each  containing  a  different 
proportion  of  peroxide  of  nitrogen.  When  pure  cotton  and  the  most  concen¬ 
trated  nitric  and  sulphuric  acids — of  the  specific  gravities  1*5  and  1  84  respec¬ 
tively — are  used,  he  states  that  nine  equivalents  of  hydrogen  contained  in  the 
cotton  are  replaced  by  nine  equivalents  of  peroxide  of  nitrogen,  its  composi¬ 
tion  being  thus  expressed  by  the  formula,  Cjr,H2i9(N04)03o.  This  Mr.  Hadow 
gives  as  the  composition  of  Baron  von  Lenk’s  gun  cotton ;  in  the  three  other 
varieties  he  states  that  the  numbers  of  equivalents  of  hydrogen  replaced  by 
peroxide  of  nitrogen  are  eight,  seven,  and  six  respectively.  By  the  process  of 
conversion  the  cotton  is  not  altered  in  appearance,  but  it  is  materially  in¬ 
creased  in  weight  in  the  proportion  of  about  7  to  4. 

“  At  Stowmarket,  the  cotton,  after  being  exposed  to  the  action  of  the  acids 
for  forty-eight  hours  in  order  to  ensure  its  thorough  conversion,  is  removed 
from  the  jars  and  placed  in  a  centrifugal  drying  machine,  which  removes  the 
greater  proportion  of  the  free  acids.  On  its  removal  from  the  centrifugal  dry¬ 
ing  machine  it  is  plunged  suddenly  into  a  strong  fall  of  water  received  by  a 
tank,  in  which  the  gun  cotton  placed  in  the  fall  is  allowed  to  remain  for  a 
short  time.  The  object  ol  placing  the  gun  cotton  in  the  fall  of  water,  or 
‘drench-bath,’  as  it  is  called,  is  to  ensure  the  sudden  and  complete  submersion 
of  the  material,  and  thus  avoid  the  heating  and  decomposition  of  the  cotton 
which  would  take  place  at  the  surface  of  the  water  if  the  cotton  were  immersed 
gradually.  On  its  removal  from  the  drench-bath,  the  gun  cotton  is  again 
dried  in  a  centrifugal  machine,  and  then  placed  in  a  bath  through  which  a 
current  of  water  constantly  flows  for  forty-eight  hours.  After  this  it  is  again 
dried,  and  then  placed  in  a  second  bath  for  a  similar  period,  these  alternate 
washings  and  dryings  being  repeated  until  the  gun  cotton  has  passed  through 
eight  baths  successively,  remaining  forty-eight  hours  in  each. 

“  After  having  been  removed  from  the  eighth  bath  and  dried,  the  cotton  is 
ready  for  pulping,  a  process  which  is  in  itself  a  washing  of  the  most  effective 
kind. 

“The  pulping  machinery  at  Messrs.  Prentice’s  works  is  driven  by  a  water¬ 
wheel.  The  pulping  machines,  of  which  there  are  two,  are  similar  to  those 
employed  in  paper-mills. 

“  For  making  the  mining  charges,  the  pulp  is  first  placed  in  a  centrifugal 
machine,  and  as  much  water  expelled  as  is  possible  by  such  means.  When 
removed  from  the  machine,  the  pulp  is  not  completely  dried;  but  the  propor¬ 
tionate  quantity  of  water  which  it  contains  is  known,  so  that  it  can  be  weighed 
up  into  charges  as  accurately  as  if  it  were  dried  perfectly.  The  weighing  of 
the  dried  pulp  is  effected  by  a  number  of  girls,  the  weighing  scales  being  situ¬ 
ated  in  a  light  wooden  building.  Each  charge,  on  being  weighed,  is  placed 
in  a  small  tin  vessel,  in  which  it  is  conveyed  to  the  pressing-house,  where  the 
charges  are  again  moistened  with  water.  The  sole  object  of  temporarily  dry- 


GUN  COTTON. 


613 


ing  the  pulp  is,  in  fact,  to  enable  it  to  be  accurately  weighed  out  into  charges, 
and  after  this  weighing  has  been  effected  it  is  kept  moist  in  all  stages  of  its 
manufacture  until  it  is  subjected  to  the  final  drying  process. 

“  The  charges  are  first  hand-pressed,  and  are  then  subjected  to  a  more 
severe  pressure  by  the  aid  of  machinery.  The  hand-pressing  is  effected  by 
boys,  as  follows :  Each  charge,  after  being  moistened  with  water,  is  transferred 
from  the  tin  cup  containing  it  into  a  cylindrical  mould  or  tube,  the  internal 
diameter  of  which  is  equal  to  the  external  diameter  of  the  intended  charge. 
At  first  these  tubes  were  made  solid  at  the  lower  end ;  but  it  was  found  that 
the  gun  cotton  or  pulp  charge,  when  introduced  into  them,  formed  a  kind  of 
piston,  below  which  the  air  contained  in  the  tube  became  compressed,  and 
under  these  circumstances  it  was  found  impossible  to  get  the  charges  fairly 
home  to  the  bottom  of  the  tubes.  This  difficulty  has  been  got  over  in  a  very 
ingenious  manner.  Instead  of  the  tubes  being  made  completely  closed  at  the 
lower  end,  the  latter  is  perforated,  and  the  solid  bottom  on  which  the  charge 
rests  is  formed  by  a  piston,  with  which  each  tube  is  fitted.  Th-is  piston  is 
furnished  with  a  rod,  which  passes  up  through  the  centre  of  the  charge,  form¬ 
ing  a  hole  through  the  latter,  which  enables  the  charge  to  be  ignited  from  end 
to  end  by  the  flash  of  the  portion  first  lighted.  In  the  case  of  charges  the  dia¬ 
meter  of  which  exceeds  about  1^  in.,  the  pistons  of  the  moulds  are  furnished 
with  two  rods,  one  of  these  forming  the  central  hole,  and  the  other  a  hole 
nearer  the  circumference,  in  which  the  end  of  the  igniting  fuse  can  be  placed. 

”  To  return,  however,  to  the  process  of  pressing:  the  piston  being  first  placed 
in  the  mould  and  pushed  in  a  small  distance,  the  charge  is  rammed  in  on  the 
top  of  it,  and  then  on  the  piston  being  forced  down  to  the  bottom  of  the  mould 
by  the  aid  of  its  rod,  the  atmospheric  pressure  on  the  top  of  the  charge  causes 
it  to  be  carried  down  in  close  contact  with  the  piston.  A  hollow  plunger,  per¬ 
forated  at  the  bottom  and  sides,  is  next  placed  in  the  mould,  the  end  of  this 
plunger  having  a  hole  or  holes  in  it,  through  which  the  rod  or  rods  of  the 
piston  can  pass ;  and  the  whole  is  then  placed  under  a  hand-lever,  by  which 
the  plunger  is  forced  down  on  the  charge,  and  the  latter  compressed  to  some 
extent.  The  charges,  on  being  removed  from  the  moulds  above  described, 
are  next  subjected  to  a  more  severe  pressure  by  steam  power.  Two  machines 
are  used  for  this  purpose,  one  of  them,  which  is  used  for  the  larger  charges, 
being  a  specially  fitted  up  hydraulic  press,  and  the  other  somewhat  resembling 
a  slotting  machine  in  its  general  appearance.  "1  he  slide  of  this  latter  machine, 
however,  instead  of  carrying  a  cutting-tool,  is  fitted  with  three  plungers,  w  hich 
act  upon  each  charge  successively.  The  charge  to  be  pressed  is  placed  in  a 
cylindrical  mould,  carried  by  a  horizontal  circular  table  having  an  intermittent 
rotary  motion.  By  one  movement  of  this  table  the  mould  is  brought  under 
the  first  plunger  of  the  slide,  which  partially  compresses  the  charge,  and,  on 
the  return  stroke  of  this  plunger,  the  further  movement  of  the  table  brings  the 
charge  under  the  second  plunger,  which  on  making  its  next  stroke  completes 
the  compression.  A  third  movement  of  the  table  brings  the  mould  under  the 
third  plunger,  which  on  its  descent  forces  the  charge  out  of  the  mould,  the 
latter  having,  by  this  third  movement  of  the  table,  been  brought  over  a  hole 
through  which  the  false  bottom  of  the  mould  and  the  charge  can  pass.  A 
fourth  movement  of  the  table  brings  the  mould  into  a  position  where  it  can 
receive  a  fresh  charge.  The  moulds  and  plungers  are  formed  so  as  to  allow 
of  the  escape  of  the  water  expressed  from  the  charges,  and  the  revolving  table 
is  supplied  with  several  moulds,  so  that  the  piocesses  of  partial  compression, 


CHEMISTRY. 


6x4 


complete  compression,  and  the  expulsion  of  the  charges  are  carried  on  simul¬ 
taneously,  there  being  always  three  charges  under  operation. 

“  For  effecting  the  compression  of  the  larger  charges  an  entirely  different 
apparatus  is  employed.  This  consists  of  a  horizontal  hydraulic  cylinder,  the 
main  plunger  of  which  is  furnished  with  a  head  carrying  a  number  of  small 
plungers  for  compressing  the  charges,  these  plungers  being  arranged  in  par¬ 
allel  rows  one  above  the  other.  Facing  the  plunger  is  the  fixed  head  of  the 
press  upon  which  the  pressure  is  received,  and  between  this  and  the  press 
cylinder  is  placed  a  block  of  zinc,  perforated  to  receive  the  charges,  and  also 
another  block,  the  use  of  which  will  be  explained  presently.  Both  these  blocks 
are  capable  of  being  slid  on  one  side,  the  lateral  movement  enabling  the  un¬ 
compressed  charges  to  be  placed  in  the  zinc  block.  The  second  block,  which 
is  of  iron,  has,  we  should  mention,  a  number  of  pieces  of  zinc  let  into  it  at  the 
points  at  which  the  charges  directly  bear  upon  it.  The  method  of  using  this 
apparatus  is  as  follows  :  The  charges  to  be  compressed  having  been  placed 
in  the  holes  in  the  zinc  block,  the  latter  is  brought  into  its  proper  position 
in  front  of  the  plungers,  with  the  second  block  behind  it,  and  secured  by  a 
simple  contrivance  provided  for  the  purpose.  Water  is  then  forced  into  the 
press  by  pumps  worked  by  a  small  steam  engine  close  at  hand,  when  the 
plungers  enter  the  holes  containing  the  charges,  and  compress  the  latter  to 
the  required  extent.  The  water  pressure  is  next  removed,  and  the  plunger 
allowed  to  recede  to  a  sufficient  extent  to  leave  the  second  block  loose.  This 
block  is  then  run  on  one  side,  and  a  box  furnished  with  as  many  shelves  as 
there  are  rows  of  charges  being  substituted  for  it,  the  water  pressure  is  again 
put  on,  and  the  plungers,  advancing,  force  the  charges  out  of  the  holes  in  the 
zinc  block  into  the  box  placed  to  receive  them.  The  press  is,  of  course,  fur¬ 
nished  with  a  number  of  zinc  blocks  and  sets  of  plungers,  correspond. ng  to 
charges  of  different  diameters,  and  the  arrangement  is  found  to  be  a  very 
efficient  one. 

“The  next  process  undergone  by  the  charges  after  pressing  is  that  of  being 
covered  with  a  peculiar  kind  of  paper  termed  ‘  artificial  vellum.’  This  artificial 
vellum,  which  is  manufactured  by  Messrs.  Prentice  on  their  own  works,  is 
made  by  laying  sheets  of  blotting-paper  for  a  few  seconds  on  the  surface  of 
strong  sulphuric  acid  contained  in  a  suitable  bath.  The  paper,  after  being 
subjected  to  the  action  of  the  acid,  is  immediately  washed  by  plunging  into 
troughs  containing  water,  and  on  its  removal  from  these  troughs  it  is  ready 
for  use.  The  process  of  manufacturing  this  material  is  a  very  interesting  one 
to  witness,  the  artificial  vellum  being  a  tough  semi-tran:parent  substance,  so 
entirely  different  to  the  blotting-paper  from  which  it  is  produced,  that  it  is 
almost  difficult  to  believe  that  the  transformation  could  be  effected  by  such 
simple  means.  The  artificial  vellum  is  cut  into  strips,  rolled  around  the  charges, 
and  secured  by  paste,  the  operation  of  covering  the  charges  being  performed 
by  girls. 

“After  being  covered  the  charges  are  ready  for  the  final  process  of  drying; 
and  this  drying  is  effected  by  the  aid  of  steam,  the  drying-stove  being  situated 
at  some  little  distance  from  the  sheds  in  which  the  other  processes  are  carried 
on.  The  stove  consists  of  a  small  brick  erection  enclosing  the  steam-pipes, 
the  top  of  the  brickwork  being  fitted  with  a  number  of  vessels  in  which  the 
charges  to  be  dried  are  placed.  The  vessels  are  separated  from  each  other  by 
division  wails  carried  up  between  them,  so  that,  in  the  event  of  the  contents 
of  one  vessel  becoming  ignited,  the  flame  will  not  be  communicated  to  the 


GUN  COTTON. 


6l5 


Other  vessels,  and  they  are  protected  from  the  weather  by  light  hoods  placed 
over  them.  The  charges  are  dried  at  a  temperature  of  about  140°,  and  efficient 
means  are  provided  for  ensuring  that  the  temperature  shall  never  rise  above  a 
perfectly  safe  limit. 

•‘We  have  seen  that,  in  the  case  of  the  mining  charges,  the  pulp  is,  during 
the  process  of  manufacture,  subjected  to  very  severe  compression,  and  by  this 
means  a  very  great  quantity  of  explosive  matter  is  obtained  in  a  small  bulk. 
A  mining  charge,  in  fact,  manufactured  by  the  processes  now  followed  at  Stow- 
market  possesses  an  amount  of  explosive  power  six  times  as  great  as  that  of 
a  similar  bulk  of  gunpowder;  and  this  concentration — if  we  may  term  it  so — 
of  the  explosive  material  is  in  many  instances  of  great  value.  Thus,  when 
hard  materials  have  to  be  blasted  by  charges  contained  in  holes  bored  only  to 
a  moderate  depth,  a  gun  cotton  charge,  occupying  only  one-sixth  the  length 
of  hole  that  would  be  taken  up  by  a  gunpowder  charge  of  equal  power,  allows 
of  a  greater  length  of  tamping  being  employed,  and  also  concentrates  the  ex¬ 
plosive  action  at  greater  distance  from  the  working  face.  There  is  also  now 
abundant  evidence  that  gun  cotton  is  in  other  respects  a  more  effective  ex¬ 
plosive  for  mining  and  quarrying  purposes  than  gunpowder.  Thus,  in  break¬ 
ing  up  large  boulders  by  means  of  a  charge  inserted  in  a  vertical  hole  bored 
from  the  top  down  to  near  the  centre  of  the  boulder,  if  a  gunpowder  charge  is 
employed,  its  tendency  is,  if  the  block  is  of  large  size,  to  blow  out  a  conical 
mass  from  the  upper  part  of  the  boulder,  the  apex  of  this  inverted  cone  being 
situated  at  the  point  where  the  charge  is  placed.  With  gun  cotton,  however, 
the  case  is  different,  it  being  found  that  it  exerts  a  powerful  splitting  action 
below  as  well  as  above  the  point  where  the  charge  was  situated.  This  effect 
appears  to  be  due  to  the  extremely  rapid  action  of  the  gun  cotton ;  but,  what¬ 
ever  may  be  the  cause,  it  is  an  effect  which  is  found  to  occur  in  practice,  and 
one  which  makes  gun  cotton  particularly  valuable  for  quarrying  purposes.” 

There  are  some  very  remarkable  circumstances  connected  with  the  ignition 
of  gun  cotton  which  show  that  almost  any  rate  of  combustion  may  be  obtained 
by  using  a  variety  of  heat-giving  agents. 

Thus,  if  a  length  of  gun  cotton  yarn  is  fired  with  the  incandescent  charcoal 
or  glowing  spark  at  the  end  of  a  piece  of  string  after  the  flame  is  blown  out, 
it  causes  the  cotton  to  burn  slowly  like  a  squib.  If  the  flame  of  the  burning 
string  be  used,  or  any  other  flame,  the  gun  cotton  puffs  off  with  the  usual 
rapidity  of  combustion. 

A  still  more  rapid  combustion  is  secured  by  exploding  gun  cotton  with  ful¬ 
minating  mercury,  when  the  destructive  and  rending  power  is  tremendous. 
The  writer  witnessed  some  experiments  kindly  conducted  by  Messrs.  Prentice 
at  Stowmarket.  Loose  gun  cotton  may  be  laid  by  the  side  of  a  wall  or  stout 
wooden  palisade,  and  if  fired  in  the  ordinary  way  with  flame,  little  or  no  efiect 
would  be  produced ;  but  when  the  fire  is  communicated  to  the  gun  cotton  by 
the  concussion  or  combustion  of  fulminating  mercury,  the  same  kind  of  almost 
electric  rapidity  of  combustion  is  conferred  on  the  gun  cotton,  which  explodes 
with  a  loud  noise,  and  will  then  blow  down  the  wall  or  wooden  fencing  with 
comparatively  moderate  charges. 

There  are,  therefore,  three  distinct  rates  of  combustion  belonging  to  gun 
cotton,  which  are  determined  by  the  nature  of  the  tire  used: 

1.  A  spark  of  incandescent  charcoal  causes  it  to  burn  slowly,  like  a  pyro 
technic  mixture. 

2.  With  flame  it  puffs  off  rapidly. 


6 1 6 


CHEMISTR  Y. 


3.  By  the  fire  and  percussive  power  of  fulminating  mercury  gun  cotton  ex¬ 
plodes  with  the  fearful  violence  belonging  to  trinitro-glycerine,  which  is  sup¬ 
posed  to  have  at  least  ten  times  more  explosive  force  than  gunpowder,  and  is 
so  dangerous  that  its  use  in  England  is  virtually  arrested  from  the  circum¬ 
stance  that  no  railway  or  ship  will  knowingly  carry  this  terrible  oil,  which  is 
prepared  from  glycerine  by  the  action  of  concentrated  nitric  acid. 

Glycerine — C,H80;, — acted  upon  by  strong  nitric  acid  is  converted  into  tri¬ 
nitro-glycerine,  in  which  three  atoms  of  typical  hydrogen  are  replaced  by  three 
of  nitric  peroxide,  C3H5,  3N02,  03,  affording  another  remarkable  instance  of 
the  fact  that  all  the  most  dangerous  explosive  bodies  contain  nitrogen. 

“The  Times”  of  28th  January,  1869,  gives  the  following  graphic  account 
of  the  effect  of  various  charges  of  gun  cotton,  fired  with  the  detonating  fuse, 
by  Messrs.  Thomas  Prentice  and  Co.,  at  Stowmarket.  After  many  details  of 
the  manufacture  of  the  gun  cotton,  the  article  concludes  as  follows : 

“  On  quitting  the  practice-ground,  the  party  set  off  to  walk  far  afield,  for 
though  small  charges  of  gun  cotton  may  be  fired  close  to  a  village,  it  is  other¬ 
wise  with  quantities  large  enough  to  blow  down  palisades  or  break  up  trunks 
of  trees.  As  the  first  experiment,  a  disc  of  gun  cotton,  weighing  about  1  lb. 
1  oz.,  was  placed  on  the  stump  of  a  tree  lately  cut  down,  and  ignited  by  an 
ordinary  piece  of  miner’s  fuse.  At  the  instant  of  ignition  it  was  enveloped  in 
flame,  and  sailed  merrily  about  for  the  two  or  three  seconds  required  for  its 
combustion.  The  gas  produced  lifted  it  up  and  caused  it  to  move.  Then 
about  half  the  quantity  was  placed  on  the  same  spot  and  ignited  by  a  small 
detonating  tube.  A  sharp,  sudden  report  was  heard,  and  the  stump  was  found 
on  inspection  to  be  partly  penetrated  just  where  the  charge  had  lain,  while 
the  twigs  of  the  hedge  close  by  suffered  severely.  On  seeking  for  a  new  illus¬ 
tration  a  large  tree-root  was  seen,  which  had  been  torn  out  of  the  ground,  and 
offered  among  its  gnarled  and  bossy  structure  a  favourable  position  to  deposit 
a  charge.  One  of  the  discs,  about  1  lb.  1  oz.,  was  accordingly  placed  at  the 
mouth  of  a  small  cave  that  seemed  inviting.  The  gun  cotton  was  not  buried 
in  the  mass,  but  only  laid,  as  it  were,  on  a  shelf  perlectly  open  to  the  air. 
The  gentlemen  present  retired  to  what  they  considered  a  safe  distance,  about 
fifty  yards.  There  seemed  to  be  some  doubt  about  the  effect.  Is  it  possible 
that  so  small  a  quantity  of  gun  cotton  could  rend  such  a  mass,  even  if  buried 
in  it  ?  Surely  not  when  it  is  only  laid  on  the  floor  of  an  opening.  The  moment 
of  explosion  is  anxiously  awaited.  A  man  lights  the  fuse  and  runs  for  his 
life.  There  is  a  little  smoke.  Is  the  cotton  burning  as  the  first  sample  did? 
Wait  a  little  yet.  The  tube  has  not  given  its  sharp,  cracking  sound.  One 
moment  more,  and  then  a  report  and  a  rush  through  the  air  of  masses  of 
wood — overhead,  right,  left,  in  front,  everywhere!  Soldiers  who  have  known 
what  it  is  to  be  under  shell  fire  ducked  to  dodge  a  big  lump  of  knotted  wood 
that  sprang  sixty-four  yards  from  its  parent  root,  just  clearing  the  heads  of 
the  party.  It  was  only  for  a  moment,  and  then  everybody  ran  to  see  what 
had  been  done.  The  whole  great  root  had  simply  been  shattered  to  pieces, 
and  grinning  countrymen  exclaimed,  ‘We  hope  you’ll  sarve  a  few  more  on 
’em  so  for  us.’  A  little  awed  by  what  they  had  seen,  the  visitors  toiled  and 
tumbled  over  a  heavy  ploughed  field  to  see  a  row  of  palisades  composed  of 
three  trunks,  some  of  them  18  in.  in  diameter,  and  all  sunk  4  ft.  into  the  ground. 
Since  the  last  explosion  everybody  had  been  a  little  more  careful  about  lighted 
cigars,  forgetting  that  a  cigar  or  even  a  match  would  ignite  the  gun  cotton  in 
quite  another  fashion.  A  long  tree-trunk  by  touching  the  foot  of  the  palisade, 


GUN  COTTON. 


617 


and  upon  this  5  lb.  of  gun  cotton  was  laid.  Wires  communicating  with  a 
magnetic  apparatus  were  affixed  to  a  detonating  tube,  which  was  placed  in 
contact  with  one  of  the  discs  of  gun  cotton.  ‘  But  surely  they  won’t  all  deto¬ 
nate,  for  only  their  circumferences  touch  at  one  point  ?’  Wait  and  see  ;  back 
over  the  heavy  furrows  a  good  1 50  yards,  no  one  being  anxious  to  stand  too 
near  this  time.  The  time  of  suspense  was  short,  and  then  the  explosion  was 
heard.  One  mass  of  wood  only  was  seen  to  plunge  away  from  the  palisade ; 
it  was  the  recumbent  trunk  upon  which  the  cotton  had  been  laid.  The  pali¬ 
sades  themselves  were  standing,  though  a  good  deal  damaged — no  practicable 
breach.  But  there  still  remained  a  long  space  of  palisading  yet  untouched, 
and  here,  instead  of  5  lbs.,  1 5  were  laid,  partly  built  on  each  other.  The  excite¬ 
ment  began  to  increase.  It  was  the  old  story  of  the  targets  and  the  guns,  and 
now  several  people  might  have  been  found  to  back  the  palisades.  Fuse  and 
wires  were  placed.  Everybody  retired  to  a  safe  distance.  Man’s  nervous 
organization  is  curiously  elaborated,  and  it  is  not  to  be  wondered  at  that  there 
were  several  exclamations  of,  ‘  Please  tell  us  just  when  you  are  going  to  fire.’ 
Some  persons  put  two  good  banks  between  them  and  the  expected  explosion, 
others  sought  the  grateful  shelter  of  a  ditch.  All  were  trying  to  combine  the 
maximum  of  view  with  the  minimum  of  danger.  At  last  came  the  sharp, 
powerful  crash,  so  unlike  the  dull  roar  of  gunpowder,  and  this  time  there  could 
be  no  mistake  about  the  effect.  Huge  logs  were  seen  performing  summer¬ 
saults  at  greater  or  less  distances  from  the  explosion,  while  smaller  pieces, 
some  about  a  couple  of  feet  square,  bounded  like  rabbits  over  the  field.  Men 
of  science,  officers,  country  gentlemen,  and  bumpkins  were  soon  spread  over 
the  ploughed  field,  each  striving  to  be  first  in  at  the  death.  On  reaching  the 
target  the  effect  appeared  to  have  been  tremendous.  In  some  places  a  tree- 
trunk  had  been  cut  in  half,  almost  as  with  a  rough  saw,  only  not  so  straight ; 
in  others  the  solid  wood  was  mangled,  so  that  it  could  be  pulled  to  pieces  by 
the  hand.  Three  logs  had  been  cut  down  or  smashed,  and  it  was  clear  that 
no  stockade  or  New  Zealand  pah  could  withstand  such  deadly  effects  for  an 
instant.  Exclamations  of  astonishment  showed  the  mental  impressions 
produced.  '‘EuperbeP  ‘Prodigious!’  ‘Extraordinary!’  ‘Magnificent!’ 
‘ Mais  e’es t  une  manure  de  faire  les  allumettes /’  And  all  this  had  been  done 
by  only  15  lbs.  of  the  cotton.  Three  times  the  quantity  made  up  into  a  cylinder 
could  be  carried  with  ease  by  a  man  at  a  run,  who  might  also  drag  the  ends 
of  the  two  wires  as  they  unwound  from  a  reel  kept  in  a  position  of  safety.  Is 
there  no  hint  here  for  the  colonists?  No  fire  need  be  seen,  for  there  is  no 
match  to  light.  Surely  plenty  of  volunteers  could  be  found  to  perform  such 
work  at  night,  and  so  restore  the  superiority  of  civilized  man  over  savages. 
It  had  been  contemplated  to  tie  a  ring  of  gun  cotton  round  a  living  tree,  and 
see  if  it  could  not  be  cut  down ;  but  there  was  not  time  enough.  1  he  experi¬ 
ments  were  over  for  the  day,  and  the  visitors  returned  to  London,  satisfied 
that  they  had  seen  a  most  marvellous  phenomenon,  and  one  which  is  only  a 
first  step  to  a  whole  array  of  novelties  in  the  arts  of  war  and  of  peace.  ’ 

When  the  tremendous  powers  of  modern  artillery  with  improved  gunpowder, 
and  all  the  terrible  refinements  in  the  management  of  gun  cotton,  are  consi¬ 
dered,  it  is  amusing  to  compare  the  latter  with  the  bows  and  arrows  used  only 
three  centuries  and  a  half  ago. 

Extract  from  the  “ Edinburgh  Con  rant” — “‘  I  have  seen  a  man  who  con¬ 
versed  with  a  man  who  fought  at  Flodden  Field,’  may  be  said  by  a  venerable 
octogenarian  gentleman,  to  whom  we  are  indebted  for  the  following  most  inte- 


CHEMISTR  Y 


6  [8 


resting  memorandum  : — The  writer  of  this,  when  an  infant,  saw  Peter  Garden, 
who  died  at  the  age  of  126.  When  twelve  years  old,  on  a  journey  to  London 
about  the  year  1670,  in  the  capacity  of  page  in  the  family  of  Garden  of  Troup, 
he  became  acquainted  with  the  venerable  Henry  Jenkins,  and  heard  him  give 
evidence  in  a  court  of  justice  at  York,  that  he  ‘perfectly  remembered  being 
employed, when  a  boy,  in  carrying  arrows  up  the  hill  at  the  battle  of  Flodden.’  ” 


It  was  fought  in  ...  . 

A  D. 

1513 

Add  Henry  Jenkins’s  age  . 

I69 

Les . . 

II 

— 

IS8 

Peter  Garden  . 

...  126 

Less  his  age  when  at  York 

12 

— 

114 

The  writer  of  this  in  1865  aged 

80 

186; 

Nitrogen  and  Hydrogen,  Ammonia,  H3N  =  i7. 

Many  thousand  years  ago  the  Egyptians  worshipped  a  god  “  Ammon,”  and 
it  is  said  that  as  this  compound  was  first  obtained  from  a  substance  found 
near  a  temple  devoted  to  the  worship  of  this  divinity,  situated  in  the  Oasis  of 
Ammonium  ( Siwah ),  in  the  Libyan  Desert,  celebrated  for  its  oracle  and  visited 
by  Alexander  the  Great, — as  the  compound  was  first  discovered  near  this 
temple,  it  was  called  Sal  Ammoniac. 

Quicklime  and  sal  ammoniac,  or  ammonia  hydrochlorate,  NH3HC1,  when 
mixed  and  gently  heated,  give  calcium  chloride,  ammonia,  and  water. 

CaO  +  2NH3HCl  =  CaCl2  +  2NH3+H20 

Calcic  oxide  and  ammonia  hydrochlorate  Calcium  chloride,  ammonia,  and  water. 

Ammonia  is  also  given  off  when  animal  matter  is  heated,  such  as  the  horns 
of  animals,  and  hence  it  was  called  “  hartshorn.”  The  first  ammonia  was 
doubtless  obtained  by  the  Arabs  near  the  temple  of  Jupiter  Ammon,  by  heating 
camels’  dung. 

Coal  is  the  great  source  of  ammonia,  and  this  is  not  surprising  when  it  is 
understood  that  it  contains  2  per  cent,  of  nitrogen. 

Guano  and  other  manures  are  applied  to  the  land  because  they  contain  free 
ammonia,  or  other  nitrogenous  matter,  ready  to  change  into  ammonia  and  to 
be  assimilated  by  plants. 

When  sal  ammoniac  and  quicklime  are  heated  in  a  flask  provided  with  a 
cork  and  tube,  the  gas  may  be  collected  over  mercury.  It  is  colourless,  but 
possesses  a  very  strong  odour,  affecting  greatly  the  olfactory  nerves,  and 
causing  a  flow  of  water  from  the  eyes,  and  hence  is  used  as  a  refreshing  stimu¬ 
lant,  and  is  slowly  evolved  from  mixtures  called  “  smelling  salts.”  Being 
lighter  than  air,  it  may  be  collected  by  holding  a  clean  dry  bottle  over  the 
mouth  of  a  flask  containing  the  mixture  of  lime  and  ammoniacal  salt ;  it  is 
better,  however,  to  pass  the  gas  first  through  a  bottle  containing  quicklime,  in 
order  to  remove  the  moisture.  Calcic  chloride  must  not  be  used,  as  it  absorbs 
ammonia  and  forms  a  definite  compound  with  that  body. 

The  specific  gravity  of  ammoniacal  gas  is  o-59o,  air  being  rooo;  and 
therefore  it  fills  an  inverted  bottle  by  displacement. 

Ammonia  cannot  be  collected  over  water,  as  it  is  so  very  soluble  in  that 
liquid.  At  the  freezing-point  water  takes  up  1,050  times  its  volume;  at  590, 
72 7  times  its  volume;  at  78°,  586  times  its  volume. 


AMMONIA. 


619 


Ry  conducting  the  ammoniacal  gas  into  a  series  of  Wolfe’s  bottles  provided 
with  safety  tubes,  the  ordinary  solution  of  ammonia  may  be  prepared. 


Fig.  483. — Retort  fitted  to  a  series  of  Wolfe's  Bottles , 

All  provided  with  safety  tubes. 


0 


VJ 


Whilst  the  ammonia  is  being  dissolved  the  water  becomes  very  hot,  and  if 
kept  at  6o°  by  the  application  of  a  current  of  cold  water,  it  will  dissolve  one- 
third  of  its  weight  of  the  gas,  and,  becoming  specifically  lighter,  is  then  found 
to  have  increased  in  bulk  by  one-half.  The  specific  gravity  of  the  strongest 
solution  of  ammonia  at  570  is  o-884,  water  being  rooo. 

Various  safety  tubes  are  made  when  gases  are  passed  into  water  or  other 
solutions :  one  of  the  most  elegant  is  that  shown  in  the 
annexed  cut.  The  object  of  a  safety  tube  is  to  prevent 
the  flask  being  crushed  or  the  liquid  returning  into  the 
materials  by  any  sudden  condensation  and  formation 
of  a  vacuum. 

Blotting-paper  coloured  yellow  with  turmeric,  called 
turmeric-paper,  is  instantly  changed  to  a  reddish  brown 
when  brought  in  contact  with  ammonia.  Other  alkalies 
affect  the  turmeric  in  the  same  manner;  but  the  effect 
of  ammonia'  is  soon  distinguished  from  others,  because, 
on  the  application  of  heat  to  the  paper,  the  ammonia 
is  driven  off,  and  the  yellow  colour  of  the  turmeric  is 
restored. 

At  a  pressure  of  seven  atmospheres,  at  6o°,  ammonia 
(the  gas)  condenses  into  a  liquid,  and  is  used  in  M. 

Carry’s  freezing  apparatus,  which  was  exhibited  on  a 
grand  scale  at  the  Great  French  Exhibition  of  1867. 

Ammonia  is  formed  by  the  union  of  three  volumes 
of  hydrogen  with  one  of  nitrogen,  and  its  symbol  is 
therefore  HSN. 

There  are  two  other  compounds  of  nitrogen  and  hy¬ 
drogen,  which  have  not  vet  been  obtained  in  an  isolated 
form,  viz., 

Amidogen,  H2N  =  i6. 

Ammonium,  H,N  =  i8. 


Fig.  484. 

A  Safety  Tube,  for 
Experiments  with 
Gases ,  &c. 


620 


CHEMISTRY. 


THE  HALOGENS 

(From  ak f,  sea-salt), 

CHLORINE,  IODINE,  BROMINE,  AND  FLUORINE. 
A  Group  of  Monads. 


CHLORINE. 

Symbol,  Cl.  Atomic  weight,  35 *5. 

The  fact  that  sea-salt  is  the  chief  source  of  Chlorine  is  sufficient  to  demon¬ 
strate  its  plentifulness;  and  its  presence  in  soils,  plants,  animals,  natural 
waters,  sea-water,  sea-salt,  and  rock-salt,  all  confirm  the  statement. 

This  gas,  discovered  by  Scheele  in  the  year  1774,  is  called  chlorine  from  the 
Greek  ^Awpocr,  green,  in  allusion  to  its  peculiar  yellowish-green  colour. 

The  gas  is  easily  procured  by  boiling  hydrochloric  acid  with  black  oxide  of 
manganese. 

To  obtain  chlorine  from  salt,  the  latter  is  first  mixed  with  the  black  oxide 
of  manganese,  and  the  sulphuric  acid,  diluted  with  water,  is  then  added.  The 
proportions  are  4  parts  by  weight  of  salt,  3  of  black  oxide  of  manganese,  io| 
sulphuric  acid  previously  diluted  with  7  of  water.  When  these  materials  are 
carefully  heated,  the  following  change  occurs: 

2NaCl  +  MnO;  +  3H2S04  =  Cl*  +  2Na2S04  +  MnS04  -+  2H20 

■'odic  Manganic  Sulphuric  Chlorine  Hydrosoclic  Manganose  Water, 

chloride.  dioxide.  acid.  gas.  sulphate.  sulphate. 

The  gas  must  be  carefully  collected,  and  even  the  first  portions  mixed  with 
air  should  be  passed  into  a  spare  jar.  If  by  accident  the  chlorine  is  inhaled, 
it  causes  the  most  violent  irritation  of  the  air-passages,  and  this  occurs  fre¬ 
quently  when  the  chlorine  is  largely  diluted  with  air,  so  that  no  inexperienced 
manipulators  (boys,  for  instance)  should  be  allowed  to  make  it  without  a  proper 
person  to  assist  them.  When  very  largely  diluted  with  air,  the  odour  is  not 
disagreeable,  reminding  one  of  the  smell  of  the  sea. 

Chlorine  is  much  heavier  than  air;  100  cubic  inches  weigh  773  grains  at 
6o°  F.,  30  in.  bar.  The  density  of  this  gas  being  l\  times  greater  than  air, 
it  may  be  collected  by  displacement  like  carbonic  acid,  and,  as  recommended 
in  the  collection  of  ammonia,  it  is  better  to  deprive  the  chlorine  of  moisture 
by  passing  it  through  a  Wolfe’s  bottle  containing  a  small  quantity  of  sulphuric 
acid  or  calcic  chloride. 

The  operator  who  employs  this  method  must  be  very  careful,  and  probably, 
to  prevent  accident,  it  is  better  to  put  warm  water  in  the  pneumatic  trough, 
and  use  that  in  preference  to  the  displacement  method,  because  water  at  6o° 
dissolves  quite  twice  its  volume  of  chlorine,  and  thus  all  danger  may  be 
avoided  by  being  able  to  watch  the  collection  of  the  gas. 

A  lighted  taper  placed  in  chlorine  gas  burns  with  a  reddish  flame,  an 
abundance  of  smoke  being  produced,  in  consequence  of  the  chlorine  combining 
with  the  hydrogen,  whilst  the  carbon  is  deposited  in  part. 


CHLORINE. 


621 


The  great  affinity  (or  desire  to  combine)  between  hydrogen  and  chlorine  is 
shown  in  a  very  striking  manner  when  equal  volumes  of  the  two  gases  are 
placed  in  a  thin  bulb  of  glass.  If  this  bulb  be  held  in  a  red  light  produced 
by  passing  the  electric  light  through  red  glass,  no  change  occurs;  but  directly 
the  violet  rays,  obtained  in  excess  by  passing  the  light  through  violet  glass, 
are  allowed  to  fall  upon  the  mixed  gases,  they  explode,  and  hydric  chloride  is 
produced. 


Fig.  485. — Preparation  and  collection  of  Chlorine  by  displacement. 

If  the  eyes  are  protected  by  a  screen  of  wire  gauze  held  before  the  bulb,  no 
harm  can  occur  from  the  bits  of  very  thin  glass. 

Hydrogen  is  now  regarded  as  a  metal,  and  analogy  indicates  more  “  pre¬ 
sumptive  evidence  ”  that  this  is  the  case,  because  other  metals,  though  they 
do  not  explode  with  chlorine,  are  quite  ready  to  burn,  and  do,  in  fact,  take  fire 
when  sprinkled  in  fine  powder  into  this  gas,  viz.,  finely-powdered  antimony, 
copper,  and  gold  in  leaf,  also  arsenic,  likewise  phosphorus. 

Chlorine  has  very  powerful  bleaching  properties,  and  is  in  effect  an  oxi¬ 
dizing  agent.  It  is  always  ready  to  unite  with  the  hydrogen  of  water:  the 
latter  undergoing  decomposition,  oxygen  is  eliminated;  and  this  in  the  nascent, 
condensed  state,  like  ozone,  destroys  many  vegetable  colours. 

A  little  solution  of  sulphate  of  indigo  is  rapidly  bleached  when  shaken  with 
some  chlorine  gas. 

Chlorine  gas  unites  with  oxygen  in  various  proportion, 

1.  Hypochlorous  anhydride,  Cl20  =  87. 

2.  Chlorous  anhydride,  Cl203=ii9. 

3.  Chloric  peroxide,  C102=67’5. 

From  the  two  first,  by  union  with  hydrogen,  are  the  following: 

1.  Producing  hypochlorous  acid,  HC10=52'5. 

2.  „  chlorous  acid,  H  CIO,. =68’). 

3.  „  no  known  acid  yet  obtained. 

4.  (No  corresponding  oxide  of  chlorine  yet  discovered)1,  producing  chloric 
acid,  HC10,  =  84-5. 

5.  (No  corresponding  oxide  of  chlorine  yet  discovered)-,  producing  per¬ 
chloric  acid,  HC104=ioo’5. 

The  Compounds  of  Chlorine  with  Hvdrogen. 

Hydric  Chloride  (Spirit  of  Salt),  Hydrochloric  Acid  (Muriatic 
Acid),  HCl  =  36-5. — As  already  stated,  equal  volumes  of  chlorine  and  hy_ 


622 


CMEMISTR  Y 


drogen  exposed  to  the  strong  light  of  day  or  violet  light,  combine  and  form 
the  same  volume  of  hydric  chloride.  This  important  acid  is  prepared  by  dis¬ 
tilling  metallic  chlorides  with  sulphuric  acid,  and,  of  course,  the  cheapest  is 
sodic  chloride,  or  common  salt.  The  following  equation  explains  the  decom¬ 
position: 

NaCl  +  S04H2  =  HC1  +  NaHSO* 

Sodic  Sulphuric  Hydrochloric  Sodic 

chloride.  acid.  acid  sulphate. 

The  same  apparatus  (Fig.  483,  p.  567)  may  be  used  for  dissolving  hydro¬ 
chloric  acid  in  water,  and  therefore,  being  so  soluble  in  the  latter,  it  must  be 
collected  in  the  mercurial  trough,  or  by  displacement  in  dry  bottles.  A  hun¬ 
dred  cubic  inches  at  6oJ  F.,  30  in.  bar.,  weigh  39'64  grains. 

Under  a  pressure  of  forty  atmospheres  it  is  condensed  into  a  fluid. 

The  ordinary  solution  in  water  as  sold  in  the  shops  is  an  almost  colourless 
fluid.  The  strongest  commercial  acid  contains  4-2  per  cent,  of  real  acid,  and 
has  a  specific  gravity  of  r2io.  It  is  impure,  and  contains  iron,  arsenic,  &c. 

The  gas  extinguishes  flame,  and  is  not  combustible.  The  solution  of  the 
acid  gas  in  water  is  most  useful  for  analytical  and  other  purposes  in  the 
laboratory. 

The  compound  of  chlorine  with  nitrogen  (HC12N,  C13N),  called  chloride  of 
nitrogen,  is  most  dangerous  and  explosive,  and  should  never  be  prepared,  as 
it  is  running  a  useless  risk,  the  properties  of  the  compound  being  already 
known. 

Chlorine  also  unites  with  carbon,  forming  at  least  four  distinct  compounds. 

- ♦ - 


IODINE. 

Symbol,  I.  Atomic  weight,  127. 

Discovered  originally  by  Courtois  in  the  waste  liquors  obtained  in  the  manu¬ 
facture  of  carbonate  of  soda  (sodic  carbonate)  from  the  lixiviation  of  the 
ashes  of  seaweed,  Iodine  is  prepared  from  kelp,  the  fused  ashes  of  burnt  sea¬ 
weed,  and  is  largely  manufactured  on  the  western  shores  of  Scotland  and  Ire¬ 
land.  The  kelp  is  first  broken  up  into  small  pieces,  and  digested  with  water; 
the  latter  dissolves  about  one-half,  consisting  of  the  chlorides  and  carbonate  of 
soda,  also  chloride  of  potassium  and  iodide  of  sodium  (sodic  iodide)  and  other 
salts ;  these  are  in  great  measure  deposited  by  evaporation  and  crystallization, 
and  as  the  iodide  of  sodium  is  the  least  solulDle,  it  remains  behind  in  what  is 
called  the  “mother  liquor”  or  “bittern;”  this,  placed  in  a  proper  vessel  and 
distilled  with  black  oxide  of  manganese  and  sulphuric  acid,  in  the  same 
manner  as  already  described  in  the  preparation  of  chlorine  from  salt,  oxide  of 
manganese,  and  sulphuric  acid  (p.  568),  yields  the  violet  vapours  of  iodine,— 
so  called  from  the  Greek  purple. 

An  experiment  on  the  small  scale  may  be  made  by  gently  heating  a  little 
solution  of  iodide  of  potassium  in  a  flask  with  oxide  of  manganese  and  sul¬ 
phuric  acid,  when  the  iodine  is  rendered  apparent  by  the  colour  it  imparts  to 
the  air  in  the  upper  part  of  the  flask.  (Fig.  486.) 

Iodine  condenses  into  a  dark  grey  solid,  having  a  brilliant  metallic  lustre. 
It  is  extremely  volatile,  rising  in  vapour  below  the  fi'eezing-point  of  water:  it 


IODINE. 


623 


freezes  at  225°,  and  boils  at  3470,  emitting  an  odour  very  much  like  that  of 
chlorine.  It  has  feeble  bleaching  powers,  and  is  slightly  soluble  in  water. 

It  attacks  certain  metals,  forming 
iodides  with  them,  and  it  may  be  again 
separated  by  chlorine.  Starch  is  the  most 
delicate  test  for  iodine,  with  which  it  forms 
a  purple  compound.  The  colour,  obtained 
by  pouring  a  little  tincture  of  iodine  into 
a  flask  containing  some  starch,  disappears 
when  the  fluid  is  boiled,  but  returns  again 
after  it  has  cooled.  Iron  or  zinc  filings 
placed  with  iodine  and  water  in  a  beaker 
glass  are  soon  converted  into  iodides  and 
dissolved  in  the  water. 

Phosphorus  takes  fire  when  brought  into 
contact  with  iodine.  Iodine  is  used  exten¬ 
sively  in  medicine ;  but  another  and  most 
important  application  of  this  element  de¬ 
serves  special  notice  here  in  connection 
with  the  art  of  photography,  and  the  Author 
is  indebted  to  his  friend,  Mr.  John  Spiller, 

Hon.  Sec.  of  the  Photographic  Society,  for  Fig.  486. — Production  of  Iodine 
the  following  rdsumd.  Vapour  from  Potassium  Iodide. 


The  Art  of  Photography. 

The  invention  cf  Photography  as  a  practical  art  may  be  said  to  date  from 
the  year  1839,  when  M.  Daguerre,  in  France,  and  the  Hon.  H.  Fox  Talbot,  in 
this  country,  described  almost  simultaneously  the  respective  processses  which 
have  since  been  identified  with  their  names.  The  daguerreotype  is  commonly 
known  as  the  process  of  obtaining  a  photographic  impression  upon  a  highly 
polished  silver,  or  electro-silver,  plate,  the  surface  of  which  is  rendered  sensi¬ 
tive  to  light,  or  rather  to  the  actinic  principle  of  the  sun’s  rays,  either  by  the 
action  of  iodine  alone  or  a  mixture  of  bromine  and  iodine.  Exposing  the 
plate  so  prepared  to  light  in  a  properly  constructed  camera  obscura,  and  after¬ 
wards  rendering  manifest  the  graduated  change  induced  upon  the  coated  sur¬ 
face  of  the  metal  by  placing  it  under  the  influence  of  mercury  vapour,  which 
then  is  found  to  attach  itself  most  abundantly  to  those  parts  of  the  image 
where  the  light  has  acted  with  the  greatest  intensity,  thereby  forming  a  lustrous 
amalgam,  which  adheres  firmly  to  the  plate,  even  when  the  excess  of  unaltered 
iodide  of  silver  is  removed  by  washing  with  an  aqueous  solution  of  hypo- 
sulphate  of  soda  or  other  chemical  solvent.  The  daguerreotype  image  is  sharp 
and  delicate,  and  when  coloured  of  a  warmer  tone  by  the  final  application  of 
a  gold  salt  (using  by  preference  the  sal  d'or  of  MM.  Fordos  and  Gelis),  is 
admirably  adapted  to  portraiture,  to  the  delineation  of  microscopical  subjects, 
and  to  the  recording  of  celestial  phenomena.  Its  chief  drawback  lies  in  the 
circumstance  that  the  silver  plates  are  liable  to  become  tarnished  in  the 
course  of  time,  however  carefully  mounted,  and,  further,  that  these  photo¬ 
graphs  are  somewhat  difficult  of  multiplication. 

Mr.  Talbot’s  process,  originally  known  as  the  “  calotype,"  but  afterwards 
named  in  honour  of  the  inventor  the  “Talbotvpe,”  depends  likewise  upon  the 


624 


CHEMISTR  Y 


sensitiveness  to  light  of  the  iodide  of  silver ;  but  the  mode  of  producing  the 
argentic  compound,  the  medium  upon  which  it  is  spread,  and  the  process  of 
developing  the  latent  image ,  are  so  totally  different,  that  it  must  be  regarded 
as  a  specifically  distinct  application  of  chemical  science. 

Plain  or  waxed  paper  is  immersed  in  a  solution  of  iodide  of  potassium,  and 
after  a  few  minutes  removed,  drained,  and  hung  up  to  dry.  In  this  condition 
it  is  stored  ready  for  use,  and  may  be  sensitized  by  being  floated  on  a  solution 
of  nitrate  of  silver  of  a  sufficient  degree  of  concentration  to  leave  an  excess 
of  the  latter  in  the  pores  of  the  paper,  and  necessarily  in  immediate  contact 
with  the  precipitated  particles  of  iodide  of  silver.  Whilst  still  slightly  moist, 
the  sheets  of  paper  are  enclosed  in  suitable  dark  slides,  and  are  ready  for 
exposure  in  the  camera ;  or  this  operation  may  be  deferred  for  any  time  short 
of  twenty-four  hours.  The  pictures  are  developed  by  dim  candlelight,  or  in  a 
room  from  which  all  but  the  yellow  non-actinic  rays  of  daylight  are  cut  off 
by  the  use  of  deep  orange  panes  of  glass  or  curtains  of  yellow  calico,  by  the 
following  process :  Gallic  acid,  in  aqueous  or  weak  acetic  solution,  is  first 
washed  over  the  paper,  and,  as  soon  as  the  photographic  image  has  become 
distinctly  visible,  a  mixture  of  gallic  acid  and  aceto-nitrate  of  silver  is  applied, 
which  gradually  augments  the  intensity  of  the  developed  image  until  the  high 
lights  in  the  original  are  represented  in  the  picture  by  intense  blacks,  and  all 
the  gradations  of  shading  appear  to  be  truthfully  rendered,  but  inversely,  in 
the  negative.  Washed  and  fixed  by  the  application  of  hyposulphate  of  soda, 
as  suggested  by  Sir  John  Herschel,  the  operator  is  in  the  possession  of  a  per¬ 
manent  record,  from  which  an  innumerable  succession  of  positive  pictures, 
true  to  nature,  may  be  obtained  by  sun-printing  upon  paper  prepared  with  the 
chloride  of  silver,  as  afterwards  explained.  The  peculiar  advantages  of  the 
talbotype  were  the  facilities  it  afforded  to  the  landscape  photographer,  who, 
preparing  his  paper  early  in  the  morning,  could  always  rely  upon  obtaining  a 
number  of  good  negatives  by  development  in  the  evening.  The  comparatively 
long  period  required  for  exposure  in  the  camera  (from  five  to  ten  minutes)  ne¬ 
cessarily  limited  the  use  of  this  process  to  objects  of  still  life  ;  but  great  results, 
even  in  portraiture,  were  obtained  by  those  who  perseveringly  devoted  them¬ 
selves  to  the  surmounting  of  a  number  of  mechanical  difficulties  connected 
with  the  selection  of  the  paper  and  its  mode  of  preparation.  An  early  im¬ 
provement  consisted  in  the  use  of  the  argento-iodide  of  potassium,  as  pre¬ 
pared  by  dissolving  iodide  of  silver  in  a  tolerably  concentrated  solution  of 
iodide  of  potassium.  This  double  salt  applied  to  the  paper  as  a  single  wash 
furnished  the  means  of  preparing  a  superior  description  of  iodized  paper  of  a 
fi  :e  primrose  tint,  by  simple  immersion,  partial  drying,  and  afterwards  floating 
on  water  to  effect  the  removal  of  the  alkaline  iodide.  With  this  material  a 
very  weak  gallo-nitrate  of  silver  was  commonly  employed  for  sensitizing,  and 
the  papers  after  exposure  showed  a  faint  image  prior  to  being  subjected  to  the 
development  process  already  described. 

The  collodion  process,  invented  by  Mr.  Scott  Archer  in  1851,  has  almost 
entirely  superseded  the  two  earlier  systems  of  photography.  It  cannot  be 
said,  however,  to  be  altogether  independent  of  Mr.  Fox  Talbot’s  original 
principle,  for  the  same  condition  of  iodide  of  silver  is  employed,  and  very 
similar  methods  of  development  and  fixing  are  resorted  to.  The  pictures  are 
obtained  upon  glass  plates  coated  with  a  film  of  exquisitely  sensitive  material, 
consisting  of  particles  of  newly  precipitated  iodide  of  silver,  supported  in  a 
transparent  network  of  pyroxyline  or  gun  cotton,  as  left  by  the  evaporation  of 


PHOTOGRAPHY. 


625 


the  ethereal  mucilaginous  material  now  so  well  known  under  the  name  of 
collodion.  For  the  production  of  this  film  of  iodide  of  silver,  a  suitable  quantity 
of  iodide  of  potassium,  or  of  cadmium,  is  dissolved  in  alcohol  and  mixed  with 
the  plain  collodion,  and  the  necessary  silver  is  supplied  by  immersion  of  the 
coated  glass  plate  in  an  upright  “dipping  bath  ”  of  nitrate  of  silver.  Removed 
after  a  few  minutes’  contact,  the  plate  is  ready  fcr  the  camera,  and  should  be 
exposed  without  delay.  Upon  being  taken  back  to  the  operating-room  to 
undergo  the  process  of  development,  there  is  absolutely  nothing  in  the  shape 
of  a  picture  visible  upon  the  plate  until  the  developer  is  applied,  which  solu¬ 
tion  may  either  consist  of  the  green  sulphate  of  iron,  or  a  dilute  solution  of 
pyrogallic  acid  in  water  rendered  slightly  acid  with  acetic  or  other  organic 
acid.  The  operation  of  these  chemical  agents  is  powerfully  reducing,  and  they 
consequently  effect  the  reduction  of  the  soluble  argentic  salt  remaining  in 
excess  upon  the  plate,  the  particles  of  finely-divided  metallic  silver  so  precipi¬ 
tated  being  deposited  by  preference  upon  the  nuclei  of  altered  molecules  of 
iodide  of  silver,  with  gradations  varying  according  to  the  intensity  of  the 
light  which  has  acted  on  those  parts.  Thus,  then,  is  obtained,  with  proper 
exposure  in  the  camera,  an  exquisitely  delicate  negative  image  in  pure  silver 
upon  a  stratum  of  collodion,  containing  still  some  yellow  iodide  of  silver  in 
admixture.  The  latter  is  removed  by  washing  with  a  solution  of  hyposulphate 
as  before,  and  the  plate  is  well  rinsed,  dried,  and  protected  with  a  coating  of 
varnish. 

From  the  negatives,  whether  obtained  by  the  collodion  or  the  calotype  pro¬ 
cess,  a  great  number  of  positive  impressions  may  be  prepared  by  following 
the  manipulation  of  what  is  called  the  printing  process.  For  this  purpose  it 
is  usual  to  employ  the  chloride  of  silver  spread  upon  paper  with  an  addition 
of  egg  albumen  and  an  excess  of  the  nitrate  of  silver. 

The  ordinary  mode  of  proceeding  consists  in  applying  to  one  side  of  a  sheet 
of  paper  a  mixture  of  well-beaten  white  of  egg,  salt,  and  a  proportion  of  water 
varied  according  to  the  degree  of  lustre  desired  in  the  finished  photographs : 
for  general  purposes  the  following  instructions  may  be  followed : 

White  of  egg  .  .  •  •  •  .  10  oz. 

Water . 5  » 

Common  salt  .  .  .  .  •  •  i  » 

For  landscapes  and  portraits  of  large  size  the  quantity  of  albumen  may  be 
advantageously  diminished,  whilst,  on  the  other  hand,  it  may  often  be  neces¬ 
sary  to  limit  the  addition  of  water  when  the  maximum  degree  of  sensitiveness 
and  delicate  rendering  of  detail  in  cartes  de  vistte  or  other  small  prints  are  the 
objects  sought.  The  mixture  of  materials  above  prescribed  is  poured,  without 
agitation,  into  a  fiat  dish,  and  one  side  of  the  paper  is  then  slowly  laid  down 
upon  the  surface  of  the  salted  albumen.  After  two  minutes’  contact  the  sheet 
is  again  carefully  removed,  and  hung  up  to  drain  and  dry.  In  this  state  the 
salted  albumen ized  paper  may  be  preserved  for  a  great  length  of  time,  and 
when  required  for  use,  it  is  necessary  to  float  it  for  two  or  three  minutes  upon 
a  50-grain  solution  of  nitrate  of  silver. 

In  order  to  perform  this  and  most  of  the  subsequent  operations  with  suc¬ 
cess,  it  is  customary  to  screen  the  light  entering  the  windows  of  the  photo¬ 
graphic  room  by  interposing  one  or  more  folds  of  yellow  calico;  for,  when 
dry,  the  sensitized  paper  will  become  bronzed  or  blackened  by  a  comparatively 
short  exposure  to  the  sun.  In  this  sensitized  condition,  the  prepared  side  of 

40 


6  26 


CHEMISTRY. 


the  paper  is  brought  into  contact  with  the  collodion  face  of  the  negative,  and 
the  two  held  together  under  slight  pressure  in  a  properly  constructed  printing- 
frame,  in  which  it  is  now  ready  to  be  exposed  to  the  light,  observing  only  the 
precaution  of  not  subjecting  the  varnished  negative  to  the  direct  and  hot  rays 
of  a  midsummer  sun.  Examined  by  lifting  one-half  of  the  hinged  back  and 
the  paper  from  the  face  of  the  negative,  the  progress  o.  the  printing  operation 
may  be  watched,  and  interrupted  at  the  proper  stage— when  the  intensity  of 
the  print  has  become  slightly  deeper  than  the  finished  result  is  required  to  be. 
At  the  end  of  a  day’s  work  it  is  customary  to  wash,  tone,  and  fix  the  prints, 
which  is  carried  out  by  immersing  in  water,  for  ten  or  twenty  minutes,  the 
prints  so  obtained,  pouring  off  the  excess  of  nitrate  of  silver  solution,  and 
leaving  them  in  a  fresh  supply  of  water,  ready  for  the  toning  operation. 

Take  Chloride  of  gold  .....  4  grains 

Bicarbonate  of  soda  .  .  .  .  ) 

Acetate  or  phosphate  of  soda  .  .  )  ^  ” 

Water . 1  pint 

The  washed  prints  are  separately  transferred  to  this  solution,  and  immersed 
for  a  period  of  time  (two  or  three  minutes)  sufficient  to  effect  a  change  of 
colour  from  foxy  red  to  bluish  purple.  When  this  stage  is  reached  they  must 
be  quickly  removed  into  a  capacious  dish  of  water,  and,  thus  toned,  are  ready 
for  the  fixing  bath,  composed  of 

Hyposulphite  of  soda  .  .  .  .  4  oz. 

Water  .......  1  pint 

They  will  need  to  be  very  thoroughly  washed  by  immersion  either  in  a  run¬ 
ning  stream  of  water,  or  in  dishes  the  contents  of  which  are  frequently  changed. 
The  prints  when  dry  are  trimmed  and  mounted. 

Other  systems  of  photographic  printing  are  occasionally  adopted;  thus,  in¬ 
stead  of  employing  the  albumenized  paper  just  now  described,  the  use  of  plain 
salted  paper  for  a  small  surface  is  resorted  to,  following  a  similar  treatment 
in  the  printing,  toning,  and  fixing  operations;  or,  lastly,  a  somewhat  novel 
mode  of  reproduction  consists  in  making  use  of  the  very  beautiful  invention 
of  Mr.  G.  Wharton  Simpson,  known  as  the  collodio -chloride  process.  For 
this  purpose  a  collodion,  specially  prepared  from  chloride  of  strontium  and 
nitrate  of  silver  in  a  vehicle  containing  the  constituents  of  plain  collodion,  is 
found  to  possess  the  singular  property  of  holding  in  suspension  for  a  great 
length  of  time  the  impalpable  particles  of  chloride  of  silver  produced  by  the 
admixture  of  the  two  above-mentioned  salts.  Preserved  always  in  the  dark, 
this  collodio-chloride  preparation  is  poured  over  a  plate  of  white  enamelled 
glass,  the  coated  side  of  which,  when  dry,  is  placed  in  contact  with  the  nega¬ 
tive  to  be  printed,  and  the  delicate  image  resulting  from  its  exposure  to  light 
is  fixed  in  the  same  manner  as  an  ordinary  collodion  picture. 

Wonderfully  fine  results  are  obtained  also  by  certain  systems  of  camera 
printing,  or  inversion  of  the  process  by  which  the  glass  negative  is  originally 
obtained.  The^e  developed  pictures,  toned  with  gold  and  mounted  with  an 
opaque  white  gelatine  backing,  have  attracted  much  attention  under  the  name 
of  “  Eburneum  ”  photographs.  If  otherwise  treated  as  transparencies,  they 
become  very  suitable  for  exhibition  in  the  magic  lantern,  or,  with  ground  glass 
behind,  they  have  been  made  to  do  duty  in  the  stereoscope. 

The  so-called  “  carbon  photographs  ”  are  prints  obtained  upon  a  tissue  of 


BROMINE. 


62  7 


gelatine  and  bichromate  of  potash,  with  which  has  been  incorporated  carbon 
itself  in  the  form  of  lampblack  or  Indian  ink,  or  any  equivalent  dark-coloured 
pigment.  By  exposure  to  light  the  gelatine  becomes  hardened  and  insoluble, 
so  that  in  the  high  lights  of  the  picture  much  of  the  colouring  matter  is  locked 
in  the  material,  whilst  in  the  prot:cted  portions  of  the  print  all  the  gelatine 
and  pigment  washes  away,  leaving  the  white  paper  or  other  basis  of  the 
transfer  freely  visible,  and  the  half-tones  are  properly  represented  by  gradu¬ 
ated  layers  of  altered  gelatine,  the  varying  thicknesses  of  which  are  dependent 
upon  the  intensity  of  the  light’s  action. 

The  latest  modification  of  the  principle  involved  in  the  carbon  printing 
process  of  Mr.  Swan  is  one  by  which  the  final  results  are  obtained  by  mecha¬ 
nical  printing,  from  a  metal  block  which  bears  the  impress  of  the  delicate 
gelatine  relief  resulting  from  a  mode  of  working  similar  to  that  just  now  de¬ 
scribed.  This  metallic  plate  is  charged  with  a  liberal  supply  of  warm  ink 
(composed  of  gelatine  and  suitable  pigments),  then  covered  with  white  paper, 
and  pressure  is  immediately  applied  for  the  purpose  of  driving  out  all  the  ex¬ 
traneous  ink.  When  cold,  the  print  is  lifted  from  the  metal  block,  and  fixed 
by  immersion  in  alum-water,  which  renders  the  gelatine  completely  insoluble. 
This  mode  of  proceeding  is  the  invention  of  Mr  Walter  B.  Woodbury,  and 
the  resulting  proofs  are  commonly  known  as  “  Woodburytypes.”  Their  ex¬ 
quisite  delicacy  brings  them  into  favourable  comparison  with  the  best  results 
of  the  silver  printing  process;  and  it  will  be  remarked  that  when  the  gelatine 
matrix  is  once  procured,  the  subsequent  operations  are  entirely  independent 
of  the  action  of  light.  . 

Iodine,  like  chlorine,  unites  with  hydrogen,  forming  an  acid  called  hydri- 
odic  acid  or  hydric  iodide.  The  symbol  of  this  acid  is  HI,  and  its  atomic 
weight  128. 

Hydriodic  acid  is  a  gas  which  fumes  strongly  when  brought  in  contact  with 
the  air:  it  is  very  heavy,  the  specific  gravity  being  4‘443-  Like  hydrochloric 
acid,  it  may  be  collected  by  displacement,  and  is  composed  of  one  volume  of 
hydrogen  and  one  of  iodine,  forming  two  volumes  of  hydriodic  acid. 

There  are  some  oxides  of  iodine  and  two  important  acids: 

Iodic  acid  or  hydric  iodate  (symbol,  HI03); 

Hydric  periodate  or  periodic  acid  (symbol,  HIO«); 

Iodic  pentoxide  (symbol,  I205) ; 

and  iodine  appears  to  have  a  stronger  affinity  or  attractive  power  for  oxygen 
than  either  chlorine  or  bromine.  It  unites  also  with  chlorine  and  bromine, 
and  forms  an  explosive  compound  with  nitrogen,  NI3,  in  which  an  analogy  in 
molecular  composition  to  ammonia  is  at  once  apparent,  three  atoms  ol  hydro¬ 
gen  being  replaced  by  three  of  iodine. 


BROMINE. 

Symbol,  Br.  Atomic  weight,  80. 

This  element  (perhaps  a  quasi  element,  for  there  is  every  probability  that 
it  will  one  day  be  resolved  into  another  and  more  elementary  condition)  bears 
a  close  resemblance  to  chlorine,  and  has  many  properties  in  common  with 
that  element.  It  was  discovered  by  Balard  in  1826,  in  the  same  liquid,  ‘  bittern, 

4t>  —  2 


628 


C HE  MI  ST R  Y. 


which  furnished  iodine,  with  this  exception,  that  Balard’s  “  bittern  ”  came  from 
the  mother  liquor  of  the  salt  marsres  ol  Montpellier. 

Near  Kreuzenach,  at  a  place  called  Theodorshall,  is  a  salt-spring,  and  from 
this  water  a  considerable  quantity  of  bromine  is  obtained. 

The  iodine,  as  in  the  instance  of  the  mother  liquor  of  varec,  is  first  got  rid 
of  by  passing  chlorine  gas  into  the  liquor  until  a  sample  gives  no  precipitate 
with  chlorine;  the  residual  fluid  is  then  mixed  with  black  oxide  of  manganese 
and  sulphuric  acid,  and  distilled,  and  the  same  kind  of  change  that  occurs  in 
the  preparation  of  chlorine  or  elimination  of  iodine  takes  places  in  this  case 
also,  and  bromine  is  obtained. 

2MgBr+2MnO-f  2H2S04  =  Br2  +  Mg2S04  +  Mn2S04  +  2H20. 

Bromine  is  extremely  volatile :  a  few  drops  thrown  into  a  bent  tube  soon 
fill  it  with  red  vapour.  It  is  a  non-conductor  of  electricity.  At  — 220  C.  it 
assumes  the  solid  state,  and  is  then  of  a  dark  greyish  lead-colour,  with  a  par¬ 
tial  metallic  lustre. 

The  smell  of  bromine  is,  like  chlorine,  verv  suggestive  of  the  odour  of  sea 
air.  In  a  concentrated  state  the  vapour  is  irritating,  and  it  was  from  this  cir¬ 
cumstance  that  the  element  was  named  a  stink. 

The  specific  gravity  of  bromine  in  the  state  of  vapour  is  5 '540 ;  in  its  ordi¬ 
nary  liquid  state  the  specific  gravity  is  3*  1 87  at  a  temperature  of  320  F.  Bro¬ 
mine,  like  chlorine,  is  a  powerful  bleaching  agent:  it  is  very  corrosive,  attack¬ 
ing  cork  and  wood,  which  are  changed  yellow  and  become  disintegrated  and 
rotten.  A  very  little  drop  will  kill  a  small  animal.  The  same  atomic  relation 
to  hydrogen  observed  with  chlorine  and  iodine  occurs  with  this  element. 

Hydrobromic  acid  or  hydric  bromide  (symbol,  HBr;  atomic  weight,  81) 
consists  of  equal  measures  of  hydrogen  and  bromine  vapours  united,  but  re¬ 
taining  the  same  volume.  The  compounds  of  oxygen  and  bromine,  although 
numerically  less,  are  very  similar  to  those  of  chlorine  and  oxygen. 

Hypobromous  acid,  HBrO  ; 

Bromic  acid  or  hydric  bromate,  HBrOs. 

Perbromic  acid  or  hydric  perbromate,  HBrO, 

There  is  also  a  compound  of  bromine  with  chlorine  called  bromous  chloride 
(BrCl3),  and  a  detonating  oily  fluid,  bromide  of  nitrogen,  analogous  to  chloride 
of  nitrogen.  A  fluoride  of  bromine  likewise  exists :  in  fact,  bromine  unites 
with  all  the  elementary  bodies.  Altogether,  bromine  holds  an  intermediate 
position  between  chlorine  and  iodine.  It  can  expel  the  latter  element  from 
certain  compounds,  and  is  in  its  turn  expelled  by  chlorine. 

If  the  atomic  weight  of  iodine  be  added  to  that  of  chlorine,  and  divided  by 
two,  the  mean  is  as  nearly  as  possible  the  atomic  weight  of  bromine. 


FLUORINE. 

Symbol,  F.  Atomic  weight,  19. 

This  element  appears  to  have  evaded  the  usual  searching  powers  of  the 
analytical  chemist,  and  for  a  long  time  could  not  be  procured  in  the  elemen¬ 
tary  state.  It  seems,  however,  to  be  satisfactorily  determined  that  it  can  be 
liberated  from  the  trammels  of  combination  by  acting  on  dry  argentic  fluoride 
or  silver  fluoride  with  dry  iodine ;  it  then  appears  as  a  colourless  gas,  which 


CARBON. 


629 


has  no  power  upon  glass,  and  is  rapidly  absorbed  by  a  sclut;on  of  potash,  but 
remains  permanent  over  mercury. 

Fluor  spar  is  found  in  Derbyshire  and  in  all  the  galena  (plumbic  sulphide) 
veins  which  traverse  the  coal  formations  of  Durham,  Cumberland,  and  other 
places,  and  is  most  frequently  crystallized  in  the  cubic  form.  The  red  varieties 
have  been  called  false  ruby,  the  yellow  false  topaz ,  the  green  false  emerald , 
and  the  blue  false  sapphire  and  amethyst.  The  variety  of  fluor  spar  that  be¬ 
comes  phosphorescent  when  heated  is  called  “  chlorophane,”  from  the  green 
light  it  emits 

Because  it  has  been  used  by  the  metallurgists  as  a  flux  for  ores,  particularly 
those  of  iron  and  copper,  it  derives  the  name  of  “ fluor ,”  from  fluo  to  flow ; 
its  modern  scientific  name  is  calcium  fluoride  (CaF2).  Fluorine  is  also  con¬ 
tained  in  the  mineral  termed  cryolite  (3NaF,  A1F3),  a  double  salt  of  sodium  and 
aluminium  fluoride,  and  an  important  source  of  the  metal  aluminium.  As  the 
teeth  contain  a  minute  quantity,  it  is  evident  that  the  body  is  supplied  with 
this  element  from  the  foods  required  for  the  support  of  man. 

The  most  important  compound  is  that  which  it  forms  with  hydrogen— called 
hydro-fluoric  acid  or  hydric  fluoride  (HF  =  2o).  It  is  obtained,  like  hydro¬ 
chloric  acid,  by  distilling  one  part  of  fluor  spar  with  three  parts  of  strong  sul¬ 
phuric  acid,  and  the  decomposition  is  represented  by  the  following  equation  : 

CaF*  +  H2S04  =  2HF  +  CaSO. 

FI  or  spar  Sulphuric  acid  =  Hydric  tluoride  Calcium  sulphate 

The  fluor  spar  and  sulphuric  acid  must  be  heated  in  a  leaden  retort,  or, 
better  still,  in  one  made  of  platinum,  and  the  vapour,  hydric  fluoride,  is  col¬ 
lected  in  a  receiver — usually  a  bent  leaden  or  platinum  tube  surrounded  with 
a  freezing  mixture.  The  metals,  lead  or  platinum,  should  be  used,  as  hydric 
fluoride  acts  so  vigorously  on  glass. 

It  would  appear  from  the  researches  of  Louzet  that  the  acid  prepared  in 
this  way  contains  water,  and  by  distilling  it  again  with  phosphoric  anhydride, 
a  colourless  gas  of  a  very  lung-exciting  nature  is  obtained,  which  does  not  act 
like  the  ordinary'  acid  on  perfectly  dry  glass.  This  acid  united  with  two  atoms 
of  water  increases  in  specific  gravity  from  roboto  ri5o  (HF,  2H20).  It  does 
not  undergo  any  change  when  distilled,  and  boils  at  248°  F.  This  acid  acts 
upon  a  great  number  of  metals,  its  hydrogen  being  displaced  by  them.  The 
acid  is  used  for  etching  on  glass,  and  is  now  (like  other  once  rare  chemical 
compounds)  employed  most  skilfully  in  the  formation  of  elegant  patterns  on 
that  vitreous  body. 

- ♦ - 

CARBON. 

Symbol,  C.  Atomic  weight,  12. 

Every  tyro  in  chemistry  is  now  ready  to  speak  profanely  of  the  diamond  as 
only  a  bit  of  hard  and  nearly  pure  carbon.  The  portraits  of  Faraday  and 
Wheatstone  have  already  been  given  in  this  work,  and  the  series  is  hardly 
complete  without  that  of  the  learned  man  who  has  lately,  like  Faraday,  passed 
away  from  us.  Brewster’s  name  is  introduced  here  because,  amongst  the 
thousand  and  one  clever  papers  on  scientific  subjects  that  he  wrote,  we  find 
one  devoted  to  what  he  terms  pressure  cavities  in  the  diamond,  which  will  be 
alluded  to  hereafter. 


630 


CHEMISTRY. 


Fig.  487. — Portrait  and  Signature  of  Sir  David  Brewster. 


David  Brewster  was  born  at  Jedburgh  on  the  1  ith  December,  1781,  and  died 
in  1868.  His  name  will  always  be  associated  with  the  kaleidoscope,  and  the 
discussion  of  other  and  more  abstruse  points  in  the  science  of  optics. 


CARBON. 


631 

Carbon  or  charcoal  can  be  obtained  from  various  sources.  Bone-black  or 
animal  charcoal  is  obtained  by  subjecting  bones  to  a  low  red  heat  in  closed 
iron  cylinders,  the  volatile  matter,  ammonia,  &c.,  being  allowed  to  pass  into 
proper  receivers. 

It  is  most  usefully  employed  as  a  deodorizing  agent  in  the  purification  0/ 
raw  sugar,  &c.,  and  its  deodorizing  properties  and  power  of  condensing  the 
putrid  effluvia  of  decomposing  animal  or  vegetable  matter  is  very  well  under¬ 
stood,  and  used  in  the  openings  of  the  shafts  of  sewers,  or,  more  agreeably,  in 
the  filtration  and  purification  of  water  containing  organic  matter. 

Wood  charcoal  is  now  made  very  carefully  from  willow  or  alder,  by  heating 
them  in  closed  iron  cylinders,  and,  when  prepared  in  this  manner,  is  used  in 
the  manufacture  of  gunpowder.  Common  wood  charcoal  used  for  heating 
purposes  is  prepared  in  a  ruder  fashion  by  the  charcoal-burners.  Lampblack, 
or  finely-divided  charcoal,  is  obtained  by  the  slow  combustion  of  resin  or  tar: 
these  bodies  yield  hydro-carbon,  and,  as  the  air  is  only  partially  admitted,  the 
hydrogen  is  removed,  forming  water,  whilst  the  carbon  is  deposited.  By  ex¬ 
posing  common  lampblack  to  a  red  heat  in  a  closed  iron  vessel,  the  tarry 
matter  is  then  thoroughly  ignited,  and  a  very  pure  form  of  carbon  obtained. 

Coke,  the  charcoal  of  coal,  is  made  in  large  quantities  during  the  distillation 
of  coal  in  the  manufacture  of  coal-gas. 

A  very  hard  form  of  charcoal  is  gradually  deposited  in  the  gas  retorts,  which 
is  used  instead  of  platinum  in  the  nitric  acid  cell  of  the  voltaic  battery,  called 
Bunsen’s,  and  likewise  for  the  terminals  of  the  poles  of  the  voltaic  battery  in 
the  production  of  the  electric  light.  This  kind  of  charcoal  is  sometimes 
spoken  of  as  graphite ;  but,  when  so  styled,  should  be  called  “  artificial,”  as 
the  real  graphite  is  a  natural  and  nearly  pure  form  of  carbon. 

Plumbago,  black  lead,  or  graphite  is  a  most  useful  form  of  mineral  carbon: 
it  used  to  be  obtained  from  the  mines  at  Borrowdale,  but  is  now  procured  from 
mines  in  Asia  and  other  places.  The  finer  kinds  of  plumbago  were  formerly 
boiled  in  oil,  and  then  cut  into  tables  or  pencils ;  but  now  the  dust  or  powdered 
plumbago  is  compressed  and  employed  extensively  in  the  manufacture  of  lead 
pencils.  It  is  also  used  for  brightening  grates  and  other  ironwork,  and  keeping 
them  free  from  rust.  Graphite  is  now  extensively  used  in  the  manufacture  of 
very  refractory  crucibles,  and  as  an  anti-friction  material. 

By  combining  charcoal  with  wrought  iron,  the  latter  becomes  extremely 
fusible.  If  this  compound  of  carbon  and  iron  be  melted  and  allowed  to  cool 
slowly,  it  will  be  covered  with  scales,  which  on  examination  are  found  to  be 
identical  with  plumbago  or  black  lead. 

Some  meteorites  contain  graphite  or  black  lead,  mechanically  diffused 
through  the  mass  of  iron  which  has  fallen  from  the  skies. 

Brodie  has  shown  that  by  acting  on  graphite  with  an  oxidizing  agent,  suoh 
as  chlorate  of  potash  and  sulphuric  acid,  a  product  is  obtained  that  does  not 
present  any  characteristic  different  from  that  of  ordinary  graphite.  If,  how¬ 
ever,  it  .be  heated  in  a  test-tube,  it  swells  up  and  presents  a  very  remark¬ 
able  appearance :  the  graphite  partly  oxidized  gives  off  steam,  and  returns 
again  to  its  original  condition.  Carrying  the  oxidizing  process  still  further, 
the  same  chemist  has  converted  graphite  into  graphitic  acid  (Cnhb03).  By 
acting  repeatedly  on  this  substance  with  chlorate  of  potash  and  nitric  acid,  it 
forms  perfectly  transparent  thin  crystals  :  when  a  few  of  these  are  heated  in  a 
platinum  dish,  incandescence  and  a  slight  explosion  occurs,  and  a  large  quan¬ 
tity  of  soot  is  evolved :  the  graphite,  by  the  roundabout  process  of  oxidation 


632 


CHEMISTR  Y 


and  conversion  into  graphitic  acid,  and  subsequent  heating,  is  now  changed 
to  ordinary  charcoal.  The  experiment  with  the  graphitic  acid  is  a  very  curious 
one,  the  quantity  of  charcoal  evolved  in  the  form  of  soot  is  so  enormous. 


Fig.  488. —  The  Koh-i-Noor  before  and  after  re-cutting. 

A,  the  Koh-i-Noor  before  re-cutting;  b,  back  view  of  same  after  re-cutting  by  Mr.  Coster;  c,  front 

view  after  re-cutting. 

The  diamond,  the  purest  form  of  natural  carbon,  is  well  represented  by  the 
most  costly  of  the  crown  jewels  called  the  Koh-i-Noor. 

“The  history*  of  this  gem  has  been  so  often  told  that  it  would  be  superflu¬ 
ous  to  give  any  lengthened  notice  of  it.  The  Hindoo  accounts  deduce  it  from 
the  time  of  the  god  Krischna.  We  know,  however,  for  a  certainty  that  it  was 
in  the  treasury  of  Delhi,  and  was  taken  at  the  conquest  of  that  city  by  Ala- 
ed-Din.  Thence  it  came  into  the  possession  of  the  Sultan  Baber,  of  the 
Mogul  dynasty,  in  1526.  This  prince  esteemed  it  at  the  sum  of  the  daily 
maintenance  of  the  whole  world.  The  jewel  was  seen  by  Tavernier  among 
the  jewels  of  Aurungzebe:  it  had,  however,  been  reduced  by  the  unskilfulness 
of  Hortensio  Borgio  from  793  carats  to  186  carats — the  weight  it  possessed 
at  the  Exhibition  of  1851.  The  Emperor  Aurungzebe  was  so  incensed  that 
he  refused  to  pay  Borgio  the  sum  agreed  on  for  the  cutting,  confiscated  the 
whole  of  his  possessions,  and  with  great  difficulty  was  persuaded  to  leave  him 
his  head.  Nadir  Shah,  the  conqueror  of  India,  by  means  of  an  artful  trick 
obtained  possession  of  this  stone,  and  from  the  hands  of  his  descendants  it 
passed  into  the  possession  of  Achmed  Shah.  His  son,  Shah  Sujah,  was  in 
turn  forced  to  return  it  into  the  hands  of  Runjeet  Singh.  After  the  capture  of 


*  “  Diamonds  and  Trecious  Stones  ’’  By  H  Emanuel. 


THE  DIAMOND. 


633 


Lahore,  at  the  time  of  the  Sikh  mutiny,  it  fell  into  the  hands  of  the  British 
troops,  who  presented  it  to  Her  Majesty  Queen  Victoria  on  the  3rd  of  June, 

1850. 

“This  brilliant  was  shown  at  the  Exhibition  of  1851.  It  then  had  an  irre¬ 
gular  form,  with  several  hollows  in  its  sides  and  base,  and  showed  clear  traces 
of  natural  cleavage  planes;  there  were  also  several  fissures  or  cavities  in  its 
surface.  It  was  shown  to  several  of  the  first  scientific  men  of  the  day,  Sir 
David  Brewster  among  the  number,  who  were  of  opinion  that  the  stone  pre¬ 
sented  great  difficulty  in  the  way  of  cutting.  After  much  consideration  it  was 
entrusted  to  Mr.  Coster,  of  Amsterdam,  who  expressed  himself  confident  as  to 
the  result  of  re-cutting;  and  the  event  proved  the  correctness  of  his  judgment, 
for  the  stone,  though  of  less  weight  than  before,  possesses  nearly  the  same 
size,  and  instead  of  being  a  lustreless  mass  scarcely  better  than  rock  crystal, 
it  has  become  a  brilliant  matchless  for  purity  and  fire. 

“  Thi  j  diamond  now  weighs  106-L-  carats,  and  forms  part  of  the  crown  jewels 
of  England.” 

Sir  David  Brewster  makes  the  following  remarks  on  the  Koh-i-Noor  in  hjs 
paper  in  the  “  Transactions  of  the  Royal  Society  of  Edinburgh,  1862,”  ar.d 

entitled 

“On  the  Pressure  Cavities  in  Topaz,  Beryl,  and  Diamond, 
AND  THEIR  BEARING  ON  GEOLOGICAL  THEORIES. 

“In  the  Kvh-i-Noor  diamond,  which  the  Prince  Consort  kindly  permitted 
me  to  examine  in  1852,  I  found  three  black  specks,  scarcely  visible  to  the  eye, 
but  which  the  microscope  showed  to  be  irregular  cavities  surrounded  with 
sectors  of  polarized  light.  In  the  two  smaller  diamonds  which  accompanied 
the  Koh-i-Noor  there  were  also  several  cavities  surrounded  with  luminous 
sectors,  and  the  same  polarizing  structure  which  indicated  the  operation  of 
compressing  and  dilating  forces.  In  older  to  obtain  more  information  on  this 
subject,  I  examined  nearly  fifty  diamonds  lent  me  by  Messrs.  Hunt  and  Ros- 
kell,  and  in  almost  all  of  them  I  found  numbers  of  cavities  of  the  most  singular 
forms,  round  which  the  substance  of  the  stone  had  been  compressed  and 
altered  in  a  remarkable  manner.  The  shapes  of  the  cavities  sometimes  re¬ 
sembled  those  of  insects  and  lobsters,  and  the  streaks  and  patches  of  colour  in 
polarized  light  were  of  the  most  variegated  kind.  It  seems,  indeed,  to  be  a 
general  truth  that  there  are  comparatively  few  diamonds  without  cavities  and 
flaws,  and  that  this  stone  is  a  fouler  stone  than  any  other  used  in  jewellery. 
Some  diamonds,  indeed,  derive  their  black  colour  entirely  from  the  number 
of  cavities  which  they  contain,  and  which  will  not  permit  any  light  to  pass 
between  them. 

“  Having  found  in  diamonds  so  many  pressure  cavities,  as  we  may  call  them, 
round  which  the  substance  of  the  stone  is  compressed,  I  had  some  expectation 
of  finding  them  in  other  minerals;  and  in  re-examining  the  numerous  plates 
of  topaz  in  my  possession,  I  succeeded  in  discovering  several  under  such  re¬ 
markable  circumstances  that  I  submitted  a  description  and  drawings  of  them 
to  this  society  in  1845.  In  searching  for  these  phenomena  with  the  polarizing 
microscope,  we  first  observe  four  sectors  of  polarized  light ;  and  if  the  magni¬ 
fying  power  is  sufficient,  we  shall  find  in  the  centre  of  the  black  cross  that 
separates  the  sectors  a  small  opaque  speck,  which  is  the  cavity  or  seat  ol  the 
compressing  force.  This  cavity  is  frequently  of  a  rhomboidal  form,  and  often 
only  of  the  3,000th  or  4,000th  of  an  inch  in  diameter.  It  is  always  opaque,  as 


CHEMISTR  Y 


634 


if  the  elastic  substance  which  it  contained  had  collapsed  into  a  black  powder; 
and  1  have  met  with  only  one  cavity  in  which  there  was  a  speck  of  light  in  its 
centre.  The  polarized  tint  of  the  luminous  sectors  varies  from  the  faintest 
blue  to  yellow-green;  blue  and  red  tints  of  higher  orders.  In  most  cases  the 
elastic  force  has  spent  itself  in  the  compression  of  the  topaz,  the  cavity 
remaining  entire  and  without  any  apparent  fissure  by  which  a  gas  or  liquid 
could  escape.  I  have  discovered,  however,  other  cavities,  and  these  generally 
of  a  larger  size,  in  which  the  sides  have  been  rent  by  the  elastic  force,  and 
fissures,  from  one  to  six  in  number,  propagated  to  a  small  distance  around 
them.  These  fissures  have  modified  the  doubly  refracting  structure  produced 
by  compression,  but  the  gas  or  fluid  which  has  escaped  has  left  no  solid  matter 
on  the  faces  of  fracture.” 

The  “Chemical  News”  gives,  however,  a  brief  commentary  on  the  above, 
by  stating  that  “  Mr.  Sorby  finds  that  the  supposed  cavities  in  diamonds 
described  by  Brewster  are,  in  reality,  enclosed  crystals;  and  the  conclusion 
arrived  at,  from  the  consideration  of  the  whole  structure  of  the  diamond,  is 
not  opposed  to  its  having  been  formed  at  a  high  temperature.  The  crystals 
enclosed  in  diamonds  are  frequently  seen  to  be  surrounded  by  a  series  of  fine 
radiating  cracks,  which  arc  proved  to  be  the  result  of  the  contraction  suffered 
by  the  diamond  in  solidifying  over  the  enclosed  crystal ;  and  this  explanation 
has  been  artificially  verified  by  examining  crystals  formed  in  fused  globules 
of  borax  and  glass  cooled  slowly,  when  the  same  phenomena  are  seen.” 

Compounds  of  Carbon  with  Oxygen. 

Carbonic  Acid  or  Carbonic  Dioxide. — As  all  acids  are  now  supposed  to 
denote  a  salt  of  hydrogen ,  even  the  term  “  acid  ”  when  applied  to  carbonic  aod 
would  be  incorrect,  because  the  latter  contains  no  hydrogen.  Chemists,  how¬ 
ever,  have  met  this  difficulty  by  retaining  a  part  of  the  name  by  which  it  is  so 
well  known,  viz.,  carbonic,  and  adding  thereto  “anhydride,”  to  show  that  it 
has  no  hydrogen. 

Carbonic  anhydride  (C02=44;  specific  gravity,  1  '529). — This  gas,  as  already 
stated,  is  contained  in  atmospheric  air,  and  is  easily  detected  by  exposing  some 
lime-water  in  a  dish  to  the  air.  A  pellicle  of  carbonate  of  lime,  calcic  car¬ 
bonate,  or  chalk,  is  formed,  and  therefore  a  compound  of  carbonic  dioxide 
and  calcium  oxide. 

This  gas  is  easily  obtained  by  acting  on  chalk,  marble,  limestone,  oyster- 
shells,  or  whiting,  by  dilute  nitric,  hydrochloric,  or  sulphuric  acids.  Acetic 
acid  (vinegar)  may  also  be  used. 

The  following  equation  is  a  simple  example  of  decomposition: 

CaC03  +  2HCI  =  CaCljs  -f  CO, 

Chalk.  Hydrochloric  Calcium  Carbonic 

ati  I.  chloride.  dioxide. 

Calcium  carbonate  and  hydrochloric  acid  give  carbonic  dioxide,  water,  and 
calcium  chloride. 

Carbonic  dioxide  has  a  slight  acidulous  odour,  is  colourless,  transparent, 
and  half  as  heavy  again  as  atmospheric  air.  It  was  originally  discovered  by 
Dr.  Black,  who  called  it  fixed  air.  It  is  perfectly  unrespirable.  If  an  attempt 
be  made  to  breathe  it,  the  epiglottis  closes  spasmodically,  and  suffocation 
occurs.  It  is  a  poison,  and  appears  to  act  as  a  narcotic  when  mixed  with 


CARBON  WITH  OXYGEN 


635 


a  large  quantity  of  air,  causing  drowsiness,  insensibility,  and  death  ;  hence  the 
danger  of  breathing  an  atmosphere  contaminated  with  carbonic  acid. 

In  sinking  deep  wells  and  pits  the  air  may  become  foul  from  the  breath  of 
the  workmen,  or  trom  other  causes.  The  bad  air,  containing  carbonic  dioxide, 
is,  however,  soon  removed  by  letting  down  a  closed  inverted  umbrella,  which, 
opening  with  a  spring,  is  pulled  quickly  up  and  again  lowered,  until  it  is  found 
that  a  candle  will  burn  in  every  part  of  the  pit  or  well. 

When  the  air  of  a  room  contains  T\j  per  cent,  of  carbonic  dioxide,  it  is  no 
longer  fit  for  respiration,  and  the  bad  effects  of  this  dilute  poison  is  shown  by 
the  fainting  of  delicate  women,  who  are  sometimes  peculiarly  sensitive  to  the 
action  of  this  poison. 

In  the  fermentation  of  beer  large  quantities  of  this  gas  are  evolved;  and 
many  fatal  accidents  have  been  caused  by  the  foolish  carelessness  of  the 
brewers  in  entering  vats  too  soon  after  the  beer  has  been  drawn  off.  The 
chokedamp  of  mines  owes  its  life-destroying  powers  to  the  same  cause — the 
presence  of  carbonic  dioxide,  which  follows  the  explosion  of  fire-damp  and  air 

It  is  an  erroneous  idea  to  suppose  that  carbonic  dioxide,  when  once  mixect 
with  air,  can  separate  itself  and  fall  to  the  lower  part  of  the  room:  it  remains 
mixed  by  the  law  of  diffusion,  and  the  value  of  the  law  is  thus  seen  to  be  very 
great ;  as  it  is  quite  possible  to  conceive  that  a  separation  might  take  place 
in  a  mechanical  mixture  of  air  and  carbonic  dioxide  if  this  were  not  the  case. 

A  solution  of  carbonic  dioxide  in  water  is  called  “  soda-water,”  this  beverage 
having  derived  its  name,  not  from  the  gas  which  imparts  the  refreshing,  spark¬ 
ling  character,  but  from  the  few  grains  of  sodium  carbonate  added  to  the 
fluid  contents  of  each  bottle. 

By  a  pressure  of  38'5  atmospheres,  and  at  a  temperature  of  320  F.,  carbonic 
anhydride  is  liquefied.  It  does  not  in  this  state  dissolve  freely  in  water;  but 
if  mixed  with  alcohol,  ether,  turpentine,  or  carbonic  disulphide,  solution  occurs 
very  rapidly,  and  this  fact  is  taken  advantage  of  to  produce  very  low  tempera¬ 
tures.  When  the  liquid  acid  is  allowed  to  escape  from  the  apparatus  devised 
and  constructed  by  Mr.  Robert  Addams,  the  cold  produced  is  so  intense  that 
the  liquid  acid  solidifies  in  beautiful  snow-like  flakes,  which  may  be  collected 
in  a  proper  box.  If  this  solid  carbonic  dioxide  is  mixed  with  ether,  the  tem¬ 
perature  sinks  to— 148°  F.  or  ioo°  C.,  and  if  mercury  is  placed  in  the  solution, 
it  solidifies.  A  number  of  very  pleasing  experiments  may  be  performed  with 
solid  carbonic  dioxide,  such  as  freezing  water  in  a  red-hot  vessel.  1  his  expe¬ 
riment  was  originally  performed  by  Faraday  by  placing  some  ol  the  solid  gas 
into  a  red-hot  crucible,  and,  after  pouring  in  a  little  ether,  the  mercury  is 
quickly  added,  and  in  a  few  seconds  assumes  the  solid  state.  Mercury  freezes 
at  a  temperature  of  40°  below  the  freezing-point  of  water. 

The  ordinary  gas  is  easily  collected  by  displacement,  and  may  be  poured 
from  one  vessel  to  another.  It  extinguishes  flame,  and  this  test,  with  that  of 
lime-water,  enables  the  experimentalist  to  devise  a  number  of  amusing  experi¬ 
ments,  in  which  the  breath,  the  gas  from  soda-water,  or  the  combustion  of 
charcoal  or  the  diamond,  are  found  to  put  out  the  light,  and  to  change  the  lime- 
water  milky  white  from  the  formation  and  precipitation  of  chalk.  Carbonic 
dioxide  gas  may  be  drawn  off  by  a  syphon,  or  collected  in  a  large  jar  and 
allowed  to  run  out  of  a  tap.  If  the  jar  is  a  wide-mouthed  one,  a  child  s  india- 
rubber  ball,  or  a  balloon  distended  with  air,  will  not  sink  in  the  gas,  but  re¬ 
mains  floating,  like  a  cork  in  water,  too  cubic  inches  of  carbonic  dioxide 
weigh  47'303  grains  at  6o°  F.,  30  in.  bar. 


CHEMISTRY. 


636 


A  solution  of  the  gas  in  water  reddens  blue  litmus-paper,  which  is  again 
restored  to  its  original  colour  by  boiling  the  paper  in  water,  because  the  car¬ 
bonic  acid  gas  is  driven  off  by  the  heat. 

It  is  partly  the  carbonic  dioxide  dissolved  by  the  rain  which  gradually  filters 
through  the  strata,  and  dissolves  the  calcium  carbonate  and  other  matters 
found  in  spring-water.  Carbonic  dioxide  is  also  produced  in  water  by  the  oxi¬ 
dation  of  the  organic  matter  by  the  oxygen  of  the  air.  Oxygen  and  organic 
matter  in  solution  in  water  react  upon  one  another,  and  carbonic  dioxide  is 
produced,  whilst  the  oxygen  originally  dissolved  in  the  water  is  reduced  in 
quantity. 

Various  ingenious  propositions  have  been  made  to  enable  persons  to  go  with 
impunity  into  an  atmosphere  containing  corbonic  dioxide  or  other  dangerous 
gases,  or  to  attend  on  large  voltaic  batteries  where  nitrous  fumes  are  evolved. 
The  most  practical  and  thoroughly  useful  contrivance  is  that  of  M.  Galibert, 
and  called  by  him  the  “  Patent  Respiratory  Apparatus,”  being  a  most  important 


Fig.  489. — Galibert' s  Apparatus. 


and  valuable  invention  for  the  protection  of  life  and  property  against  danger 
arising  from  fire,  also  of  persons  exposed  to  danger  from  exhalations  of  gas, 
foul  air  in  mines,  sewers,  &c.,  &c.  It  is  simple,  cheap,  and  effective. 

This  invention  has  been  successfully  introduced  throughout  the  French 
empire,  and  the  inventor  has  obtained  many  prizes  and  medals  in  acknow¬ 
ledgement  of  its  merits. 

A  reservoir,  of  the  capacity  of  five  cubic  feet,  made  of  stout  canvas,  and 


G  A  LI  BERT'S  APPARATUS. 


637 


fireproof,  is  filled  with  air  by  means  of  a  small  bellows  belonging  to  the 
apparatus,  and  placed  on  the  back  of  the  operator,  as  shown  in  the  drawing, 
being  suspended  from  braces  passed  over  his  shoulders,  and  further  held  in 
position  by  a  belt  round  the  body.  There  arc  india-rubber  tubes,  the  two  ends 
of  which  are  inserted  into  the  reservoir,  the  operator  holding  the  other  end  in 
his  mouth  by  means  of  a  mouthpiece  of  horn  to  which  they  are  attached,  thus 
enabling  him  to  breathe  freely  from  the  supply  of  air  drawn  through  the  tubes 
from  the  reservoir,  without  any  inconvenience  from  dense  smoke  or  poisonous 
gases. 

The  eyes  of  the  operator  are  covered  with  goggles,  so  fitted  as  to  effectually 
protect  them  from  any  gas  or  smoke,  and  the  nostrils  are  closed  by  a  small 
and  simple  instrument  for  that  purpose. 

The  fire  department  of  Paris  has  provided  all  its  stations  with  the  respira¬ 
tory  apparttis  of  M.  Galibcrt.  The  city  of  Paris  has  adopted  them,  after 
experiments,  for  disinfecting  sewers,  &c. ;  the  gas  companies  of  Paris,  and 
of  all  the  large  towns;  the  Transatlantic  Steamship  Company,  many  railway 
companies,  the  principal  mining  companies,  and  a  great  number  of  towns,  for 
use  in  the  fire  departments,  having  adopted  them  after  making  decisive  ex¬ 
periments. 

These  experiments  have  been  described  by  the  Counscil  d’Hygiene  et  de 
Salubritd  de  Paris,  by  the  Annales  des  Mines,  et  dcs  Ponts  et  Chaussdes,  the 
“  Moniteur,”  “  Constitutionnel,”  “  Presse,”  “  Mondes,”  and  all  the  journals  of 
the  cities  and  towns  in  which  experiments  with  this  invention  have  been  made. 

It  has  already  been  the  means  of  saving  nearly  one  hundred  lives,  and  the 
inventor  has  received  acknowledgments  of  its  merits  by  numerous  prizes  and 
medals  from  public  institutions.  It  is  perfectly  simple  in  its  use,  and  the  price 
is  so  low  as  to  place  one  or  more  within  the  reach  of  all  persons  having  property 
to  protect. 

The  “  Times,”  speaking  of  the  invention,  says, 

“A  very  interesting  and  successful  experiment  was  tried  in  Portsmouth 
Dockyard  by  M.  Galibert,  a  Frenchman,  the  inventor  of  an  apparatus  to  en¬ 
able  the  wearer  to  breathe  freely  in  the  midst  of  the  most  dense  smoke  arising 
from  a  fire.  Rear-Admiral  Wellesley,  Admiral  Superintendent  of  the  yard, 
the  Hon.  Captain  Egerton,  Captain  W.  Chamberlain, and  the  principal  officers 
of  the  dockyard  were  present  in  the  foundry,  the  drying-room  of  which  was 
appropriated  for  the  trial,  and  in  which  a  quantity  of  straw,  shavings,  oakum, 
&c.,  had  been  placed,  and  which  at  three  o’clock  was  ignited,  the  only  aperture 
(the  door)  being  then  closed,  so  that  the  place  was  soon  filled  with  a  dense 
volume  of  smoke.  M.  Galibert  then  produced  the  apparatus,  which  consisted 
of  a  canvas  bag,  fireproof,  which  he  inflated  with  air  by  a  small  pair  of  bellows ; 
two  gutta-percha  tubes  were  affixed,  at  the  end  of  which  was  a  mouthpiece, 
which  fitted  to  the  teeth,  the  nostrils  being  at  the  same  time  closed  by  a 
small  spring.  The  bag  was  then  slung  on  his  back.  Being  thus  prepared, 
he  entered  the  room,  the  door  closed  upon  him,  and  there  he  remained  eight 
minutes  and  fifty  seconds,  at  the  expiration  of  which  time  the  door  \\  as  opened, 
and  he  came  out  apparently  without  the  slightest  exhaustion  ;  after  which  one 
of  the  police  constables,  John  Lacy,  No.  1 57,  volunteered  to  try  the  experiment, 
which  the  admiral  permitted,  and  being  fully  equipped  and  instructed  by  the 
inventor,  he  entered  the  room,  where  he  remained  three  minutes  sufficiently 
long  to  test  the  utility  of  the  apparatus.  One  of  the  labourers  followed,  and 
remained  six  minutes,  and  both  men  stated  that  they  found  no  inconvenience 


638 


CHEMISTR  Y 


whi'e  in  —  they  could  breathe  as  freely  as  in  the  open  air,  and  could  have 
remained  any  length  of  time.  Subsequently  a  ladle  was  heated,  in  which  a 
quantity  of  sulphur  was  put,  thus  rendering  the  smoke  still  more  dense  ;  but 
M.  Galibert,  after  being  in  six  minutes,  returned  again  without  the  slightest 
nconvenience.  The  thermometer  was  at  910.” 

Carbonic  Oxide. 

Carbonic  Oxide  (symbol,  CO;  atomic  weight,  28).  —  When  carbonic  di¬ 
oxide  is  passed  through  red-hot  charcoal,  it  parts  with  one  atom  of  oxygen, 
which  unites  with  another  of  carbon  to  form  carbonic  oxide. 

CO*  +  C  =  2CO 

Carbonic  acid  Carbon.  =  Carbonic  oxide. 

This  gas  is  even  more  poisonous  and  insidious  than  carbonic  acid,  and  is 
produced  in  considerable  quantities  during  the  burning  of  bricks,  where  the 
conditions  are  favourable  for  the  passage  of  carbonic  acid  gas  through  red-hot 
charcoal  (the  cinders  called  “breeze”)  with  which  the  bricks  are  burnt. 

By  boiling  crystals  of  oxalic  acid  with  strong  sulphuric  acid,  the  former  is 
decomposed  into  carbonic  acid  and  carbonic  oxide  (CO*  and  CO),  the 
elements  (H20)  which  form  water  being  removed  by  the  sulphuric  acid. 

Carbonic  oxide  burns  with  a  lambent  blue  flame,  and  is  converted  into  car- 
la  mic  acid.  The  former  is  lighter  than  the  latter,  and  has  a  specific  gravity  of 
0967. 

Compounds  of  Carbon  with  Hydrogen. 

To  the  department  of  organic  chemistry  belongs  the  most  numerous  portion 
of  the  hydro-carbons.  There  are,  however,  two  compounds  of  carbon  and 
hydrogen  which  deserve  special  notice  here: 

Light  carburetted  hydrogen  (CH4) ;  Heavy  carburetted  hydrogen  (C2H4). 

Marsh  gas — firedamp — light  carburetted  hydrogen,  methyl  hydride  (CH,) 
— so  dangerous  in  coal-mines  because  the  gas  does  not  possess  any  odour  to 
warn  the  miner  of  its  presence — has  no  colour  or  taste,  and  is  evolved  from 
stagnant  pools  and  ditches  where  dead  leaves  accumulate  and  decompose. 

S.)da  and  sodium  acetate  heated  together  yield  sodium  carbonate  and  light 
carburetted  hydrogen  gas. 

Olefiant  gas  -heavy  carburetted  hydrogen,  ethylene  (C.H.) — is  an  important 
constituent  of  coal-gas,  to  which  it  imparts  its  chief  illuminating  powers.  Me¬ 
thyl  hydride  burns  with  a  bluish-yellow  flame,  whilst  olefiant  gas  burns  with  a 
luminous  and  somewhat  smoky  flame,  betraying  the  excess  of  carbon  it  con¬ 
tains  ;  in  fact,  this  gas  contains  twice  as  much  carbon  as  marsh  gas  united 
with  the  same  molecule  of  hydrogen.  It  is  prepared  by  carefully  heating  one 
part  of  alcohol  with  five  of  sulphuric  acid  :  the  elements  of  water  are  removed 
by  the  latter,  and  defiant  gas  (C2H4)  evolved.  It  is  called  olefiant  from  the 
Latin  oleum ,  oil,  and  to  make ;  because  the  associated  Dutch  chemists, 
Brandt,  Dieman,  Troostwick,  and  Laurenberg,  in  the  year  1796,  found  that 
when  it  was  mixed  with  chlorine  gas,  a  peculiar  liquid  resembling  a  heavy  oil 
was  produced. 

Both  of  these  hydro-carbon  gases  are  contained  in  coal-gas,  with  other  com¬ 
pounds  of  carbon,  and  various  impurities  which  it  is  the  duty  of  the  “  gas¬ 
works”  to  remove  before  the  gas  is  supplied  to  the  consumer.  But  the  con¬ 
sideration  of  such  an  important  theme  as  coal-gas  would  demand  more  space 
than  the  limits  of  this  work  will  permit. 


BORON. 


f>39 


BORON. 

Symbol,  B.  Atomic  weight,  io’Q. 


Sir  Humphrey  Davy  proved  this  to  be  an  element,  and  the  base  of  boracic 
acid,  in  the  year  1807.  Boracic  acid  is  obtained  from  borax,  so  called  from 
the  Arabic  buruk ,  which  signifies  brillia/it. 

Wohler  and  Deville  give  the  following  directions  for  the  preparation  of 
amorphous,  dull,  olive-green  boron  in  the  state  of  powder:  150  grammes  of 
fused  boracic  anhydride  (boracic  acid,  B203),  are  coarsely  powdered  and  mixed 
rapidly  with  90  grammes  of  sodium  cut  into  small  pieces.  The  mixture  is 
then  introduced  into  a  cast  iron  crucible  previously  heated  to  bright  redness; 
70  or  80  grammes  of  solid  and  previ¬ 
ously  fused  sodium  chloride  are  placed 
upon  the  top  of  the  mixture,  and  the 
crucible  is  covered.  As  soon  as  the 
reaction  is  over,  the  still  liquid  mass 
is  thoroughly  stirred  with  an  iron  rod, 
and  poured  whilst  red  hot  in  a  slender 
stream  into  a  large  and  deep  vessel 
containing  water  acidulated  with  hy¬ 
drochloric  acid.  The  pulverulent 
boron  is  then  collected  on  a  filter,  and 
washed  with  acidulated  water  till  the 
boracic  acid  is  got  rid  of;  after  which 
the  washing  may  be  continued  with 
pure  water  until  the  boron  begins  to 
run  through  the  filter.  It  is  finally 
dried  upon  a  porous  slab  without  the 
application  of  heat. 

Crystallized  Boron.  —  In  order  to 
convert  the  amorphous  into  the  crys¬ 
tallized  form,  the  same  chemists  adopt 
the  following  method : 

“A  small  Hessian  crucible  is  lined 
with  the  powder  or  amorphous  boron, 
made  into  a  paste  with  water,  the  bo¬ 
ron  being  pressed  in  strongly,  as  in 
the  ordinary  mode  of  lining  a  crucible 
with  charcoal.  In  the  central  cavity  a 
piece  of  aluminium,  weighing  from  6  to  9  grammes,  is  placed;  the  cover  is 
luted  on,  and  the  crucible  enclosed  in  a  second,  the  interval  between  the  two 
being  lined  with  recently  ignited  charcoal.  The  outer  crucible  is  next  closed 
with  a  luted  cover,  and  the  whole  exposed  for  a  couple  of  hours  to  a  heat  suffi¬ 
cient  to  melt  nickel;  the  temperature  is  then  allowed  to  fall,  and  when  cold 
the  contents  of  the  inner  crucible  are  digested  in  diluted  hydrochloric  acid, 
which  dissolves  out  the  aluminium ;  beautiful  crystals  of  boron  are  left,  gene¬ 
rally  transparent,  but  of  a  dark  brown  colour. 

A  quantity  of  scales  of  the  so-called  graphitoid  boron — an  alloy  of  boron 
with  aluminium  (B,A1)— are  formed  at  the  same  time  in  pale  copper-coloured 
opaque  plates. 


Fig.  490. 

Useful  Fur 71  ace forCruciblc  operations. 


640 


CHEMISTR  Y 


Fig.  491. — Strong  Fire-clay  Furnace. 


Boron,  like  carbon  and  silica,  exists  in  three  conditions,  viz.,  amorphous, 
crystalline,  and  graphitoidal.  Crystallized  boron  has  a  specific  gravity  of  2‘68, 
and  Deville  exhibited  crystals  of  the  octohedral  form  hard  enough  to  scratch 
the  ruby.  In  the  remarks  on  silicon  reference  will  be  made  to  the  manufacture 
of  artificial  precious  stones. 

The  most  important  com¬ 
pound  of  borcn  and  oxygen  is 
boracic  trioxide,  (boracic  acid, 
B_03.)  It  is  obtained  from  the 
volcanic  districts  of  Tuscany, 
which  puff  out  jets  of  steam 
and  gas:  thev  contain  small 
quantities  of  boracic  acid, 
and  are  condensed  and  dis¬ 
solved  in  the  small  lakes  and 
lagoons  surrounding  the  mouth 
of  the  jets.  The  very  weak 
solution  thus  naturally  formed 
would  involve  great  expense  for 
coal  or  other  fuel  if  evaporated 
in  the  ordinary  way;  but  Na¬ 
ture  gives  with  the  weak  solu¬ 
tion  of  boracic  acid  natural 
Fig.  492.  — Forge,  Bello-zus,  and  Iron  Tray ,  steam-jets,  and  these  are  used 

For  small  operations  where  an  intense  heat  is  required.  to  evapoiate  the  water  of  the 


SILICON. 


641 


lagoons.  From  borax  (Na2B407)  boracic  acid  is  procured  by  dissolving  four 
parts  of  pure  borax  in  boiling  water,  and  then  adding  sulphuric  acid  equivalent 
to  one-fourth  of  the  weight  of  the  borax.  Sodic  sulphate  is  formed,  and  bo- 


FlG.  493  . — Gas-burner ,  and  Platinum  Crucible  and  Crucible  Jacket , 

For  fusing  bodies  not  requiring  a  high  temperature. 


racic  acid  crystallizes  out  on  cooling  in  pearly-looking  scales:  these  are  washed 
with  ice-cold  water,  dried,  and  fused  in  a  platinum  crucible.  The  fused  crystals 
are  then  re-dissolved  in  four  times  their  weight  of  boiling  water,  and  the 
boracic  acid  crystallizes  on  cooling  in  a  state  of  purity. 


FlG.  494. — Dr.  Normandy's  Mixed  Air  and  Gas-burner , 

With  a  blowpipe  jet  in  centre  to  urge  dame  on  crucible. 

There  is  a  trifluoride  of  boron  (BFS)  and  a  boric  nitride  or  nitride  of  boron 
•BN),  for  boron  possesses  the  remarkable  property  of  combining  with  nitrogen 
at  a  red  heat. 


SILICON. 

Symbol,  Si.  Atomic  weight,  28. 

A  non-metallic  substance  (at  present),  whose  existence  in  flint  (si lex)  was 
suspected  by  Sir  H.  Davy,  silicon,  like  boron,  may  exist  without  form,  i.e., 
amorphous;  as,  for  instance,  when  obtained  by  passing  the  tetra-fluoride  of 

41 


642 


CHEMISTR  Y 


silica  into  water,  producing  an  acid  solution.  The  tetra-fluoride  is  obtained  by 
heating  a  mixture  of  sand  with  powdered  fluor  spar  and  sulphuric  acid.  The 
gas  must  be  passed  through  a  cup  containing  mercury,  or  the  deposited  silica 
hydrate  (H.OSiCb)  would  soon  close  the  tube,  and,  stopping  the  further  exit  ol 
the  gas,  would  cause  an  explosion  to  take  place. 

The  acid  liquor  neutralized  with  a  solution  of  caustic  potash  yields  potassic 
silica  fluoride  (2KF,  Si4F). 

When  this  salt  is  dried  and  mixed  with  nearly  its  own  weight  of  sodium, 
and  heated  in  a  glass  tube,  sodium  fluoride  is  formed,  whilst  silicon  is  reduced; 
and  when  the  whole  is  thoroughly  washed,  collected,  and  dried,  a  dull  brown 
powder  is  obtained. 

Silicon,  like  carbon  and  boron,  may  be  obtained  in  three  conditions — amor¬ 
phous,  graphitic,  and  crystalline.  In  the  amorphous  state  it  can  be  burnt  in 
oxygen,  and  then  forms  silica.  Crystals  of  silica  are  obtained  by  putting  into 
a  red-hot  crucible  a  mixture  of  three  parts  of  potassic  silica  fluoride  with  one 
of  metallic  sodium  and  four  of  zinc  :  of  course  the  perfection  of  manipulation 
requires  that  the  sodium  shall  be  minced  and  the  zinc  granulated.  When 
cool,  the  crystals  deposited  on  the  zinc  are  found  to  be  silica,  which  can  be 
separated  from  the  former  by  hydrochloric  acid,  and  subsequently  by  boiling 
nitric  acid.  Silica  thus  obtained  will  scratch  glass,  and  has  a  specific  gravity 
of  2-49. 

The  graphitic  form  of  silica  is  obtained  by  heating  the  amorphous  silica  at 
a  high  temperature. 

The  compound  of  oxygen  and  silica  which  specially  demands  consideration 
is  silicic  dioxide  or  silica — the  substance  which,  next  to  oxygen,  is  the  most 
abundant  in  nature.  It  not  only  exists  as  silicic  dioxide,  nearly  pure,  as  a 
mineral  (3iOa  =  6o),  but  is  abundantly  distributed  in  the  form  of  silicates 
through  the  mineral  productions  of  the  known  crust  of  our  globe.  Primary 
rocks  owe  their  hardness  chiefly  to  the  presence  of  silicic  dioxide. 

Silica  occurs  in  two  states — amorphous  when  prepared  by  passing  the  tetra- 
fluoride  of  silica  into  water,  as  already  described.  The  deposited  silica  may 
be  washed,  dried,  and  heated  to  a  great  heat,  and  then  appears  perfectly  snow- 
white. 

Common  flint  stones,  heated  red  hot  and  plunged  into  water,  afford  a  white 
powder  which  is  nearly  pure  silica.  Any  artificial  amorphous  form  of  silica  is 
easily  dissolved  in  alkaline  solvents,  hence  the  manufacture  of  water-glass. 

The  crystalline  forms  of  silica  quartz  are  legion.  “  Quartz  is  composed  of  pure 
silica,  generally  combined  with  minute  proportions  of  metallic  oxides,  from 
whence  the  varied  and  brilliant  colours  it  frequently  exhibits  are  derived.  It 
is  a  most  abundant  mineral,  forming  extensive  veins  and  masses  in  primitive 
and  transition  rocks,  and  consequently  is  diffused  over  almost  every  quarter 
of  the  globe.  It  is  an  essential  constituent  of  granite,  gneiss,  mica-slate,  and 
other  allied  rocks,  and  in  the  form  of  sand  forms  nearly  the  whole  of  the  mo¬ 
bile  soil  of  the  sterile  desert.  In  South  America  quartz  has  been  observed 
by  Humboldt  in  mountain  masses  or  beds,  many  hundred  feet  in  thickness. 
Its  specific  gravity  varies  from  2'5  to  2'8,  and  is  265  in  the  purer  varieties. 

“Quartz  consists  of  many  varieties,  differing  much  in  external  appearance,  all 
of  which  readily  scratch  glass,  and  equal  7  in  Prof.  Moh’s  scale  of  hardness. 
It  is  infusible  per  se  before  the  blowpipe,  but  with  soda  fuses  with  intumescence 
into  a  transparent  glass,  and  is  insoluble  in  all  acids  excepting  hydro-fluoric 
acid  :  when  pulverized  it  is  slightly  soluble  in  a  solution  of  caustic  potash. 


SILICON. 


64  3 


Quartz  occuis  massive  and  crystalline,  also  fibrous,  stalactite,  granular, 
form,  pseudo-morphous,  &c.”  *  ’ 


spongi- 


F IG.  495- — Single  Crystal  of  Quartz.  F IG.  496.— Group  of  Crystals  of  Quartz. 

The  following  are  the  names  used  bv  mineralogists  for  crystallized  quartz: 
Rock  crystal.  Dragon ite.  Quartz,  Phillips  Brook  and  Mi'ller,  &^c. ;  Quartz 
Many  A/aumaun,  Werner ,  Haiditiger ,  Hau smarm.  Rhombohedral  Quartz, 
Mob's.  VVhitestone  of  the  jewellers.  Berg  crystal. 

Siiica  .  .  9937 
Alumina  .  trace 


99 '37  Bucholz. 
Specific  gravity  2‘653  Bendant. 


Fig.  497. 

a.  F  rimary  form  of  crystal;  b,  the  usual  form,  hexagonal  prism,  terminated  by  hexagonal  pyramids. 

There  is  a  remarkable  combination  of  silicon  and  hydrogen  (H4Si)  called 
siliciuretted  hydrogen,  which,  like  phosphuretted  hydrogen,  takes  fire  spon- 


*  “Elementary  Treatise  op  Quartz  and  Opal.”  By  S  W.  Traill,  F  G.3. 


41 — 2 


644 


CHEMISTR  V 


taneously  in  the  air,  forming  silica  and  water.  A  silicic  nitride,  sulphide, 
chloride,  and  fluoride  are  also  amongst  the  carefully  recorded  compounds  of 
silica. 

The  “Literary  and  National  Gazette”  thus  describes  the  manufactuie  of 
gems,  and  the  colouring  and  improving  of  stones  belonging  to  the  quartz  class. 

How  Gems  are  Manufactured. 

“That  many  things  glitter  which  are  not  gold  is  well  known;  but  do  the 
wearers  of  jewellery  know  that  the  bright  and  beautiful  colours  exhibited  by 
most  of  their  much-prized  gems  are  purely  artificial?  Nature  supplies  the 
raw  material,  and  art  steps  in  to  embellish  it.  The  brilliant  necklace  or 
bracelet,  which,  with  the  native  hue  of  the  stone,  would  by  no  means  be  con¬ 
sidered  ornamental,  becomes  matchless  in  tint  and  lustre  after  passing  through* 
the  hands  of  the  artificer.  Your  chemist,  always  discovering  something  and 
always  ready  with  marvellous  transformations,  is  truly  a  remarkable  personage. 
He  is  jealous  of  his  secrets,  but  not  always  able  to  keep  them.  If  he  could 
set  a  seal  on  his  doings,  our  readers  would  not  have  been  entertained  with  the 
present  article,  in  which  we  shall  take  leave  to  reveal  some  of  his  processes. 

“  Let  us  begin  with  agate — rather  a  common  stone,  found  almost  everywhere, 
and  in  numerous  varieties,  among  which  are  the  chalcedony,  cornelian,  onyx, 
sardonyx,  and  heliotrope.  They  all  consist  principally  of  quartz,  and  are 
more  or  less  pellucid.  In  some  places  they  are  surprisingly  abundant.  One 
of  these  places  is  Oberstein,  some  thirty  or  forty  miles  up  the  valley  of  the 
Nahe,  a  region  not  often  visited  by  summer  tourists,  yet  interesting  enough  to 
repay  him  who  shall  explore  its  devious  byways  and  paths  along  the  river. 
At  the  village  just  mentioned,  and  at  I  dal,  four  miles  distant,  formations  of 
coarse  red  conglomerate  are  met  with,  interposed  with  trap  and  greenstone; 
and  in  soft  strata  in  these  rocks  agates  are  found  in  considerable  quantities. 
The  workings  may,  indeed,  be  called  agate-quarries,  for  they  are  carried  on  in 
the  precipitous  side  of  a  hill;  and  to  him  who  sees  them  for  the  first  time 
there  is  something  remarkable  in  the  species  of  industry  created  by  the  pre¬ 
sence  of  the  stones. 

“  The  nodules  of  agate,  as  they  come  from  their  long-undisturbed  bed,  are 
generally  of  an  ashen-grey  colour.  The  first  operation  in  the  process  of  trans¬ 
formation  is  to  wash  them  perfectly  clean  ;  then  to  put  them  into  a  vessel  con¬ 
taining  a  mixture  of  honey  and  water,  which,  being  closely  covered,  is  plunged 
into  hot  ashes  for  two  or  three  weeks.  The  essential  thing  is  to  keep  the  liquid 
from  boiling,  but  at  a  high  temperature.  After  a  sufficient  interval  the  stones 
are  taken  out,  cleansed,  passed  through  a  bath  of  sulphuric  acid,  and  then 
they  undergo  a  second  course  of  roasting  in  the  hot  ashes. 

“  To  produce  a  colour  in  the  stones,  it  is  necessary  they  should  be  penetrated 
by  some  carbonizable  substance.  This  is  effected  by  the  honey,  which,  under 
the  influence  of  long-continued  heat,  finds  its  way  into  the  interior  of  the 
crystal,  where  its  carbonization,  if  not  complete  in  the  first  instance,  is  finished 
by  the  sulphuric  acid.  Some  lapidaries  use  olive  oil  instead  of  honey.  The 
shade  of  colour  depends  on  the  porosity  of  the  layers  of  the  stone :  the  most 
porous  become  at  times  perfectly  black.  Some  are  coloured  in  two  or  three 
hours,  others  in  as  many  days,  others  in  a  week  or  two,  and  some  resist  all 
attempts  to  change  their  natural  hue.  Some,  when  they  are  taken  out  of  the 
pan,  are  found  to  be  a  rich  dark  brown,  or  chocolate;  others,  again,  having 


MANUFACTURE  OF  GEMS.  645 


been  penetrated  by  the  colouring  matter  between  the  layers,  arc  striped  alter¬ 
nately  white,  grey,  and  brown,  like  the  onyx  and  sardonyx. 

“  By  soaking  the  stones  in  a  solution  of  sulphate  of  iron,  and  then  placing 
them  for  a  few  hours  in  the  oven,  a  fine  cornelian  red  is  produced  in  the  porous 
layers,  while  those  not  porous  remain  unaltered.  Thus  it  not  unfrequently 
happens  that  very  coarse  and  common  stones — muddy  yellow  or  cloudy  grey 
—  which  in  their  natural  condition  would  be  valueless,  are  passed  off  as  stones 
of  the  first  quality.  It  is  only  within  the  last  forty  years  that  this  process  has 
been  known  in  Germany;  but  the  Italian  lapidaries  were  acquainted  with  it 
centuries  ago.  Hence  we  can  account  for  the  exquisite  colour  of  antique  cameos 
and  other  ornaments  once  numerous  in  the  cabinets  of  Italy,  and  now  to  be  seen 
in  museums  and  private  collections  in  all  parts  of  the  world. 

“The  dealers,  when  making  their  purchases  of  what  we  may  call  the  raw 
material,  select  what  appears  to  be  a  desirable  piece,  and  chipping  off  a  minute 
portion,  they  moisten  the  exposed  surface  with  the  tongue,  and  watch  the  ab¬ 
sorption  of  the  moisture.  If  regular  and  equal,  the  stone  is  good  for  an  onyx; 
if  not,  it  is  added  to  the  heap  of  inferior  varieties.  This,  however,  is  but  a 
rough-and-ready  test,  and  not  always  decisive. 

“The  pores  of  the  stones  by  which  the  colour  is  conveyed  and  retained 
are  visible  with  the  microscope,  and  the  effect  of  various  tints  is  produced 
according  as  the  light  falls  upon  them  at  different  angles.  The  rainbow  agate 
is  full  of  minute  cells,  which,  when  exposed  to  the  sun,  produce  prismatic 
colours,  as  is  observed  of  the  striae  of  mother-of-pearl.  To  detect  cavities  in 
the  stones,  they  are  soaked  in  water,  which,  slowly  penetrating,  reveals  the 
hollows.  Some  already  contain  water  when  first  found  ;  and  it  is  a  remarkable 
fact  that,  if  kept  in  a  dry  place,  the  water  disappears,  but  without  leaving  the 
slightest  traces  of  moisture  on  the  surface,  and  the  stones  can  only  be  refilled 
by  boiling  them. 

“  Balls  of  striped  red  chalcedony  are  much  prized  :  a  large  one  weighing 
100  lb.  was  found  in  1844  near  Weisselberg,  and  was  sold  in  the  rough  for 
700  guelders.  Some  kinds  of  chalcedony  are  made  to  appear  of  a  citron 
yellow,  by  a  two  days’  roasting  in  an  oven,  and  a  subsequent  immersion  in  a 
close  hot  bath  of  spirits  of  salt  for  two  or  three  weeks.  A  blue  colour, 
which  has  all  the  effect  of  a  torquoise,  is  also  produced,  but  the  particular 
colouring  process  has  hitherto  been  kept  a  secret.  1  hese  stones  which  are 
naturally  coloured  are  at  times  roasted,  to  heighten  the  tint  and  add  to  its 
permanency.  The  Brazilian  cornelian  becomes  singularly  lustrous  under  the 
process ;  the  explanation  being  that  the  long-continued  action  of  heat  removes 
the  oxhydrate  of  iron  contained  in  the  stone,  leaving  it  with  a  clear  brightness 
diffused  through  the  whole  mass.  The  smallest  stones  are  roasted  before 
polishing,  but  the  large  ones,  of  which  saucers,  vases,  cups,  plates,  &c.,  are 
made,  are  first  cut  into  the  required  shape  and  thinness — otherwise  they  fly  to 
pieces  when  exposed  to  heat.  After  all  the  colouring  operations  have  been 
gone  through,  the  stones  are  ground  on  awheel  soaked  in  oil  fora  day,  to  con¬ 
ceal  the  fine  scratches  and  give  a  good  polish,  and  then  cleaned  oft  with  bran. 

“Those  who  examined  the  collection  of  gems  and  works  ot  ait  from  rare 
stones  in  the  Great  Exhibition  of  1851,  "  ill  remember  the  elegant  onyx  vases 
of  different  colours  —  some  streaked  with  white  natural  veins;  the  cups  of  red 
chalcedony;  a  chain  of  the  same  substance  in  large  square  links  of  different 
colours  and  without  visible  joints  ;  besides  other  objects  so  beautifully  finished 
that  a  prize  medal  was  awarded  to  the  manufacturers. 


646 


CHEMISTR  V 


“  So  far  we  have  been  treating  of  methods  by  which  Art  assists  Nature:  we 
come  now  to  the  gems  that  are  not  found  in  the  side  of  a  quarry,  but  formed 
in  the  chemist’s  laboratory.  Before  the  days  of  Berlin  wool  and  crochet-work, 
young  ladies  used  to  amuse  themselves  by  making  crystalline  baskets  and 
trays,  as  ornaments  for  the  mantelpiece;  but  they  had  first  to  dissolve  their 
alum.  The  chemist  works  by  oiner  means,  and,  especially  since  the  applica¬ 
tion  of  electro-galvanism  to  his  processes,  there  is  something  really  wonderful 
in  the  results.  He  produces  crystals  at  pleasure,  and  in  lumps  that  would 
astonish  those  who  once  laboured  so  hard  in  search  of  the  Philosopher’s  Stone. 
A  few  years  ago  M.  Ebelmas  laid  before  the  French  Academy  of  Sciences 
specimens  of  artificial  quartz — some  white,  others  blue,  red,  and  violet;  and 
by  mixing  chloride  of  gold  with  the  silicic  acid  used  in  the  composition,  he 
produced  a  mass  traversed  throughout  with  delicate  veins  of  gold,  similar  to 
the  lumps  brought  from  Australia  and  California.  By  a  modification  of  his 
process  he  produced  hydrophane— that  species  of  opal  which  is  transparent 
only  when  immersed  in  water — and  specimens  also  of  the  allied  crystal,  hyalite. 
In  this  operation  silicic  ether  and  moist  air  are  principally  employed;  and  a 
variety  of  colours  could  be  imparted  by  the  admixture  of  different  coloured 
alcoholic  solutions.  Chloride  of  gold  produces  a  beautiful  topaz  yellow ;  and 
by  exposing  the  crystal  for  a  time  to  light,  the  gold  is  dispersed  through  it  in 
flakes,  as  an  aventurine ;  and  kept  in  sunlight,  the  flakes  change  to  a  violet  or 
rose-colour,  and  become  transparent.  In  this  fact  we  have  an  extraordinary 
instance  of  molecular  action — the  distribution  of  metallic  scales  through  a 
solid  mass;  one  which,  as  some  geologists  suppose,  helps  to  throw  light  on 
the  mode  of  formation  of  rocks  and  minerals.  That  pieces  of  wood,  plants, 
and  animal  substances  will  become  silicified,  or,  as  is  commonly  said,  petrified, 
is  well  known  ;  and  though  often  wondered  at,  the  diffusion  of  the  gold  flakes 
through  the  crystal  is  yet  more  marvellous.” 

Everybody  has  seen  and  knows  the  nature  of  that  very  common  form  of 
silicon  called  “sand,”  with  which  vast  areas  are  covered  and  called  deserts. 
The  mechanical  properties  of  sand  are  amusing,  but  its  application  for  cutting 
purposes  is  most  valuable,  and  ha.,  formed  the  subject  of  a  patent  by  B.  C. 
Tilghman,  of  Philadelphia,  Pennsylvania,  and  called 

The  Sand-Blast  Process  for  Cutting  Hard  Substances. 

In  this  process,  a  stream  of  sand  is  introduced  into  a  rapid  jet  of  steam  or 
air  so  as  to  acquire  a  high  velocity,  and  is  then  directed  upon  any  hard  or 
brittle  substance  so  as  to  cut  or  wear  away  its  surface. 

For  work,  such  as  cutting  or  ornamenting  stone,  where  a  considerable  quan¬ 
tity  of  material  is  to  be  removed,  a  steam  jet  of  from  60  to  120  lbs.  pressure 
has  generally  been  used  as  the  propelling  agent.  The  sand  is  introduced  by 
a  central  tube  of  about  J  inch  bore,  and  the  steam  issues  from  an  annular 
passage  surrounding  the  sand  tube.  The  impetus  of  the  steam  then  drives 
the  sand  through  a  chilled  iron  tube  §  inch  bore,  and  about  6  inches  long, 
imparting  velocity  to  it  in  the  passage,  and  the  sand  finally  strikes  upon  the 
stone,  which  is  held  about  1  inch  distant  when  a  deep  narrow  cut  is  desired, 
but  may  be  10  or  15  inches  distant  when  a  broad  surface  is  to  be  operated  on. 

This  chilled  iron  tube  is  the  only  part  of  the  apparatus  which  is  worn  away 
by  the  cutting  action  of  the  sand  ;  it  is  so  arranged  as  to  be  easily  replaced, 
and  lasts  about  ten  hours. 


MANUFACTURE  OF  GEMS. 


647 


To  produce  ornaments  or  inscriptions  on  stone,  either  in  relief  or  intaglio, 
a  stencil  of  iron  or  caoutchouc  is  held  or  cemented  to  the  stone,  and  the  sand- 
jet  is  moved  with  an  even  and  steady  motion  over  the  whole  surface,  so  that 
all  the  exposed  parts  may  be  ait  to  the  same  depth 

The  skill  and  time  of  the  artist  may  be  devoted  exclusively  to  making  the 
stencil ;  this  being  prepared,  the  most  elaborate  and  intricate  designs  can  be 
cut  as  rapidly  as  the  most  simple.  A  stencil  of  cast  iron  inch  thick  will 
serve  to  make  too  cuts  y'g  inch  deep  in  marble,  and  will  be  worn  down  to 
about  -[V  inch  thickness.  Malleable  iron  stencils  last  about  four  times  as 
long  as  cast  iron. 

The  durability  of  caoutchouc  as  compared  with  stone,  under  these  circum¬ 
stances,  is  remarkable.  A  stencil  made  of  a  sheet  of  vulcanized  caoutchouc 
about  ^  thick,  exposed  to  sand  driven  by  50  lbs.  steam  at  2  feet  distance, 
has  lasted  with  scarcely  perceptible  wear,  while  50 cuts  were  made  in  marble, 
each  cut  being  about  ^  inch  deep,  or  about  I2|  inches  in  all,  or  200  times  the 
thickness  of  the  caoutchouc.  With  a  supply  of  steam  equal  to  about  horse¬ 
power,  at  a  pressure  of  about  100  lbs.,  the  cutting  effect  per  minute  was  about 
1 5  cubic  inches  of  granite,  or  4  cubic  inches  of  marble,  or  10  cubic  inches  of 
rather  soft  sandstone.  To  cut  a  face  or  level  surface  on  a  rough  stone,  the 
sand-jet  is  made  to  cut  a  groove  about  1  inch  deep  along  the  whole  length  of 
the  stone,  the  overhanging  edge  is  then  broken  off  with  the  hammer,  and  the 
jet  is  advanced  an  inch  and  a  new  groove  is  cut,  and  its  overhanging  edge  is 
broken  off,  and  so  on.  To  cut  a  deep  channel,  as  in  quarrying,  two  jets  are 
used,  making  parallel  grooves  about  3  inches  apait,  leaving  between  them  a 
narrow  fin  or  tongue  of  stone,  which  is  broken  off  by  a  tool,  and  the  jets  are 
advanced  and  new  grooves  cut.  The  jets  are  set  at  divergent  angles,  so  that 
the  sides  of  the  channel  are  parallel,  and  it  is  made  wide  enough  to  admit  the 
whole  jet  pipe  to  enter  to  any  desired  depth. 

When  effects  of  a  more  delicate  nature  are  desired,  and  only  small  quanti¬ 
ties  of  material  are  to  be  removed,  the  blast  of  air  lrom  an  ordinary  rotary  fan 
is  used  as  the  propelling  medium. 

Sand  driven  by  an  air-blast  of  the  pressure  of  4  inches  of  water  will  com¬ 
pletely  grind  or  de-polish  the  surface  of  the  glass  in  ten  seconds. 

If  the  glass  is  covered  by  a  stencil  of  paper  or  lace,  or  by  a  design  drawn 
in  any  tough  elastic  substance,  such  as  half-dried  oil,  paint,  or  gum,  a  picture 
will  be  engraved  on  the  surface. 

Photographic  copies  in  bichromated  gelatine,  from  delicate  line  engravings, 
have  been  thus  faithfully  reproduced  on  glass. 

In  photographic  pictures  in  gelatine,  taken  from  nature,  the  lights  and 
shadows  produce  films  of  gelatine  of  different  degrees  of  thickness.  A  care¬ 
fully  regulated  sand-bl  1  st  will  act  upon  the  glass  beneath  these  films  more  or 
less  powerfully  in  proportion  to  the  thickness  of  the  films,  and  the  half-tones 
or  gradations  of  light  and  shade  are  thus  produced  on  the  glass. 

If  we  apply  the  sand-blast  to  a  cake  of  resin  on  which  a  picture  has  been 
produced  by  photography  in  gelatine,  or  drawn  by  hand  in  oil  or  gum,  the  bare 
parts  of  the  surface  may  be  cut  away  to  any  desired  depth.  The  lines  left  in 
relief  will  be  well  supported,  their  base  being  broader  than  their  top,  and 
there  being  no  under-cutting,  as  is  apt  to  occur  in  etching  on  metal  with 
acid. 

An  electrotype  from  this  matrix  can  be  printed  from  in  an  ordinary  press. 

The  sand-blast  has  been  applied  to  cutting  ornaments  in  wood,  cleaning 


64B 


CHEMISTRY. 


metals  from  sand,  scale,  &c  ,  cleaning  the  fronts  of  buildings,  graining  or 
frosting  metals,  cutting  and  dressing  millstones,  and  a  variety  of  other 
purposes 

The  technical  use  of  sand  is  further  extended  by  converting  it  into  ordinary 
glass,  and  also  into  a  peculiar  silicate,  represented  according  to  Miller  by  the 
formula —Na.,0, 4Si02,  called  “soluble  glass,”  which  is  prepared  by  melt¬ 
ing  together  8  parts  of  dried  carbonate  of  soda,  or  io  of  carbonate  of  potash, 
with  15  parts  of  pure  sand  and  1  part  of  charcoal.  The  charcoal,  by  its  ten¬ 
dency  to  form  carbonic  oxide  at  the  expense  of  the  oxygen  of  the  carbonate, 
facilitates  the  decomposition  of  this  salt ;  a  black  glass  is  thus  obtained,  which 
is  not  soluble  in  cold  water,  but  is  almost  completely  dissolved  by  five  or  six 
times  its  weight  of  boiling  water.  According  to  Fuchs  it  is  this  soluble  glass 
which  is  employed  in  fixing  fresco  colours  by  the  process  known  as  “  Stereo- 
chromy.”  The  ground  used  in  this  process  for  the  reception  of  the  colour  con¬ 
sists  of  a  mixture  of  lime  and  fine  sand,  cemented  by  a  solution  of  soluble 
glass.  The  colours  ground  up  with  water  are  then  applied,  and  a  varnish  of 
soluble  glass  is  brushed  over  the  whole. 

The  material  best  adapted  to  this  purpose  consists  of  a  mixture  of  this 
soluble  glass  solution  with  about  one-fifth  of  its  bulk  of  a  solution  of  the 
monosilicate,  both  solutions  being  in  a  concentrated  state. 

Mr.  Ransome  has  applied  solutions  of  “  soluble  glass  ”  to  prevent  the  decay 
of  magnesian  or  other  limestones  which  are  exposed  to  the  weather  ;  and  he 
prepares  a  very  hard  artificial  sandstone  by  mixing  sand  with  a  solution  of 
calcic  chloride,  pressing  it  into  a  mould,  and  then  decomposing  the  lime  salt 
by  “  soluble  glass  ”  forced  in  by  pressure.  The  salt  formed  is  washed  out, 
and  the  insoluble  hard  silicate  remains. 


SELENIUM. 

Symbol,  Sc.  Atomic  weight,  7 9'5. 

This  element  is  intimately  connected  with,  and  allied  to,  sulphur,  and  was 
discovered  by  Berzelius,  in  1817,  in  the  refuse  of  a  sulphuric  acid  manufactory 
at  Gripsholm,  near  Fahlun,  in  Sweden.  It  has  been  found  m  the  natural 
state  at  Culebras,  in  Mexico. 

The  vitreous  form  of  the  element,  obtained  by  melting  this  substance,  is 
well  shown  in  the  medallion  portraits  of  Berzelius,  which  used  formerly  to  be 
very  common,  and  are  cast  in  selenium  (Fig.  498).  When  selenium  is  dis¬ 
solved  in  carbonic  disulphide  and  deposited  from  this  solution,  it  assumes  the 
crystalline  form.  There  is  evidently  a  change  in  density  when  selenium  is 
crystallized,  because  the  element  in  the  fused  or  vitreous  state  has  a  specific 
gravity  of  4-500,  and  4700  in  the  crystalline  form ;  moreover,  the  latter  melts 
at  a  temperature  of  2170  F.,  whilst  the  former  softens  at  a  heat  a  little  above 
the  boiling-point  of  water.  Dr.  Miller  says  the  statements  regarding  the  point 
of  fusion  of  selenium  are  discordant,  owing  to  its  power  of  existing,  like  sulphur, 
in  several  distinct  modifications.  It  has  neither  taste  nor  smell,  and  when 
examined  by  transmitted  light,  in  a  finely-divided  state,  has  a  red  colour. 

Fused  selenium  forms  a  solid  of  a  deep  brown  colour,  with  a  glassy  fracture 


SULPHUR . 


649 


and  metallic  lustre.  It  is  insoluble  in  water,  and  is  a  non-conductor  of  heat 
and  electricity.  It  burns  in  the  air  with  a  bright  blue  flame,  emitting  a  pecu¬ 
liar  odour. 


FlG.  498 .—Portrait  of  Berzelius ,  the  Discoverer  of  Selenium. 

(From  a  cast  in  that  substance  ) 


The  compounds  of  oxygen  and  selenium  are  selenic  dioxide,  or  selenious 
anhydride  (SeO*),  selenic  trioxide  (SeOs), — the  latter  has  not  yet  been  isolated, 
although  the  acid  and  salts  corresponding  with  it  are  known,— selenic  acid,  or 
dihydric  selenate  (H2Se04).  There  are  consequently  selemtes  and  se  eniates. 

Seleniuretted  hydrogen,  or  dihydric  selenide  (H2Sc),  is  prepaied  by  t  ic 
action  of  an  acid  on  a  selenide,  and  gas  is  obtained  which  painfully  stimulates 
the  nose,  destroying  for  some  hours  the  sense  of  smell;  indeed,  a  very  small 
bubble  of  the  gas'  let  into  the  nostrils  of  the  operator  deprives  him,  says 
Griffiths,  so  completely  of  the  sense  of  smell,  that  he  cannot  discover  even  the 
extremely  pungent  odour  of  ammonaical  gas.  This  compound  corresponds 
in  its  properties  with  that  nauseous-smelling  gas  called  sulphuretted  hydiogen. 

There  are  two  compounds  of  selenium  and  chlorine,  Se2U2  and  beU,;  the 
former  is  a  brown  volatile  fluid,  and  the  latter  a  volatile  white  crystalline 


mass. 


SULPHUR. 

Symbol,  S.  Atomic  weight,  32. 

The  greater  quantity  of  sulphur  used  in  England  comes  from  [he jojcamc 
regions  of  Sicily,  near  the  base  of  Mount  Ftna,  am  11  P  <  , 

borders  of  the  Mediterranean.  The  native  sulphur  is  pur 
and  the  apparatus  employed  is  shown  at  Fig.  499 >  a  b 

“TnTsis  a  manufacturer  named  Michel,  of  Marseilles  devisrf  an  ^pamtns 
which  with  some  slight  modification,  is  in  use  up  to  the  present  clay.  rig. 
499  represents  the  retort  wherein  the  sulphur  is  converted  mtovagur,  and  a 

condensing-chamber  into  which  this  *5  con'or  1  r  beneath  which  is  a 
apparatus,  as  in  the  drawing,  consists  first  o  a  re  ,  reservoir  n 

furnace,  A:  this  retort  is  filled  with  liquid  sulphur  from  the  reservoir,  n, 


65° 


CHEMISTR  Y. 


wherein  the  crude  sulphur  is  melted  by  the  waste  heat  of  the  furnace  to  faci¬ 
litate  its  introduction  into  the  retort.  When  the  retort  has  become  sufficiently 
hot,  the  sulphur  begins  to  pass  as  vapour  through  the  tube  or  opening  D  into 
the  conclensing-chamber,  E.  This  chamber  is  built  entirely  of  brick,  with  a 
well-cemented  brick  floor.  On  its  upper  part  a  small  chimney  is  erected  ;  this 
chimney  contains  a  small  wooden  valve  or  door,  capable  of  opening  outwards 
to  allow  the  expanded  air  to  escape,  and,  in  case  of  explosion,  to  allow  the 
gases  produced  immediate  exit.  This  apparatus,  when  cold,  allows  solid  sul¬ 
phur  to  form  at  once  in  the  shape  of  the  ordinary  commercial  flowers  of 
sulphur ;  the  vapours  immediately  coming  in  contact  with  the  cold  chambers 


Fig.  499.— 77/ c  Subliming  Apparatus  used  in  the  purification  of  crude 

Sulphur. 

are  chilled,  and  fall  as  a  minutely-divided  solid.  These  flowers,  as  they  are 
called,  are  removed  before  the  chamber  gets  hot,  which  is  the  case  after  a  few 
days’  working.  The  whole  of  the  heat  which  the  sulphur  has  taken  up  in  order 
to  become  vapour  being  given  out  to  the  walls,  they  thus  acquire  such  a  high 
temperature  as  to  fuse  sulphur;  therefore  it  can  no  longer  become  solid,  but 
condenses  on  their  surface  in  a  liquid  form,  and  falls  down  to  the  bottom,  where 
it  collects.  When  the  operator  is  satisfied  that  sufficient  has  distilled  over,  he 
proceeds  to  remove  it ;  this  he  does  by  the  plug  apparatus,  F,  which  is  only  an 
iron  plug  with  a  long  handle,  and  by  pushing  the  plug  inwards  he  opens  the 
passage  for  the  flow  of  liquid  sulphur,  which  runs  into  suitable  moulds  to  form 
the  sticks  or  rolls  of  commerce.  The  residue  is  raked  out  of  the  retort,  which 


SULPHUR. 


65 1 


is  immediately  charged  again  by  removing  the  plug  that  closes  the  tube  be¬ 
tween  the  vessel  B  and  the  retort.” 

Native  sulphur  occurs  in  the  amorphous  and  crystalline  states.  When  pure, 
sulphur  is  insoluble  in  water,  tasteless,  but  emits  a  peculiar  odour.  It  is  very 
inflammable,  and  takes  fire  at  a  temperature  between  450°  and  500°  F.,  pro¬ 
ducing  the  pungent  and  very  suffocating  gas  called  sulphurous  anhydride  (S02). 

Although  chiefly  used  in  the  manufacture  of  oil  of  vitriol,  sulphur  is  em¬ 
ployed  extensively  in  the  manufacture  of  lucifer  matches,  and  is  an  important 
constituent  of  gunpowder.  It  is  also  used  for  bleaching  silk,  flannel,  feathers,  &c. 

There  are  three  modifications  of  sulphur  :  first,  the  natural  crystals,  the 
octohedron  with  a  rhombic  base,  and  two  other  allotropic  conditions,  viz.,  one 
ootained  by  melting  and  crystallizing  sulphur  in  needles,  and  the  third  a  red 
amorphous  substance,  obtained  by  pouring  melted  sulphur  into  water. 

The  compounds  of  sulphur  with  oxygen  are  two  in  number: 


Sulphurous  anhydride  . 
Sulphuric  anhydride 

The  oxyacids  of  sulphur  are  very  numerous: 
Sulphurous  acid 
Sulphuric  acid 
Hyposulphurous  acid 
Dithionic  acid 
Trithionic  acid 
Tetrathionic  acid  . 

Pentathionic  acid  . 


.  SO,—  64. 
SO,=  80. 

.  H,SO,=  82. 
.  H2SOt—  98. 
H2S2H204— 132. 
.  H2S2Oa=  162. 
.  H2SjO„=  194. 
.  H2S4Ofi=226. 
.  H*SjO«— 258. 


Sulphurous  anhydride,  or  sulphuric  dioxide  (symbol  S02,  atomic  weight  64), 
are  the  scientific  names  of  the  pungent  suffocating  fumes  given  off  when  sulphur 
is  burnt.  It  is  easily  prepared  by  boiling  2  oz.  of  quicksilver  with  3  oz.  of 
sulphuric  acid;  the  former  deprives  the  latter  of  a  portion  of  its  oxygen.  The 
reaction  that  takes  place  is  shown  in  the  following  equation: 

Hg  +  2H,SO*  =  HgSO,  +  SO,  4-  2ll20 

Mercury.  Oil  ot  vitriol  =  Sulphate  of  Sulphurous  Water. 

mercury.  anhydride. 

Copper  may  be  used  instead  of  mercury,  but  when  a  small  quantity  of  sul¬ 
phurous  anhydride  is  required,  the  evolution  of  the  gas  is  much  quicker  with 
the  latter  metal. 

Sulphurous  dioxide  has  a  specific  gravity  of  2-247,  and  therefore  is  easily 
collected  by  displacement  or  over  mercury  in  the  mercurial  trough.  I  he  gas 
should  be  washed  by  allowing  it  to  bubble  through  a  little  water  placed  in  a 
Woolfe’s  bottle. 

Sulphurous  dioxide  has  no  colour,  and  cannot  lie  respired.  When  subjected 
to  a  temperature  of  — io°  F.,  by  means  of  a  freezing  mixture  of  snow  and  salt, 
it  is  reduced  to  the  liquid  state’ at  the  ordinary  pressure  of  the  air. 

After  collecting  the  liquid  gas  in  a  strong  tube,  the  latter  may  be  hermeti¬ 
cally  sealed,  and  when  the  temperature  rises  to  6o°  F .  the  liquefied  gas  exerts 
a  pressure  of  more  than  2I  atmospheres,  viz.,  2  54. 

The  liquid  gas  cooled  below  — 105°  F.  freezes  to  a  crystalline  solid. 

Sulphurous  anhydride  combines  with  water,  and  is  then  termed  sulphurous 
acid  H,SO  .  Water  dissolves  68  8  times  its  bulk  of  sulphurous  anhydride  at 
a  temperature  of  320  F.  The  solution  is  used  now  for  certain  throat  diseases 
in  the  form  of  fine  spray,  and  is  a  great  boon  to  public  singers  or  speakers. 


652 


CHEMISTRY. 


and  in  some  cases  the  cure  effected  is  almost  magical  in  rapidity.  The  acid 
is  a  powerful  antiseptic  and  anti-putrescent  body.  It  stops  the  ordinary  fer¬ 
mentation  of  sugar,  and  is  one  of  the  best  disinfectants  that  can  be  used. 
Sulphur  burnt  in  the  air  will  afford  sulphurous  anhydride  sufficiently  good  for 
this  purpose.  Unlike  chlorine,  it  is  used  as  a  deoxidizing  agent  for  bleaching 
silk,  flannel,  isinglass,  feathers,  sponge,  straw,  &c.  Sulphurous  anhydride  is 
not  an  inflammable  gas,  and  will  not  support  the  combustion  of  a  burning 
taper. 

Sulphuric  acid  (dihydric  sulphate,  H2S04  =  98)  is  the  most  important  acid 
used  in  commercial  chemical  processes.  One  hundred  thousand  tons  are  made 
and  used  annually  in  this  country. 

The  chief  importance  of  the  gas  already  considered,  viz.,  sulphurous  anhy¬ 
dride,  is  due  to  the  fact  that  it  is  the  starting-point  in  the  manufacture  of  oil 
of  vitriol.  The  gas,  by  a  most  ingenious  process,  is  made  to  combine  with 
half  as  much  oxygen  again  as  it  already  contained  ;  and,  what  is  still  cleverer, 
the  oxygen  is  obtained  for  nothing,  because  it  is  taken  from  the  great  reservoir 
of  oxygen,  viz.,  the  air.  Sulphurous  anhydride  and  oxygen,  both  dry,  when 
passed  over  spongy  platinum  heated  in  a  tube,  combine,  and  sulphuric  anhy¬ 
dride  (SO;,)  is  produced.  It  is  called  by  some  authors  sulphuric  trioxide. 
Curious  to  state,  this  body  does  not  redden  litmus  or  blacken  the  skin.  It 
combines  with  water  with  great  rapidity,  and,  when  brought  in  contact  with 
the  latter  fluid,  hisses  like  a  red-hot  iron,  forming  sulphuric  acid,  H2SOv 

In  the  commercial  process  sulphurous  anhydride  (S02)  is  oxidized  in  a 
capacious  leaden  chamber  by  the  intervention  of  another  gas  (nitric  oxide), 
with  the  assistance  of  moist  air.  Nitric  oxide  in  contact  with  the  air  produces 
the  red  fumes  of  nitric  trioxide  (N2Oa)  which  yields  oxygen  to  the  sulphurous 
anhydride,  and  converts  it  into  sulphuric  acid.  The  decomposition  is  thus 
tersely  described  by  Roscoe: 

“  S0i  +  H,0  +  N203=H2S04-j-N202 — sulphuric  dioxide,  water,  and  nitric 
trioxide — yield  sulphuric  acid  and  nitric  oxide.  The  nitric  oxide  formed  in 
this  decomposition  takes  up  another  atom  of  oxygen  from  the  air ,  becoming 
N203,  and  this  is  again  able  to  convert  a  second  molecule  of  S02  with  H20 
into  H2S04,  being  a  second  time  reduced  to  N.O.,,  and  ready  again  to  take  up 
another  atom  of  oxygen  from  the  air.  Hence  it  is  clear  that  N202  acts  simply 
as  a  carrier  of  oxygen  between  the  air  and  S02;  an  indefinitely  small  quantity 
of  this  nitric  trioxide  being,  therefore,  theoretically  able  to  convert  an  inde¬ 
finitely  large  quantity  of  sulphurous  dioxide,  water,  and  oxygen  into  sulphuric 
acid.” 

Protohydrate  of  sulphuric  acid  (the  oil  of  vitriol  of  commerce),  H2SO„,  is  a 
dense  oily-looking  fluid,  having  a  specific  gravity  of  i'842.  It  blackens  organic 
matter,  and  when  mixed  with  water  becomes  very  hot :  the  volume  of  acid 
and  water  is  found  to  be  reduced  in  bulk  when  cold. 

Sulphuric  acid  boils  at  a  temperature  of  620°  F.,  emitting  a  dense  white 
vapour,  and  it  distils  without  decomposition.  Some  pieces  of  platinum  foil 
should  be  placed  in  the  bottom  of  a  distilling  vessel  to  prevent  the  violent  and 
explosive  formation  of  the  acid  vapour. 

If  a  little  sulphuric  acid  is  placed  in  a  beaker  up  to  a  certain  mark,  it  will 
be  found  in  the  course  of  a  day  or  so  to  have  risen  above  the  mark,  in  conse¬ 
quence  of  the  absorption  of  the  watery  vapour  contained  in  the  air.  Organic 
substance,  and  especially  sugar,  is  completely  decomposed  and  charred  when 
oil  of  vitriol  is  poured  upon  it.  This  acid  has  little  or  no  action  on  metals  in 


SULPHUR. 


653 


the  cold  state,  but  when  some  of  the  latter  are  boiled  in  sulphuric  acid,  sul¬ 
phates  are  obtained. 

In  the  practice  of  the  art  of  photography  (see  p.  574),  large  quantities  of 
sodium  hyposulphate  are  used.  The  latter  salt  is  obtained  by  passing  a  current 
of  sulphuric  dioxide  into  a  solution  of  sodium  sulphide;  the  resulting  hypo- 
sulphide  is  purified  by  crystallization.  Hyposulphurous  acid,  or  dithionous  acid 
(H2S*H*04=  132),  forms  with  sodium  a  salt  in  which  one  of  the  molecules  of 
hydrogen  is  replaced  by  that  of  sodium,  viz.,  Na,H  S20,.  A  solution  of  this 
salt  possesses  the  property  of  dissolving  out  the  silver  compound  (iodide  or 
chloride,  as  the  case  may  be)  which  remains  unaltered  by  light;  whilst  those 
portions  of  the  silver  compounds  reduced  to  the  metallic  state  by  the  action 
of  light  are  not  affected  by  this  salt,  which  is  therefore  said  to  fix  the  photo¬ 
graphic  picture.  Hyposulphurous  acid  is  only  known  in  combination,  and 
has  not  yet  been  isolated. 

Compounds  of  Sulphur  with  Hydrogen. 

Hydrosulphuric  acid ;  sulphuretted  hydrogen;  dihydric  sulphide,  H3S  =  34. 
This  gas  was  discovered  by  Scheele  in  the  year  1774,  and  it  is  usually  obtained 
from  ferrous  sulphide  (FeS)  by  the  action  of  dilute  sulphuric  acid. 

To  prepare  the  ferrous  sulphide,  some  clean  iron  turnings  or  small  coils  of 
iron  wire  are  to  be  placed  in  a  covered  crucible  banked  up  with  hot  coke  on 
the  stage  of  the  forge  bellows  (p.  588).  The  blast  should  then  be  urged  until 
the  crucible  has  attained  a  bright  red  heat,  when  the  cover  of  the  crucible  may 
be  raised,  and  fragments  of  sulphur  dropped  in.  The  action  is  very  apparent, 
as  the  iron  glows  with  a  still  more  intense  heat  in  the  act  of  combining  with 
the  sulphur,  and  if  the  operation  is  nicely  performed,  the  whole  assumes  the 
liquid  state,  and  may  be  poured  into  a  mould  or  allowed  to  cool  in  the  crucible. 

Ferrous  sulphide,  by  decomposition  with  sulphuric  acid,  yields  sulphuretted 
hydrogen;  the  iron  being  displaced  from  the  sulphur  by  the  hydrogen. 

FeS  +  H*SOt  =  H*S  +  F*SOt 

Ferrous  Sulphuric  Sulphuretted  Ferrous 

sulphide.  acid.  hydrogen.  sulphate 

The  sulphide  of  iron  is  placed  in  the  bottle  A,  and  sufficient  water  is  poured 
upon  it  through  the  funnel  B.  A  little  sul¬ 
phuric  acid  is  now  added,  and  the  gas  passes 
through  the  tube  C,  connected  with  E  by  a 
piece  of  vulcanized  india-rubber  tube.  Here 
the  gas  is  absorbed  by  distilled  water  in  F, 
and  if  required  pure,  again  escapes,  when 
the  latter  is  saturated  through  G  by  11  anti  j 
into  the  beaker  glass,  K.  containing  more 
distilled  water,  or  any  fluid,  such  as  a  solu¬ 
tion  of  lead  or  arsenic,  whose  presence  it 
may  be  desirable  to  determine. 

Water  at  59°  F.  dissolves  3  23  times  its 
bulk  of  sulphuretted  hydrogen.  The  solution 
has  a  slight  acid  reaction,  and,  of  course, 
the  smell  of  the  gas,  which  reminds  the  nose 
of  the  odour  of  putrid  eggs.  This  gas,  which 
consists  of  two  volumes  of  hvdrogen  and  one 


654 


CHEMISTR  Y 


volume  of  sulphur  vapour  condensed  into  two  volumes,  has  a  specific  gravity 
of  ri9i  ;  and  too  cubic  in.  weigh,  at  6o°  F.  and  30  in.  bar.,  38  grains.  It  is 
very  poisonous,  and  if  one  measure  is  mixed  with  600  or  1 ,200  measures  of  air, 
the  highly  diluted  gas  is  still  most  poisonous  and  will  soon  cause  the  death  of 
a  mouse  or  a  bird. 

The  analytical  chemist  requires  this  gas  for  the  purpose  of  determining  in 
a  qualitative  analysis  the  particular  group  to  which  any  metal  discoverable  by 
this  gas  may  be  referred,  and  it  is  one  of  the  most  useful  re-agents  employed 
in  the  laboratory. 

There  is  another  compound  of  sulphur  and  hydrogen  called  hydric  per¬ 
sulphide,  or  persulphide  of  hydrogen,  H2S2. 

Sulphur  also  unites  with  carbon,  forming  a  most  useful  and  volatile  fluid 
called  carbonic  bisulphide  or  bisulphide  of  carbon,  CS2=76.  This  compound 
dissolves  phosphorus  in  the  ordinary  state,  but  not  when  in  the  amorphous 
condition.  It  is  one  of  the  best  solvents  of  caoutchouc,  gums,  sulphur,  &c. 

Sulphur  chloride  (S2C12  =  135),  sulphur  dichloride  (SCI2=  103),  and  nitrogen 
sulphide  (SN)  complete  the  list  of  sulphur  compounds. 


PHOSPHORUS. 

Symbol,  P.  Atomic  weight,  3r. 

A  merchant  of  Hamburg,  engaged  in  the  useless  attempt  to  obtain  the 
Philosopher’s  Stone  exactly  200  years  ago,  viz.,  in  the  year  1669,  discovered 
accidentally  this  peculiar  substance.  The  name  of  this  clever  and  perse¬ 
vering  chemist  was  Brandt,  who  described  the  phosphorus  he  obtained  as  a 
“  dark,  unctuous,  daubing  mass.”  There  are  many  other  interesting  particulars 
respecting  the  history  of  the  discovery  of  this  substance  that  will  be  found 
in  a  most  exhaustive  pamphlet  by  Mr.  George  Gore,*  from  which  the  following 
is  taken : 

“  In  a  ‘  Historical  Sketch  of  the  Progress  of  Pharmacy  in  Great  Britain,  by 
Jacob  Bell,’  it  is  stated,  that  ‘A  house  and  shop,  with  a  laboratory,  were  built 
on  the  Bedford  estate,  in  the  year  1706,  by  Ambrose  Godfrey  Hanckwitz,  who 
had  carried  on  business  as  a  chemist  in  the  neighbourhood  since  1680.  He 
was  a  maker  of  phosphorus  and  other  chemicals,  which  were  rare  at  that  period, 
and  which  he  sold  in  different  parts  of  the  country  during  his  travels.  His 
laboratory  was  a  fashionable  resort  in  the  afternoon  on  certain  occasions,  when 
he  performed  popular  experiments  for  the  amusement  of  his  friends.  It  opened 
with  glass  doors  into  a  garden,  which  extended  as  far  as  the  Strand,  but  which 
is  now  built  upon.  Four  curious  old  prints  of  the  laboratory  in  its  former  state 
are  in  the  possession  of  its  present  proprietors,  Messrs.  Godfrey  and  Cooke, 
of  Southampton  Street,  Covent  Garden,  also  a  portrait  of  Ambrose  Godfrey 
Hanckwitz,  engraved  by  George  Vertue  (1718),  which  he  had  distributed 
among  his  customers  as  a  keepsake.’ 

“When  we  consider  that  1,000  parts  of  urine  contain  scarcely  one  part  of 
phosphorus,  and  of  this  probably  only  a  portion  was  obtainable  by  the  processes 
first  in  use,  we  shall  not  be  surprised  at  the  statement  of  Boyle  that  ‘  the  liquor 
yields  but  a  small  proportion  of  the  desired  quintessence,’  or  at  the  price  of  5 os. 


*  “On  the  Origin  and  Progress  of  the  Phosphorus  and  Match  Manufactures  ”  By  G.  Gore. 


PHOSPHORUS. 


655 


an  ounce  charged  by  Hanckwitz  for  his  product.  Even  an  improved  process, 
purchased  and  published  by  the  French  Government  in  1737,  yielded,  under 
the  direction  of  Hellot,  Geoffroi,  Dufay,  and  Duhamel,  only  four  ounces  of 
phosphorus  for  every  five  hogsheads  of  the  liquid. 

After  the  death  of  Hanckwitz,  in  1741,  some  experiments  were  made  by 
Margraaf,  Fourcroy,  Vauquelin,  and  others;  but  no  great  improvement  in  the 
production  of  phosphorus  appears  to  have  been  effected  until  1769,  when  Gahn 
made  the  important  discovery  of  phosphoric  acid  in  bones.  Margraaf  had 
already  demonstrated  the  individuality  of  this  acid  as  early  as  the  year  1740, 
and  it  only  now  remained  to  devise  a  process  for  extracting  it.  Scheele  imme¬ 
diately  did  this,  and  various  eminent  d  emists  quickly  succeeded  in  making 
various  improvements  in  the  method  of  working,  and  bequeathed  unto  us  sub¬ 
stantially  the  same  process  of  manufacture  as  that  now  in  operation. 

“  The  present  sources  of  phosphorus  are  the  bones  of  buffaloes  and  other 
animals,  slaughtered  in  the  great  hunting-grounds  of  South  America  (the 
Pampas  bordering  the  La  Plata),  where  bones  are  used  as  fuel ;  exhausted 
‘  bone-black,’  or  ‘  animal  charcoal  ’  of  sugar  refineries  ;  calcareous  deposits  of 
phosphate  of  lime,  or  ‘  mineral  guano  ’  from  the  coast  of  Yucatan  ;  and  similar 
depos  ts  from  the  island  of  Sombrero ;  but  the  chief  of  these  sources  is  the 
burnt  bones  from  Monte  Video,  Rio  Janeiro,  Rio  Grande,  &c.,  and  the  animal 
charcoal  of  the  sugar  refineries.  These  various  substances  contain  from  60  to 
90  per  cent,  of  their  weight  of  phosphate  of  lime,  or  fiom  12  to  18  per  cent,  of 
phosphorus. 

“The  phosphorus-yielding  material,  of  whatever  kind,  having  been  suitably 
ground,  a  weighed  quantity  of  the  powder  is  placed  in  a  large  circular  tub,  lined 
with  lead,  with  a  mixture  of  oil  of  vitriol  and  water,  and  stirred  by  means  of  a 
revolving  wooden  stirrer,  driven  by  a  steam-engine,  steam  being  admitted  by 
a  pipe  into  the  mixture  to  facilitate  the  action  of  the  sulphuric  acid  upon  the 
powder. 

“  The  changes  which  bone-ash  or  other  varieties  of  phosphate  of  lime  undergo 
in  the  above  operation  are  these:  the  oil  of  vitriol  or  sulphuric  acid  gradually 
unites  with  the  lime  and  forms  sulphate  of  lime,  and  sets  the  phosphoric  acid 
free;  so  that  after  the  process  there  remains  a  semi-fluid  mixture  of  a  solid 
substance,  sulphate  of  lime  (gypsum  or  plaster  of  Paris),  with  a  fluid  body, 
phosphoric  acid,  separable  by  filtration. 

“  The  creamy  mixture  is  now  transferred,  by  means  of  ladles,  to  a  filter  or 
drainer,  from  which,  with  the  aid  of  occasional  stirring,  the  phosphoric  acid 
filters  into  a  vessel  beneath.  Water  is  added  to  the  drained  contents  of  the 
filtei  until  the  drainings  cease  to  taste  acid.  1  he  sulphate  of  lime  or  gypsum 
is  then  removed  in  its  damp  state,  to  a  furnace  or  other  source  of  heat,  and 
dried,  and  constitutes  a  residuary  product  suitable  for  the  manufacture  of  arti¬ 
ficial  manures. 

“The  dilute  filtered  solution  of  phosphoric  acid,  containing  some  phosphate 
of  lime  and  a  small  quantity  of  sulphate  of  lime  dissolved  in  it,  is  transferred 
to  leaden  vessels  and  slowly  evaporated  over  a  gentle  fire ;  the  small  quantity 
of  gypsum  then  deposits  itself  upon  the  bottoms  of  these  vessels,  and  is  removed 
by  scraping.  The  liquid  is  deprived  of  as  much  more  of  its  water  as  possible 
by  further  evaporation  in  similar  vessels,  and  on  cooling  acquires  the  con¬ 
sistence  of  cocoa-nut  butter. 

“  The  butter-like  paste  is  then  well  mixed  with  a  due  proportion  of  powdered 
charcoal,  and  the  mixture  heated  in  furnaces  of  brick  or  iron  until  it  is  brought 


6  56 


CHEMISTR  Y. 


into  as  dry  a  powder  as  can  be  attained.  The  powder  consists  of  charcoa’, 
phosphoric  acid  (a  compound  of  phosphorus  and  oxygen),  a  little  phosphate 
of  lime,  and  a  little  water,  which  is  chemically  combined  with  the  phosphoric 
acid,  and  not  capable  of  removal  by  the  means  yet  applied. 

“We  have  already  alluded  to  the  intense  heat  employed  by  Boyle  and 
Hanckwitz  in  their  distillation  of  phosphorus:  the  same  is  also  necessary  in 
the  present  mode  of  manufacture.  The  vessels  in  which  the  phosphorus  is 
separated  consist  of  a  number  (about  ten)  of  small  retorts,  of  a  convenient 
shape,  carefully  constructed  of  the  most  refractory  fire-clay,  narrowed  at  their 
mouths,  and  arranged  nearly  close  together  in  a  horizontal  row  in  a  furnace, 
somewhat  similar  to  the  retorts  in  a  gas-works.  They  are  placed  in  a  nearly 
horizontal  position,  with  their  open  ends  slightly  raised,  and  in  a  furnace  so 
constructed  as  to  subject  them  to  nearly  a  white  heat. 

“The  black  powder  is  introduced  into  the  retorts  when  the  latter  are  com¬ 
paratively  cool,  and  the  retorts  are  about  half  filled  with  the  mixture.  Bent 
pipes,  open  at  both  ends,  are  inserted,  air-tight  by  means  of  clay,  into  the 
mouths  of  the  retorts,  and  their  outer  ends  dip  into  warm  water,  in  cast-iron 
basins,  placed  to  receive  the  distilled  phosphorus.  1  may  now  incidentally 
remark  that  all  the  manipulations  with  ordinary  phosphorus  in  its  simple  and 
separated  state  are  performed  under  the  surface  of  water,  otherwise  it  would 
quickly  inflame  and  be  reconverted  into  phosphoric  acid. 

“  The  heat  ol  the  furnace  is  gradually  raised,  and  in  the  course  of  some  hours 
phosphorus  begins  to  distil  over,  and  accumulates  in  a  melted  state  in  the 
basins  of  water.  The  fire  is  still  further  raised,  by  gradual  means,  until  a  most 
intense  heat  is  obtained;  the  phosphorus  then  distils  rapidly.  The  heat,  after 
being  thus  continued  as  long  as  any  more  phosphorus  appears,  is  gradually 
decreased,  and  the  basins  containing  the  crude  phosphorus  are  removed.  The 
time  occupied  in  the  distillation  is,  in  some  cases,  protracted  from  forty-eight 
to  seventy-two  hours. 

“  In  this  operation  the  charcoal,  at  a  high  temperature,  combines  with  the 
oxygen  of  the  phosphoric  acid,  forming  therewith  carbonic  oxide  and  carbonic 
acid  gases,  which  escape  through  the  nose-pipe,  and  the  phosphorus  thus  set 
free  is  conveited  into  vapour  by  the  heat,  and  distils  over  into  the  receiving- 
basins.  At  the  same  time,  the  portion  of  water  not  extracted  by  the  preceding 
process  is  also  decomposed,  and,  its  hydrogen  set  free,  combines  with  some  of 
the  phosphorus  and  forms  phosphuretted  hydrogen  gas.  The  inflammable 
gases,  carbonic  oxide  and  phosphuretted  hydrogen,  are  conducted  away  from 
the  phosphorus  basins  by  means  of  a  pipe,  and  consumed. 

“  When  the  distillation  is  at  an  end,  the  furnace  is  cooled  down  and  the  resi¬ 
duary  contents  of  the  retorts  extracted.  The  residue  consists  chiefly  of  char¬ 
coal  (of  which  there  is  always  an  excess)  and  of  undecomposed  phosphate  of 
lime,  together  with  a  few  impurities,  and  is  used  in  the  composition  of  manures, 
the  phosphorus  in  it  being  of  too  difficult  or  too  unprofitable  extraction.  From 
the  penetrating  and  destructive  character  of  phosphorus,  the  retorts  require 
frequent  renewing,  some  manufacturers,  when  the  best  fire-clay  is  not  employed, 
not  using  them  for  more  than  one  operation. 

“  The  appearance  of  a  phosphorus  distillery  containing  between  200  and  300 
retorts,  which  we  have  frequently  visited  when  in  full  operation  and  the  furnaces 
at  their  maximum  heat,  is  somewhat  fearful:  the  long,  yellow  flames  of  phos¬ 
phuretted  hydrogen  and  carbonic  oxide  shooting  forth  from  the  escape-pipes ; 
bits  of  burning  phosphorus  spitting  forth  in  fiery  balls  from  little  crevices  or 


PHOSPHORUS. 


657 


’eaks  at  the  mouths  of  the  retorts ;  the  incessant  bubbling  of  the  vapour  of 
phosphorus  and  escaping  gases  in  the  basins  of  hot  water ;  the  almost  unbear¬ 
able  heat  from  the  furnaces  on  each  side,  and  from  the  red-hot  flues  under 
foot;  the  intolerable  stench  of  phosphuretted  hydrogen  and  burning  phos¬ 
phorus  ;  together  with  the  acid  fumes  and  filthy  grim  aspect  of  the  place, 
combined  to  produce  an  impression  on  our  senses  which  we  cannot  fail  to 
remember. 

“  The  small  cakes  of  crude  phosphorus,  each  weighing  several  pounds,  are 
collected  from  the  iron  receiving-basins  when  cold,  and  melted  together  under' 
water.  The  impurities  which  were  carried  over  from  the  retorts  into  the  basins 
by  the  current  of  gases  and  phosphorus  vapour,  now  settle  to  the  bottom  of 
the.  fluid  mass,  and  the  supernatant  phosphorus  is  drawn  over  into  shallow 
copper  pans,  containing  a  small  quantity  of  hot  water  to  prevent  contact  of 
air,  by  means  of  leaden  syphons  previously  filled  with  hot  water,  and  allowed 
to  solidify. 

“The  large  cakes  or  cheeses  of  phosphorus  thus  obtained  still  contain 
impurities,  and  are  of  a  dirty  red  colour,  chiefly  arising  from  the  mechanical 
admixture  of  a  red  variety  of  phosphorus  in  small  particles.  They  are  broken 
to  pieces  under  cold  water,  and  the  fragments  placed  in  hot  water  contained 
in  a  leaden  vessel  (heated  by  steam),  together  with  a  bleaching  agent.  The 
phosphorus  is  stirred  with  the  heated  mixture  until  it  is  bleached,  or  its 
brownish  colour  is  removed,  which  generally  occupies  two  or  three  hours. 

“  The  liquid  phosphorus  is  again  drawn  by  means  of  syphons  into  shallow 
copper  pans,  and  allowed  to  solidify.  It  is  then  broken  under  water,  and  the 
pieces  are  placed  in  hot  water  in  a  double-sided  (or  steam-jacketed)  vertical 
iron  cylinder,  lined  with  lead,  with  a  perforated  bottom  covered  with  chamois 
leather  and  canvas;  and  while  in  the  fluid  state  pressure  is  applied  to  the 
phosphorus,  and  it  passes  through  the  leather,  &c.,  into  a  vessel  of  hot  water 
beneath,  leaving  the  residuary  impurities,  red  phosphorus,  &c.,  upon  the  cloth 
in  the  form  of  a  dirty  reddish  substance  of  an  earthy  appearance. 

“The  bleached  and  purified  phosphorus  is  now  cast  into  wedge-shaped 
pieces,  or  it  is  moulded  into  cylindrical  sticks,  half  an  inch  in  diameter,  and 
io  in.  long,  by  the  aid  of  glass  tubes  immersed  into  the  phosphorus  under 
water,  or  by  means  of  an  apparatus  with  tubes  specially  contrived  for  the  pur¬ 
pose.  On  some  occasions  the  phosphorus  is  very  brittle  and  difficult  to  draw 
into  sticks,  but  if  it  is  in  a  satisfactorily  pure  state  it  is  as  ductile  as  lead  or 
soft  copper  wire.  The  appearance  of  the  purified  phosphorus  in  the  form  of 
wedges  is  that  of  very  transparent  wax  or  glass  of  a  slightly  greenish -yellow 
colour,  but  when  in  the  form  of  sticks  it  usually  appears  colourless.  It  is 
needful  on  all  occasions  to  protect  the  purified  substance  from  strong  daylight, 
otherwise  it  soon  becomes  yellow  and  opaque,  f  or  conveyance  it  is  always 
packed  in  water,  generally  in  tin  cans,  the  covers  of  which  are  soldered  air- 

tight.  . 

“  The  phosphorus  we  have  described  is  that  of  the  ordinary  kind  ;  but  there 
is  another  variety,  equally  pure,  discovered  in  1848  by  Professor  Schrotter.  ot 
Vienna,  which  is  produced  as  follows:  The  ordinary  phosphorus  in  its  purihed 
state  is  placed  under  water  in  a  cast-iron  boiler  over  a  furnace;  then  melted, 
cooled,  and  the  water  removed  from  its  surface.  I  he  vessel  is  then  immediate!) 
and  securely  closed,  air-tight  (except  a  small  iron  tube  for  the  escape  of  vapour  , 
by  a  cast-iron  cover.  The  lid  has  a  vertical  iron  tube,  closed  at  its  lower  end, 
fixed  in  it,  which  projects  downwards  into  the  phosphorus,  and  is  open  at  its 

42 


658 


CHEMISTR  V. 


upper  end  for  the  reception  of  a  thermometer.  Heat  is  now  gradually  applied 
by  means  of  the  furnace  until  the  phosphorus  is  at  about  450°  F.,  and  that 
temperature  is  maintained  for  a  greater  or  less  period  of  time,  according  to  the 
amount  of  phosphorus  operated  upon,  and  the  mass  is  then  allowed  to  cool. 
A  quantity  of  about  200  pounds  is  kept  heated  about  three  or  four  weeks.  After 
this  process  the  vessel  is  opened,  and  the  phosphorus,  which  has  now  become 
a  hard,  red  brick-like  substance,  is  covered  with  water,  and  extracted  by  means 
of  iron  bars,  &c.  This  process  of  conversion  requires  to  be  conducted  with 
great  circumspection,  otherwise  (from  overheating  of  the  phosphorus)  fearful 
explosions  may  ensue;  experience  has,  however,  shown  that  they  may  be 
almost  wholly  avoided. 

“  For  commercial  purposes  the  red  or  amorphous  phosphorus,  as  it  is  termed, 
is  required  to  be  in  a  state  of  fine  powder ;  the  stony  fragments  are,  therefore, 
broken  into  small  pieces  under  water  in  a  mortar,  and  ground  under  water 
between  pieces  of  mill-stone  in  a  vessel  supplied  with  a  small  stream  of  water, 
which  carries  off  the  finer  particles  in  its  overflow  stream  into  a  large  tank, 
where  they  gradually  subside,  or  into  a  filter  where  they  are  collected.  A  pro¬ 
cess  is  then  resorted  to  for  the  separation  of  any  ordinary  phosphorus  which 
the  powder  may  contain. 

“  This  wet  and  finely-divided  substance  having  been  dried,  sifted,  and  packed 
in  air-tight  tins,  is  ready  for  sale. 

“  It  is  well  known  in  modern  chemistry  that  a  substance  may  exist  in  two 
or  more  physical  states,  possessing  very  different  physical  and  chemical  pro¬ 
perties,  and  that  there  may  be  as  great  a  difference  in  the  properties  of  the 
same  substance  in  its  different  states  of  aggregation  as  there  is  between  two 
chemically  different  substances.  For  instance,  there  is  as  great  an  amount  of 
physical  difference  between  carbon  as  it  exists  in  the  diamond  and  as  it  exists 
in  pure  lamp-black  as  between  copper  and  silver  or  silver  and  gold.  The  two 
kinds  of  phosphorus  we  have  described  are,  then,  precisely  the  same  chemical 
substance,  but  in  different  states  of  aggregation.  The  following  is  a  comparison 
of  their  properties.  We  will,  for  convenience,  term  them  white  and  red  phos¬ 
phorus  : 


WHITE, 

Poisonous. 

Evolves  a  strong  odour. 
Phosphorescent  —  luminous  in  the 
dark. 

Melts  at  1080  F. 

Very  transparent. 

Almost  colourless. 

Freely  soluble  in  various  liquids. 

Distinctly  crystalline. 

Soft,  may  be  indented  by  the  nail. 
Flexible  as  copper  or  lead. 


RED. 

Innocuous. 

Nearly  odourless. 

Not  phosphorescent — perfectly  Alu¬ 
minous. 

Melts  at  above  500°  F. 

Opaque. 

Varies  in  colour  from  nearly  black 
(with  metallic  lustre)  to  iron-grey, 
brick-red,  crimson,  and  scarlet. 

Nearly  insoluble  in  all  liquids. 

Destitute  of  all  crystalline  structure 
(amorphous). 

Hard  as  a  common  red  brick. 

Brittle  as  glass. 


“The  great  and  most  conspicuous  fact  is  that  red  phosphorus  may  be  kept 
in  the  dry  state,  exposed  to  the  air,  without  inflaming;  whilst  the  ordinary 
variety,  under  the  same  circumstances,  quickly  ignites.  The  minutest  quantity 


PHOSPHORUS. 


659 


of  ordinary  phosphorus  in  the  red  or  amorphous  variety  can  be  detected  by 
digesting  the  latter,  in  the  state  of  powder,  in  bisulphide  of  carbon,  and  then 
letting  fall  a  single  drop  of  the  clear  liquid  upon  a  saucer  floating  upon  boiling 
water  in  a  dark  place;  luminosity  will  immediately  appear  if  white  phosphorus 
is  present. 

“  There  are  several  uses  to  which  phosphorus  has  been  applied  ;  but,  as  far 
as  quantity  is  concerned,  almost  the  only  important  application  is  in  the  manu¬ 
facture  of  lucifer  matches.  It  is  remarkable  that,  although  the  property  of 
phosphorus  of  igniting  by  friction  was  known  soon  after  its  discovery,  it  was 
not  until  about  the  year  1833  that  it  was  successfully  applied  to  the  manufacture 
of  matches.  It  was  then  sold  wholesale  at  four  guineas  a  pound;  in  1837,  at 
two  guineas;  and  at  the  present  time,  at  less  than  2 s.  6 d.  Manufactories 
of  it  exist  in  Great  Britain,  France  (Lyons),  Bavaria,  Baden,  Austria,  and 
Sardinia. 

“  Since  the  commencement  of  the  manufacture  of  phosphorus  upon  a  large 
scale  in  England,  in  1845,  the  value  of  phosphorus  imported  into  this  country 
has  regularly  and  rapidly  decreased.  According  to  the  reports  of  the  Great 
Exhibition  of  1851,  the  value  of  phosphorus  imported  from  all  parts  into  Great 
Britain  in  1844  was  ,£2,567,  and  in  1850  only  ^3.  And  since  that  period  it  has 
become  an  article  of  constant  export  to  the  Continent  and  other  parts,  the 
proportion  consumed  in  the  United  Kingdom  being  comparatively  small.  In 
his  ‘Catechism  of  Agricultural  Chemistry/  Professor  Johnston  states  that 
200,000  lbs.  of  phosphorus  are  consumed  in  London  alone  per  annum.  Persons 
conversant  with  the  actual  consumption  know  that  at  that  time,  and  probably 
at  the  present  hour,  it  would  not  exceed  20,000  lbs. 

“  It  is  also  stated  in  a  recent  publication  on  Chemistry,  by  Professor  Mus- 
pratt  (article  ‘  Phosphorus,’  p.  680),  that  phosphorus  ‘  is  prepared  as  an  article 
of  manufacture  in  large  quantities  in  London  and  Paris.  Kane  has  calculated 
that  in  the  latter  city  alone  about  200,000  lbs.  are  yearly  produced.’  There 
may  have  been  once  a  very  small  production  in  London  and  Paris,  but  it  has 
long  since  entirely  ceased.  The  enormous  consumption  of  fuel  necessitates 
that,  for  an  economic  production,  the  manufactory  be  placed  where  coal  is 
cheaply  obtained  ;  and  the  quantity  of  phosphorus  produced  in  all  France,  at 
the  date  of  Dr.  Kane’s  book,  is  not  likely  to  have  been  at  all  more  than  20,000 
lbs.  It  is  plain  that,  by  mistake,  a  cypher  too  many  has  been  added.’ 

Red  Phosphorus. 

Dr.  Muspratt  describes  the  following  process  for  preparing  this  form  of 
phosphorus,  which  is  effected  in  the  apparatus  shown  in  I*  lg.  501.  A  quantity 
of  common  dried  phosphorus  is  placed  in  the  flask  A,  to  the  neck  ol  which  a 
long  narrow  tube,  b,  bent  downwards,  is  attached,  the  open  end  of  which  dips 
into  a  little  mercury.  The  removal  of  the  air  is  accomplished  by  means  ol  a 
current  of  carbonic  acid  evolved  from  the  bottle  E,  containing  marble  and 
hydrochloric  acid.  The  gas  is  dried  by  passing  it  over  chloride  ol  calcium 
contained  in  the  tube  F.  The  flask  being  emptied  of  air,  the  tube  is  closed  by 
fusion  at  the  narrow  portion,  a ,  and  the  apparatus  evolving  carbonic  acid  re¬ 
moved.  The  flask  is  then  heated  by  means  of  an  oil  bath,  c ;  the  phosphorus 
melts  readily,  and  by  regulating  the  heat  steadily  between  450°  and  460°  by 
means  of  a  thermometer,  /,  and  maintaining  it  thirty  or  forty  hours,  nearly  the 
whole  will  be  converted  into  the  solid  amorphous  variety’.  \N  hen  the  meta- 

42 — 2 


66o 


CHEMISTR  Y 


morphosis  appears  to  be  complete,  the  apparatus  is  allowed  to  cool.  Any 
unaltered  phosphorus  is  separated  by  digestion  in  bisulphide  of  carbon,  in  which 
amorphous  phosphorus  is  insoluble.  The  latter  is  afterwards  collected  in  a 
filter  and  washed  with  bisulphide  of  carbon,  as  long  as  anything  is  removed 
from  it,  which  may  be  ascertained  by  evaporating  a  small  portion  in  a  watch- 
glass,  when  any  dissolved  phosphorus  will  remain  behind. 


Fig.  501. 


Crystals  of  phosphorus  having  a  bright  metallic  lustre  and  a  specific  gravity 
of  2'34 — nearly  double  that  of  ordinary  phosphorus,  which  has  a  specific  gra¬ 
vity  of  rS3 — may  be  obtained  by  dissolving  amorphous  or  red  phosphorus  in 
melted  lead.  Amorphous  phosphorus  has  a  specific  gravity  of  2' 14. 

There  are  two  oxides  of  phosphorus  which  are  anhydrous,  viz. — 

Phosphoric  trioxide  (phosphorus  anhydride),  P203; 

Phosphoric  pentoxide  (phosphoric  anhydride),  P205; 

The  latter  represents  the  dense  white  smoke  that  passes  off  when  phosphorus 
is  burnt  in  a  cup,  so  that  the  air  does  not  have  free  access  to  it ;  or  if  phos¬ 
phorus  is  burnt  under  a  bell-jar  in  dry  air,  a  quantity  of  a  snow-white  floc- 
'culent  non-crystalline  substance  collects  on  the  sides  of  the  glass,  or  falls 
chiefly  to  the  lower  part  if  the  glass  is  standing  on  a  marble  disc.  This  sub¬ 
stance  is  phosphoric  pentoxide,  and,  like  sulphuric  trioxide,  hisses  like  a  red- 
hot  iron  when  brought  in  contact  with  water.  The  equation  is  P2Oi  +  3H20, 
the  phosphoric  pentoxide  having  united  with  three  molecules  of  water  to  form 
2H3P04,  two  molecules  of  tribasic  phosphoric  acid.  There  are  two  other  acids 
of  phosphorus,— dibasic  and  monobasic;  the  hydrogen  being  the  base,  as 
already  explained,  that  determines  the  rank  of  the  acid. 


PHOSPHORUS. 


66 1 


1.  Monobasic  hypophosphorous  acid  .  .  HPH,0,; 

2.  Dibasic  phosphorous  acid  .  .  .  H2PH03; 

3.  Tribasic  phosphoric  acid  ....  H3PO  . 

As  there  are  three  allotropic  conditions  of  phosphorus,  so  there  are  three 
varieties  of  phosphoric  acid — in  fact,  different  acids: 

Tribasic  phosphoric  acid,  HsP04; 

Pyrophosphoric  acid,  H,P207; 

Metaphosphoric  acid,  HP03. 

Each  of  these  acids  forms  its  own  peculiar  metallic  salts. 

Tri-sodium  phosphate  (Na3PO,)  dissolved  in  water  precipitates  from  argentic 
nitrate  a  yellow  precipitate  of  triargentic  phosphate  (Ag,P04).  Sodium  pyro¬ 
phosphate  (Na,P2Or)  with  the  same  silver  salt  forms  a  white  precipitate,  con¬ 
sisting  of  Ag4P20;.  Sodium  metaphosphate  (NaP03)  forms  with  the  same 
silver  salt  —  argentic  nitrate — a  gelatinous  white  precipitate  (AgP03)  quite 
different  from  the  other  two. 

There  are  three  compounds  of  phosphorus  and  hydrogen.  One  is  a  solid, 
and  called  solid  phosphide  of  hydrogen  (HP2) ;  the  second  is  a  liquid,  termed 
liquid  phosphide  of  hydrogen  (H2P) ;  and  the  third  a  gas,  phosphuretted  hy¬ 
drogen  (H3P).  The  last-named  compound  has  the  peculiar  property  of  taking 
fire  spontaneously  when  brought  in  contact  with  the  air,  and  is  generally  pre¬ 
pared  by  placing  some  phosphorus  in  a  retort,  and  then  filling  the  latter,  neck 
and  body,  with  a  solution  of  caustic  potash.  By  boiling  the  solution  of  potash 
this  gas  is  eliminated,  and,  when  it  has  filled  the  upper  part  of  the  retort  and 
driven  the  fluid  out  of  the  neck,  every  bubble  that  escapes  takes  fire  sponta¬ 
neously,  forming  a  beautiful  ring  of  white  smoke.  Of  course  the  neck  of  the 
retort  must  be  kept  under  water,  and  if  it  is  allowed  to  dip  into  a  small  basin 
containing  more  solution  of  potash,  the  retort  and  its  contents  may  be  used 
for  several  days  to  show  the  evolution  of  phosphuretted  hydrogen ;  because, 
when  the  retort  is  allowed  to  cool,  solution  of  potash  fills  the  void  that  is 
created,  and  if  air  entered  instead  of  the  solution,  an  explosion  would  most 
likely  occur  that  might  burst  the  retort. 

There  are  chlorides,  bromides,  and  iodides  of  phosphorus,  and  a  phosphide 
of  nitrogen  called  phosphane  by  Gerhardt,  who  has  laboured  so  industriously 
to  reform  chemical  nomenclature. 

Sulphur  and  phosphorus  unite,  forming  compounds,  in  two  of  which  the 
molecules  unite  in  the  same  relative  proportions  as  phosphorus  anhydride 
(P»Oj)  and  phosphoric  anhydride  (P205),  the  corresponding  sulphur  compounds 
being  PaS3  and  PaSs. 


THE  METALS. 


TELLURIUM. 

Symbol,  Te.  Atomic  weight,  129.  Specific  gravity,  6*25. 

Henry  Watts,  in  his  “  Dictionary  of  Chemistry,”  agrees  with  other  scientific 
writers  in  stating  that  “this  element,  though  decidedly  metallic,  must  be  classed 
as  a  member  of  the  sulphur  family,  as  it  approximates  very  c  osely  in  its  che¬ 
mical  character  to  sulphur,  and  still  more  to  selenium.  It  was  first  identified 
as  a  distinct  metal  by  Klaproth  in  1798,  who  gave  it  the  name  ‘tellurium/ 
from  Tellus,  the  mythological  name  of  the  earth.  Tellurium  is  one  of  the 
rarer  metals,  being  found  in  a  few  localities  only,  and  chiefly  in  Hungary  and 
Transylvania.” 

“Tellurium  in  its  chemical  relations  bears  a  very  close  analogy  to  sulphur 
and  selenium.  It  forms  two  oxides— tellurous  oxide  (Te02)  and  telluric  oxide 
(TeOa) — which,  in  combination  with  water  and  with  metallic  bases,  yield  acids 
and  salts  analogous  to  those  formed  by  the  corresponding  oxides  of  sulphur 
and  selenium.” 

Tellurium  crystallizes,  and  has  a  bright  tin-like  metallic  lustre;  it  melts  at 
about  800  or  900°  F.,  and  at  a  high  temperature  is  converted  into  a  yellow 
vapour.  It  burns  when  strongly  ignited  in  air,  with  a  blue  flame  edged  with 
green,  emitting  a  peculiar  odorous  vapour.  Swallowed  in  minute  quantities, 
it  imparts  to  the  breath  a  s  rong  garlic  flavour. 

Telluretted  hydrogen  (H2Te)  is  a  gaseous  body  very  like  sulphuretted  hydro¬ 
gen;  in  fact,  its  odour  is  almost  identical  with  that  of  the  latter. 

Tellurium  is  a  bad  conductor  of  electricity  and  heat,  and  is  thus  early  spoken 
of  becuise  of  its  analogy  to  the  non-metalli;  bodies  sulphur  and  selenium. 


ARSENIC. 


G63 


ARSENIC. 

Symbol,  As.  Atomic  weight,  75.  Specific  gravity,  570  to  5-95. 

The  consideration  of  this  metal  is  entered  upon  here  because,  like  tellurium, 
it  has  certain  chemical  characteristics  which  place  it  closely  in  analogy  with 
non-metallic  elements,  viz.,  phosphorus  and  nitrogen  ;  at  the  same  time  it  has 
other  physical  qualities  that  bring  it  in  close  proximity  to  the  two  metals 
antimony  and  bismuth. 

Arsenic  may  be  regarded  as  an  intermediate  link  between  the  non-metallic 
bodies  already  considered  and  the  metallic  elements  which  have  next  to 
engage  our  attention.  In  the  brief  summary  of  each  metal,  its  sources,  and 
its  physical  and  chemical  properties,  will  be  considered. 


Sources  of  Arsenic. 


The  greater  part  of  the  arsenical  pyrites  (mispickel,  FeAsS),  from  which  the 
white  oxide  of  arsenic  is  procured,  is  found  in  Bohemia,  Norway,  Sweden, 
Hungary,  Saxony,  and  other  places  on  the  Continent.  Arsenic  occurs  as  an 
alloy  with  tin,  copper,  cobalt,  and  nickel ;  also  united  with  oxygen  and  certain 
metals,  as  in  the  arseniates  of  copper,  lead,  and  iron. 

There  are  natural  sulphides  of  arsenic,  viz.,  the  red  sulphide,  called  realgar, 
and  the  yellow,  termed  orpiment. 

Arsenic  is  occasionally  found  in  the  native- state,  and  is  one  of  the  most 
widely  diffused  natural  bodies,  being  sometimes  contained  even  in  mineral 

springs. 

White  arsenic,  arsenious  oxide,  or  trioxide  of  arsenic  (As203)  is  obtained  by 
roasting  the  sulphide  of  iron,  or  other  minerals  containing  arsenic,  in  a  rever¬ 
beratory  furnace  connected  with  a  long  chimney,  which  is  nearly  horizontal, 
but  terminating  in  a  tower  of  brickwork  also  divided  into  compartments,  so 
that  all  the  volatile  products  shall  be  condensed  during  the  slow  passage  of 
the  current  from  the  reverberatory  f  irnace. 

The  crude  arsenious  oxide  is  purified  by  sublimation,  and,  being  heated  in 
a  retort  with  charcoal,  is  reduced  to  metallic  arsenic,  which  sublimes  into  the 
receiver. 

Physical  Qualities  of  Arsenic. 


( I 


o 

3 


The  metallic  nature  of  arsenic  was  discovered  by  Brandt  in  1733-  ^  *s 

a  steel-grcv  colour,  easily  tarnishing  in  air,  but 
retaining  its  brilliant  aspect  under  water,  espe¬ 
cially  if  the  latter  is  first  boiled  and  placed  with 
the  arsenic  in  an  air-tight  bottle.  It  is  very 
brittle,  and  easily  pounded  in  a  mortar. 

Arsenic  has  no  smell  when  cold,  and,  if 
heated,  does  not  melt,  but  sublimes  easily,  and 
then  emits  a  strong  odour  resembling  garlic. 

Tubes  for  experiments  with  arsenic  may  be 
obtained  from  Mr.  How, of  I  oster  Lane,  Cheap- 
side.  A  certain  quantity  of  the  metallic  arsenic 
is  usually  oxidized  in  the  presence  of  air.  It  is 
a  most  violent  poison,  and  hence  derives  its 


FlC.  502. — Tubes  for  expt  Vi¬ 
vien  ting  with  Arsenie. 


664 


CHEMISTR  Y 


name  from  upcreviKov  (powerful),  on  account  of  the  small  quantity  sufficient 
to  cause  death. 

Chemical  Properties  of  Arsenic. 

Arsenic  combines  with  the  metals  like  sulphur  or  phosphorus,  and,  when 
heated  in  the  air,  ignites,  burning  with  a  bluish  flame  and  forming  arsenious 
oxide.  It  takes  fire  immediately  when  powdered  and  dropped  into  chlorine 
gas,  forming  arsenic  trichloride  (AsCls).  There  are  two  oxides  of  arsenic: 
the  sesquioxide  or  arsenious  anhydride,  arsenious  acid,  arsenic  trioxide  (As,Os), 
and  arsenic  anhydride,  arsenic  pentoxide,  or  arsenic  oxide  (As40,).  The  pre¬ 
paration  of  the  first-named  compound  has  already  been  described;  the  second, 
arsenic  pentoxide,  is  obtained  by  digesting  white  arsenic  with  nitric  acid,  and 
then  boiling  down  the  solution  in  a  platinum  or  hard  porcelain  vessel. 


Fig.  503. 

Hard  Porcelain  Cups  and  Cru¬ 
cibles  for  analytical  purposes. 


F IG.  504. — Portable  Sand  Bath  arid  Oven, 
heated  by  an  Oil  Lamp. 


In  the  absence  of  a  supply  of  coal-gas,  and  especially  where  operators  amuse 
themselves  in  the  country  with  chemical  experiments,  a  steady  moderate  heat 
is  often  required  for  the  solution  of  various  minerals  and  metals  in  acids  or 
other  solvents ;  this  is  conveniently  obtained  with  a  sand  bath  heated  by  a 
common  Argand  oil  lamp,  which  is  so  arranged  that  the  heat  shall  be  econo¬ 
mized,  and  whilst  imparting  it  to  the  sand  above,  a  small  oven  is  also  warmed, 
in  which  precipitates  or  filters  may  be  easily  dried. 

Arsenic  is  employed  for  various  purposes:  it  is  used  in  the  manufacture  of 
small  leaden  shot ;  it  enters  into  the  composition  of  the  alloys  of  tin  and 
copper  used  in  making  metallic  specula  for  telescopes.  In  fluxing  certain 
kinds  of  glass,  and  oxidizing  the  ferrous  oxide  to  get  rid  of  the  green  tinge,  it 
is  found  to  be  very  useful. 

There  are  many  pigments  which  owe  their  brilliancy  to  the  presence  of  this 
metal,  as  “  Scheele’s  green,”  or  hydrocupric  arsenic  (CaHAs03),  or  Schwein- 
furt  green,  a  cupric  arsenite  and  acetate  (3CaAs20„  Ca,C.H302). 

Arsenic  is  employed  to  prevent  smut  in  grain  and  in  poisoning  vermin,  and 
being  such  a  terrible  poison  easily  obtainable,  it  is  not  surprising  that  poor 


ARSENIC. 


665 


ignorant  criminals  should  use  it  for  destroying  human  life,  always  forgetting 
that,  although  so  readily  procured,  it  is  still  more  easily  detected. 

The  characteristic  results  obtained  by  using  the  proper  reagents  or  tests  for 
arsenic  are  unmistakable. 

The  testing  operations  for  arsenic  may  be  conducted  on  the  smallest  possible 
scale,  and  yet  are  most  conclusive,  and  for  this  purpose  plenty  of  clean  dry 
test  tubes  should  be  provided. 

B 


Fig,  505. 

a,  test  tubes  washed  and  draining,  to  be  placed  in  rack  b  for  use. 


The  identification  of  arsenic  may  be  conducted  with  quantities  so  minute 
as  to  be  inappreciable  by  the  balance.  The  presence  of  arsenic  in  any  mineral 
is  readily  detected  by  the  skilful  use  of  the  blowpipe.  A  fragment  of  mis- 
pickel  (FeAsS)  is  powdered,  and  heated  with  dry  carbonate  of  soda  and  char¬ 
coal  before  the  blowpipe,  a  well-trained  nose  soon  detects  the  peculiar  garlicky 
odour  when  the  heat  is  applied. 


Fig.  506. —  Various  Blowpipes  used  by  Chemists  and  Mineralogist . 


The  flame  of  a  spirit  lamp  will  answer  for  most  of  the  blowpipe  experiments, 
and  when  gas  is  laid  on  there  is  usually  a  jet  attached  to  the  mixed  air  and 
gas  burner  for  this  purpose.  As  an  illustration  of  the  convenience  of  the  gas 
burners,  Normandy’s  burner  with  blowpipe  gas  jet  is  shown  in  fig.  507. 

When  in  solution,  the  compounds  of  arsenic  are  detected  by  the  following 
tests  • 

If  the  arsenic  be  in  the  condition  of  arscnious  acid,  and  supposing  the 
organic  matters  removed  by  processes  all  described  in  works  on  toxicology, 


666 


CHEMISTRY. 


solution  of  nitrate  of  silver  with  a  drop  of  ammonia  causes  a  yellow  precipi¬ 
tate  of  triargentic  arseniate,  freely  soluble  in  excess  of  ammonia  or  in  nitric 
acid.  Sulphuretted  hydrogen  causes  a  yellow  precipitate  of  arsenious  sesqui- 
sulphide :  this  must  be  allowed  to  subside,  and  is  then  collected,  dissolved  in 

ammonia,  and  evaporated  to  dryness 
on  a  water  bath.  The  dry  sesquisul- 
phide  is  reduced  to  the  metallic  state 
by  mixing  it  with  some  potassic  cy¬ 
anide  and  sodic  carbonate,  all  well 
dried  and  mixed;  and  placing  it  into 
one  of  the  tubes,  Fig.  502,  the  mixture 
is  now  heated  strongly  by  the  blow¬ 
pipe,  and  the  metallic  arsenic  con¬ 
denses  in  the  upper  part  of  the  tube, 
giving  to  it  the  appearance  of  a  bril¬ 
liant  mirror  having  a  steel-grey  aspect. 
Solution  of  sulphate  of  copper  with  a 
drop  or  so  of  ammonia  throws  down 
a  green  precipitate,  hydrocupric  ar- 
senite  or  Scheele’s  green.  A  little 
solution  of  arsenious  acid  evaporated 
to  dryness  with  nitric  acid,  and  con¬ 
verted  into  arsenic  acid,  and  then  re¬ 
dissolved  with  the  addition  of  a  drop  of  ammonia,  gives  the  marked  brick-red 
precipitate,  when  a  solution  of  nitrate  of  silver  is  added.  The  brick-red  pre¬ 
cipitate  is  triargentic  arseniate  (Ag3AsO.). 

Marsh’s  test  is  one  of  the  most  conclusive  when  the  inquiry  is  made  for 
judicial  purposes.  A  bottle,  A,  fitted  with  a  cork  and  small  funnel,  is  charged 
with  pure  granulated  zinc  and  water;  to  this  is  adapted  a  tube,  B,  containing 
calcic  chloride,  to  stop  any  particles  of  fluid  that  might  be  carried  over  mecha¬ 
nically  ;  to  the  last-named  tube  is  attached  a  bulb,  C,  drawn  out  to  a  capillary 


Fig.  507. — Dr.  Normandy s  Burner , 
with  independent  Blowpipe  Flame. 


Fig.  508. — Marsh's  Test  for  Arsenic. 


tube,  and  made  of  hard  German  glass,  and  under  which  (when  all  the  atmo¬ 
spheric  air  is  driven  out  by  the  current  of  hydrogen  formed  by  pouring  pure  sul¬ 
phuric  acid  down  the  funnel  attached  to  a)  the  flame  of  a  spirit  lamp  is  placed, 
at  the  point  just  where  the  capillary  portion  of  the  bulb  tube  commences.  Ten 
minutes  are  allowed  to  ascertain  if  all  the  materials  are  pure,  and  that  no  de¬ 
posit  whatever  takes  place  in  the  bulb.  The  solution  supposed  to  contain  the 


ANTIMONY. 


667 


arsenious  acid  is  now  poured  down  the  funnel  into  A,  and,  if  arsenic  be  pre¬ 
sent,  arseniuretted  hydrogen  (H:1As)  is  formed,  and  decomposed  as  it  passes 
through  the  heated  tube,  the  metal  being  deposited  like  a  ring  of  burnished 
steel  just  beyond  the  part  where  the  heat  is  applied.  Marsh’s  test,  taken  in  con¬ 
junction  with  Reinsch's  test  and  the  others  already  described,  affords  evidence 
which  is  indisputable.  The  arseniuretted  hydrogen,  if  allowed  to  escape  through 
the  cold  bulb  and  inflamed  at  the  aperture,  burns  with  the  peculiar  flame  of 
arsenic;  and  if  a  cold  piece  of  porcelain  be  held  against  the  flame,  rings  of 
metallic  arsenic  are  deposited,  distinguishable  from  antimony,  which  behaves 
in  a  similar  manner,  by  the  fact  that  antimonial  stains  disappear  when  a  drop 
of  ammonia  sulphide  in  which  a  little  sulphur  is  dissolved  is  added,  whilst  the 
arsenical  crusts  are  hardly  affected  by  the  same  re-agent. 


ANTIMONY. 

Symbol,  Sb  (Stibium).  Atomic  weight,  122. 

It  has  already  been  mentioned  that  arsenic,  antimony,  and  bismuth  closely 
resemble  phosphorus  in  their  chemical,  though  not  exactly  in  their  physical, 
qualities;  this  group  of  three  metals  is  therefore  taken  first,  because  it  is  the 
connecting-link  between  the  non-metallie  and  metallic  elements. 

Sources  whence  Derived. 

Antimony,  though  sometimes  found  native,  is  chiefly  derived  from  the  ore 
or  sesquisulphide  (Sb2S3),  which  is  found  in  Hungary,  Norway,  Saxony,  and 
Sweden.  This  ore  is  first  purified  from  the  earthy  matter:  by  exposure  to  a 
strong  heat  in  a  reverberatory  furnace  the  ore  melts  and  separates  from  the 
impurities,  and  is  cast  into  cakes  called  crude  antimony. 


Fig.  509 .—  Useful forms  0/  Furnaces,  with  Sand  Bath  and  Oven , 

And  various-sized  rings  and  iron  pots  for  chemical  purposes. 


If  4  parts  of  crude  antimony,  3  of  crude  tartar,  and  1  \  of  nitre  are  thorough  y 
powdered  and  mixed,  and  thrown  gradually  into  a  Hessian  crucible  kept  at  a 
bright  red  heat,  the  ore  is  reduced  to  the  metallic  state.  A  furnace  with  a 
capacious  and  tall  chimney  can  be  built  so  that  the  whole  draught  is  con- 


o68 


CHEMISTR  Y. 


nected  with  the  fireplace,  or  diverted  when  required,  by  proper  dampers,  to  a 
sand  bath,  as  at  A,  Fig.  509,  or  it  may  heat  an  oven  and  sand  bath,  as  at  B,  Fig. 
509- 

Physical  Properties  of  Antimony. 

This  metal  was  discovered  by  Basil  Valentine  at  the  latter  end  of  the  fif¬ 
teenth  century,  and  is  so  called  from  the  Greek  am,  against,  and  yuotos,  a 
monk,  because  it  is  stated  that  some  monks  were  unfortunately  poisoned 
by  medicine  prepared  from  this  metal.  Antimony  is  crystalline  and  has  a 
brilliant  silvery-white  aspect,  and,  having  very  little  tenacity  or  ductility,  is 
therefore  easily  powdered.  The  specific  gravity  of  this  metal  is  6715,  and  it 
melts  at  about  1,150°  F.  It  is  used  in  forming  various  important  alloys,  such 
as  type  and  britannia  metals  and  pewter.  The  well-known  medicine  called 
James’s  Powder  contains  this  metal  and  “tartar  emetic;”  a  true  chemical  com¬ 
pound  of  potassium,  oxide  of  antimony,  tartaric  acid,  and  water  is  also  exten¬ 
sively  used  in  the  healing  art. 

Chemical  Properties  of  Antimony. 

Antimony  retains  its  brilliancy  when  exposed  to  the  air;  but  if  melted 
rapidly  it  changes  by  combining  with  the  oxygen  of  the  air.  If  the  heat  is 
strongly  urged  it  will  burn  with  a  white  flame,  forming  a  heavy  white  smoke 
— the  antimoric  trioxide.  Powdered  antimony  takes  fire  when  thrown  into 
chlorine  gas,  and  becomes  very  hot  if  brought  in  contact  with  iodine  and  bro¬ 
mine,  with  which  it  also  unites.  Aqua  regia,  nitro-hydrochloric  acid,  dis¬ 
solves  antimony  freely ;  if  nitric  acid  be  used  alone,  the  metal  is  converted 
into  a  straw-coloured  insoluble  antimonic  oxide:  boiling  hydrochloric  acid  will 
dissolve  it.  Metallic  antimony  is  also  dissolved  when  digested  in  fine  powder 
with  a  solution  of  one  of  the  sulphides  of  potassium. 

Antimony  forms  three  oxides : 

Antimonious  oxide,  Sb203; 

Antimonic  oxide  or  anhydride,  Sb2Cb ; 

Antimonious  antimoniate,  Sb203Sb205. 

It  is  the  first  of  these  oxides  which  is  used  in  medicine. 

This  metal-like  arsenic  unites  with  hydrogen,  forming  antimoniuretted  hy¬ 
drogen,  having  the  probable  constitution  of  SbH,,  and  is  evolved  whenever 
the  metal  is  brought  in  contact  with  zinc  and  dilute  sulphuric  acid. 

There  are  many  niceties  required  in  the  discrimination  of  this  metal  from 
arsenic ;  and  as  both  metals  are  used  by  poisoners,  the  reader  is  referred  to 
the  best  works  on  toxicology  for  the  analytical  processes  required,  not  only  to 
detect  antimony,  but  also  to  distinguish  it  from  arsenic. 


BISMUTH. 

Symbol,  Bi.  Atomic  weight,  210. 

Sources  whence  Derived. 

Bismuth,  though  not  a  rare  metal,  is  by  no  means  abundantly  distributed 
throughout  the  crust  of  the  earth.  It  occurs  native  in  Saxony,  Bohemia,  and 
Transylvania,  and  is  simply  melted  out  of  the  crushed  quartz  with  which  it  is 


BISMUTH. 


669 


associated.  It  also  occurs  with  cobalt  in  the  cobaltic  ores  of  Saxony  and 
England.  A  sulphide  of  bismuth,  called  “  bismuth  glance  ”  (Bi2S3),  is  anothei 
natural  mineral  containing  this  metal. 

•  Physical  Properties. 

In  some  works  bismuth  is  described  as  a  yellowish-white  metal,  but  it  is  in 
fact  reddish-white:  this  apparent  difference  in  the  bloom  or  tint  of  the  metal 
was  observed  by  the  discoverer  Agricola  in  1529,  who  called  it  “  Wiessmatte ,” 
“a  blooming  meadow,”  on  account  of  the  variegated  hues  of  its  tarnish.  It 
has  a  specific  gravity  of  9799,  reduced  by  Marchand  and  Scheerer  (who, 
apparently,  compressed  the  internal  cavities  in  the  specimen  of  bismuth  they 
used)  to  9'5S6.  The  metal  is  easily  fusible,  and  melts  at  a  temperature  of 
507°  F.  Bismuth,  like  antimony  and  arsenic,  has  little  malleability,  ductility, 
or  tenacity,  and  is  so  brittle  that  it  may  be  easily  reduced  to  powder  under  the 
hammer. 

On  account  of  the  singular  property  it  possesses  of  expanding  when  cooling 
it  is  extremely  valuable  in  testing  the  progress  of  a  die,  and  is  therefore  con¬ 
stantly  employed  by  die-sinkers,  who,  with  type-makers,  call  it  “  tin  glass.” 

Chemical  Properties. 

Bismuth  is  slightly  volatile  when  strongly  heated,  and,  like  arsenic,  tarnishes 
in  the  air,  but  not  so  if  kept  in  a  well-stoppered  bottle  containing  boiled  dis¬ 
tilled  water.  At  a  red  heat  bismuth  quickly  oxidizes,  and  also  takes  fire  in 
chlorine  when  very  finely  powdered  and  dropped  into  that  gas.  Sulphur,  bro¬ 
mine,  and  iodine  all  unite  with  this  metal. 

Bismuth  is  quickly  dissolved  by  nitric  acid,  which  is  its 
proper  solvent. 

Two  oxides  of  bismuth  are  known  :  bismuth  oxide  or 
sesquioxide  of  bismuth  (Bi203),  and  an  acid  oxide  or  an¬ 
hydride  (Bi2Oj). 

The  nitrate  (Bi3N035H.0)  appears  to  be  the  best  known 
and  most  important  salt  of  bismuth.  When  the  solution  is 

largely  diluted  with  water,  an  insol¬ 
uble  basic  compound  is  formed,  or 
sub-nitrate  (Bi2032HN03).  This 
precipitate,  when  collected  and  mo¬ 
derately  washed  and  dried,  is  the 
well-known  cosmetic,  so  freely  pre¬ 
scribed  by  the  improvers  of  com¬ 
plexions,  called  “  pearl  white.”  I  he 
old  alchemical  writers  called  it  the 
“magistery  of  bismuth.”  For  drying 
precipitates  various  convenient 

Fig.  510. 

a,  oven  heated  by  foiling  water  >  b,  hot  air  oven,  heated  by  gas,  oil,  or  a  spirit  lamp 

ovens  are  made  by  Mr.  How,  of  Foster  Lane.  When  surrounded  by  water 
and  the  steam  allowed  to  escape  freely,  the  oven,  of  course,  does  not  afford  a 
heat  higher  than  21 2°  F. 


670 


CHE  MIS  TR  Y. 


The  hot  air  oven  is  heated  from  below  with  a  gas-flame ;  a  much  higher 
temperatuie  may  be  obtained,  and  conveniently  regulated  by  a  thermometer. 
No  solder  is  used  in  the  construction  of  these  ovens,  which  are  most  useful 
for  drying  precipitates. 

The  general  chemical  analogy  between  nitrogen,  phosphorus,  arsenic,  anti¬ 
mony,  and  bismuth  is  well  shown  by  tabulating  some  of  the  compounds  having 
t  e  same  number  of  combining  molecules. 


N*03 

p*o3 

As203 

Sb203 

Bi2Os 


Nitrous  anhydride. 
Phosphorus  do. 
Arsenious  do. 
Antimonious  do. 
Bismuthous  do. 


CLASSIFICATION  OF  THE  METALS. 

Although  the  metal  tellurium,  and  the  group  of  metals,  arsenic,  antimony, 
and  bismuth,  have  been  discussed  because  of  their  remarkable  anology  to 
certain  bodies  belonging  to  the  non-metallic  substances,  the  arrangement  of 
the  whole  of  the  metals  in  proper  groups  must  not  be  omitted,  because  the 
student  is  so  much  assisted  by  studying  them  not  only  individually,  but  in 
their  relations  to  each  other. 

Gmelin  arranges  the  metals  in  six  groups.  Dr.  Miller  in  eight,  and  Professor 
Roscoe  in  eleven  classes,  the  latter  of  which  will  be  adopted. 

I.  Metals  of  the  Alkalies  (five  in  number). 

1.  Potassium  3.  Lithium  5.  Rubidium 

2.  Sodium  4.  Caesium  (?)  Ammonium 

II.  Metals  of  the  Alkaline  Earths  (three  in  number). 

1.  Barium  2.  Strontium  3.  Calcium 

III.  Metals  of  the  Earths  (nine  in  number). 


1. 

Aluminium 

4.  Erbium 

7- 

Lanthanum 

2. 

Glucinium 

5.  Zirconium 

8. 

Didymium 

3- 

Y  ttrium 

6.  Cerium 

9- 

Thorium 

IV.  Zinc  Class  (three  in 

number). 

1. 

Magnesium 

2.  Zinc 

3- 

Cadmium 

V.  Iron  Class  (seven  in 

num  er). 

1. 

Cobalt 

3.  Uranium 

6. 

Manganese 

2. 

Nickel 

4.  Iron 

5.  Chromium 

7. 

Indium 

VI.  Tin  Class  (four  in 

number). 

1. 

Tin  2.  Titanium  3.  Niobium  4. 

Tantalum 

VII.  Tungsten  Class  (three  in  number). 

I.  Molybdenum  2.  Vanadium  3.  Tungsten 


VIII.  Arsenic  Class  (three  in  number). 

I.  Arsenic  2.  Antimony  3.  Bismuth 


POTASS /C/M. 


671 


IX.  Lead  Class  (two  in  number). 

I.  Lead  2.  Thallium 

X.  Silver  Class  (three  in  number). 

2.  Mercury  3.  Silver 

XL  Gold  Class  (seven  in  number). 

3.  Palladium  6.  Iridium 

4.  Rhodium  7.  Osmium 

5.  Ruthenium 


CLASS  I. 

POTASSIUM,  SODIUM,  RUBIDIUM,  CESIUM,  LITHIUM, 

AMMONIUM. 

Metals  of  the  Alkalies . 


POTASSIUM. 

Symbol,  K  (Kalium).  Atomic  weight,  39' 1. 

Potassium  monoxide  (KzO),  united  with  water,  forms  potassium  hydrate 
(HKO),  commonly  called  potash ,  and  gives  the  name  to  this  metal,  so  called 
from  the  pots  in  which  the  ashes  of  land  plants,  wood,  &c.,  were  lixiviated, 
boiled,  and  evaporated  to  the  dry  substance  called  pot-ashes.  It  was  disco¬ 
vered  by  Davy  in  1807. 

Sources  whence  Derived. 

Our  daily  food,  made  up  of  animal  and  vegetable  substances,  most  of  which 
contain  salts  of  potassium,  conveys  to  the  human  body  this  metal,  which 
appears,  in  combination  with  other  elements,  to  be  an  essential  constituent  of 
flesh,  milk,  &c. 

This  element  is  very  plentifully  distributed  throughout  the  mineral  world. 
It  is  found  as  a  nitrate  in  the  soils  of  certain  hot  climates;  in  sea-water,  in 
certain  springs,  also  in  salt  deposits  are  to  be  found  iodides,  bromides,  and 
chlorides  of  potassium.  Feldspar  and  mica  are  examples  of  common  mineral 
bodies  that  contain  potassium  in  the  form  of  silicates. 

When  plants  and  trees  are  burnt,  the  organic  acids  with  which  the  potash 
was  united  are  changed  to  carbonates,  and  thus  the  wood-ashes  contain  pot- 
assic  carbonate  (K2C05).  The  commercial  process  now  approved  for  obtain¬ 
ing  potassium  is  that  of  decomposing  potassic  carbonate  by  charcoal.  Crude 
tartar  —  formerly  called  bitartrate  of  potash,  but  now  termed  hydro-potassic 
tartrate,  being,  in  fact,  the  crust  deposited  from  wine — is  first  heated  in  a 
covered  crucible  until  all  vapours  cease  escaping;  the  residue,  a  porous  mass 
consisting  of  potassic  carbonate  and  finely-divided  charcoal,  is  broken  up  into 
lumps,  and  transferred  to  a  wrought-iron  bottle  (such  as  that  delineated  on 
page  545),  provided  with  an  iron  tube  ;  the  bottle  is  supported  in  a  proper 
furnace,  ana,  when  red  hot,  is  dusted  over  with  powdered  fused  borax:  this 
simple  coating  protects  the  botrie  from  oxidation,  and  enables  the  heat  to  be 
gradually  raised  to  a  full  white  neat.  When  the  vapour  of  potassium  begins 
to  appear  and  burns  with  a  brilliant  light,  a  peculiar  shaped  receiver  is  attached, 


1.  Copper 

1.  Gold 

2.  Platinum 


672 


CHEMISTR  Y 


and  kept  cool  with  a  damp  cloth.  The  receiver  is  attached  as  close  as  pos¬ 
sible  to  the  generating-bottle,  and,  should  the  potassium  choke  up  the  neck, 
a  provision  is  made  to  remove  the  obstruction  with  a  sliding  rod.  Finally, 
the  receiver  is  plunged  into  Persian  naphtha,  and  when  cold  the  potassium  is 
removed  and  preserved  under  naphtha.  The  crude  potassium  is  always  re¬ 
distilled,  to  get  rid  of  a  peculiar  black  detonating  compound,  and,  when 
required  very  pure,  is  even  distilled  again. 

Physical  Properties  of  Potassium. 

This  metal  has  a  specific  gravity  of  o'865,  and  is  the  lightest  of  all  metab 
except  lithium :  its  specific  gravity  shows  that  it  will  float  on  water.  At  o3  F.  it 
is  crystalline  and  brittle,  and  at  ordinary  temperatures  is  very  malleable — or 
rather,  in  this  case,  soft  and  pasty — and  becomes  perfectly  liquid  at  144°  5'  F. 
Two  clean  surfaces  are  easily  welded  or  squeezed  together;  indeed,  the  ordi¬ 
nary  terms  as  applied  to  other  metals — such  as  malleability,  ductility,  and 
tenacity — may  be  exchanged  for  the  general  one  of  plasticity. 

Potassium  is  a  bluish-white  metal,  and,  when  freshly  cut,  retains  its  brilliancy 
for  a  short  time  only,  being  speedily  covered  with  oxide.  Potassium  may  be 
crystallized  by  melting  some  in  a  sealed  tube,  and  just  at  the  point  of  solidifi¬ 
cation,  when  a  few  solid  points  appear,  if  the  fluid  portion  is  poured  away  by 
inverting  the  tube,  the  residue  crystallizes  in  the  form  of  shining  octohedral 
crystals. 

Chemical  Properties. 

Potassium  burns  with  a  violet  light  when  heated  in  the  air,  or,  if  thrown  on 
water,  is  so  rapidly  oxidized  and  heated  that  the  escaping  hydrogen  takes  fire, 
and  burns  with  a  rose-red  flame,  because  some  of  the  potassium  volatilizes  and 
burns  with  it.  The  resulting  potassic  hydrate  (KHO)  takes  the  form  of  a 
liquid  red-hot  ball,  and,  gradually  cooling,  appears  like  glass ;  and  then  coming 
in  contact  with  the  water,  from  which  it  was  repelled  whilst  hot  by  the  escaping 
vapour  on  the  spheroidal  system,  it  bursts  into  a  number  of  small  particles,  any 
one  of  which  entering  the  eye  would  cause  great  pain.  Each  atom  of  potassium 
displaces  half  the  hydrogen  of  an  atom  of  water,  and  potassium  hydrate  is 
formed. 

2H.O  +  K2  =  2KHO  +  H2 

Water.  Totassium  Fotash.  Hydrogen. 

There  are  three  distinct  oxides  of  potassium,  viz. — 

1.  Potassium  dioxide .  .....  K202 

2.  Potash  or  potassium  monoxide  .  .  .  K20 

3.  Potassium  tetroxide  or  peroxide  of  potassium  K20* 

The  chief  salts  of  this  metal  are  potassium  carbonate  (K2C03) ;  potassium 
nitrate,  nitre  or  saltpetre  (KN03),  used  so  extensively  in  the  manufacture  of 
gunpowder,  which  contains 

Nitre  ....  75  parts  by  weight, 

Charcoal  „  .  .15  „  „ 

Sulphur  .  .  .10  „  „ 

100 

Potassium  chlorate  (KC10S),  already  mentioned  as  an  important  source  of 
oxygen  gas;  and  potassium  sulphate  (K2S04). 


SODIUM. 


673 


Potassium  forms  various  compounds  with  sulphur,  viz.— K2S,  K2Sj,  KaSs, 
and  K.S*  It  also  unites  with  chlorine,  iodine,  bromine,  and  fluorine,  and 
curiously  absorbs  a  large  quantity  of  hydrogen  (HK,)  at  a  dull  red  heat,  but 
gives  off  the  gas  again  at  a  higher  temperature. 

The  tests  tor  salts  of  potassium  are  applied  after  all  other  metals  except 
sodium  are  removed.  The  solutions  tested  should  be  concentrated,  and  for 
this  purpose  hard  porcelain  dishes,  with  or  without  handles,  also  strainers  and 
ladles  for  dipping  out  any  crystals  for  examination  with  a  magnifying-glass, 
can  be  obtained  from  Mr.  How. 


Fig.  5 1 1. 

a,  b.  evapotating-dishes;  c,  n.  porcelain  trainers. 


The  concentrated  fluid  supposed  to  contain  potash  is  tested  with  a  solution 
of  tartaric  acid  in  excess,  and,  if  briskly  stirred,  crystals  of  hvdro-potassic  tar¬ 
trate  (KHC4H40«)  are  formed.  The  best  test  is  platinic  chloride,  which  forms 
a  yellow  double  salt  with  potash  (2KCI,  PtCl*),  insoluble  in  alcohol  and  ether, 
but  slightly  soluble  in  water. 


SODIUM. 

Symbol,  Na  (Natrium).  Atomic  weight,  23. 

This  metal  was  also  discovered  by  Davy  in  1808,  and  is  so  called  from  the 
alkali  soda,  originally  obtained  from  the  ashes  of  the  Salsola  ^oda. 


Sources  whence  Derived. 

Sodic  chloride,  or  common  salt,  is  of  course  the  great  source  from  which 
this  metal  is  obtained.  Sodic  chloride  exists  in  solid  beds  in  Cheshire,  or  is 
obtained  by  the  evaporation  of  sea-water.  Common  salt  is  converted  into 
sodic  carbonate,  and  from  this,  by  the  action  of  charcoal  mixed  with  chalk, 
and  with  the  assistance  of  an  intense  heat,  sodium  is  now  obtained  at  a  very 
cheap  rate.  The  process  is  very  much  like  that  required  in  the  manufacture 
of  potassium,  and  the  metal  is  now  used  extensively  in  the  preparation  of 
aluminium,  magnesium,  &c. 

Physical  Properties. 

Sodium  is  a  silver-white  metal  with  a  bluish  aspect,  plastic  and  soft  like 
potassium  at  ordinary  temperatures,  and  fusing  at  207°  7'  F.  When  dropped 

43 


674 


CHEMJSTR  Y 


into  cold  water  it  does  not  appear  to  produce  enough  heat  to  set  fire  to  the 
hydrogen  escaping  around  it ;  if,  however,  the  water  is  thickened  with  starch, 
or  hot,  or  if  the  sodium  is  placed  on  a  piece  of  wetted  blotting-paper,  the  heat 
accumulates,  and  then  the  hydrogen  burns  with  the  metal,  which  emits  a 
bright  yellow  light.  The  specific  gravity  of  sodium  is  0*972. 

Chemical  Properties. 

Sodium  volatilizes  at  a  heat  below  redness ;  it  tarnishes  directly  it  is  ex¬ 
posed  to  the  air,  and  forms  two  oxides: 

Soda  or  sodic  oxide  .  ....  Na20  =62. 

Sodic  peroxide . Na202  =  7S. 

The  chief  salts  are  sodic  chloride  (NaCl),  sodic  nitrate  or  cubic  nitre 
(NaN03),  and  sodic  carbonate  (Na2C03);  the  latter  represents  in  its  manu¬ 
facture  one  of  the  great  commercial  elements  of  wealth  in  this  country,  and 
involves  processes  conducted  on  the  largest  scale  by  which  common  salt  is 
converted  into  “  salt  cake,”  then  into  “  black  ash,”  and  finally,  by  lixiviation 
and  evaporation,  the  soda-ash — viz.,  the  carbonate — is  obtained. 

The  phosphates  of  sodium,  sodium  borate,  or  borax  (Na.202,  B203-F  ioH20), 
the  sodic  silicates  or  soluble  glass,  and  sodic  hyposulphite  (Na2S2H204+4H20), 
used  in  photography,  are  other  examples  of  useful  sodium  salts. 

Sodium  is  recognized  by  the  yellow  colour  it  imparts  to  flame,  and  all  the 
sodium  salts  except  theantimoniace  being  soluble  in  water,  the  detection  of  this 
metal  is  effected  rather  by  a  negative  than  a  direct  process.  The  spectroscope 
is  most  usefully  applied  in  this  and  many  other  cases  where  the  presence  of  a 
minute  quantity  of  any  metal  is  suspected. 

- ♦ - 

RUBIDIUM. 

Symbol,  Rb.  Atomic  weight,  85*54. 

This  metal,  so  called  from  the  Latin  rubidus,dtaxk  red,  was  first  discovered 
with  the  spectroscope  by  Bunsen  and  Kirchoff  between  i860  and  ’61.  It  is 
said  to  be  a  white  metal  capable  of  rapid  oxidation,  and  having  a  specific 
gravity  of  1*52.  It  is  present  in  small  quantities  in  lepidolite,  and  was  origin¬ 
ally  discovered  in  the  mineral  water  of  Durkheim.  At  140  F.  it  is  soft,  and 
melts  at  ioi°  3'  F.  At  a  temperature  below  a  dull  red  heat  it  is  converted  into 
a  blue  vapour  shaded  with  green.  Like  potassium,  rubidium  takes  fire  when 
thrown  upon  water. 

Rubidia  (Rb20)  is  the  only  oxide  of  rubidium  known,  and  rubidic  chloride, 
sulphate,  nitrate,  carbonate,  and  hydro-rubidic  carbonate  or  bicarbonate  are 
some  of  the  salts  of  this  rare  metal  which  have  already  been  investigated. 


CESIUM. 

Symbol,  Cs.  Atomic  weight,  133, 

This  metal  was  also  discovered  by  spectrum  analysis,  and  so  called  by  its 
discoverers,  Bunsen  and  Kirchoff,  from  ccesius ,  sky-blue,  in  allusion  to  the  two 
brilliant  blue  bands  produced  by  it  in  the  flame  used  for  its  volatilization. 


LITHI UM—A  MM  ON l  UM. 


675 


Some  idea  of  the  searching  nature  of  spectrum  analysis  may  be  formed  from 
the  fact  that  140  gallons  of  the  Diirkheim  water  in  which  it  was  first  dis¬ 
covered  contain  only  one  grain  of  a  salt  of  caesium.  Pisani  has,  however, 
discovered  caesium  in  a  rare  mineral  called  Pollux,  found  in  the  island  of  Elba: 
the  mineral  contained  32  per  cent,  of  caesium. 

Caesia  (Cs*0),  caesic  chloride  (CsCl),  caesic  sulphate  (CSiSO,),  caesic  nitrate 
(CsNOj),  and  caesic  carbonate  (Cs2C04)  arc  some  of  the  compounds  of  this 
metal  which  have  been  obtained. 

Both  rubidium  and  caesium  closely  resemble  each  other  and  potassium,  and 
caesium  is  separated  from  rubidium  by  taking  advantage  of  the  greater  solu¬ 
bility  of  the  caesic  tartrate. 


LITHIUM. 

Symbol,  Li.  Atomic  weight,  7. 

Lithium  (from  A.i0o?,  a  stone)  was  formerly  supposed  to  be  a  very'  rare 
metal,  but,  since  the  use  of  the  spectroscope,  is  found  to  be  contained  in 
various  mineral  springs,  the  ashes  of  tobacco,  and  in  certain  micas  and  feld¬ 
spars.  Lepidolite  or  lithic  mica,  triphane  or  spodumene,  and  petalite  are  the 
three  minerals  that  contain  it  in  the  largest  quantity,  and  even  that  is  small, 
and  docs  not  exceed  from  3  to  6  per  cent. 

The  specific  gravity  of  lithium  (the  lightest  solid  known)  is  only  C5936.  It 
volatilizes  at  high  temperatures.  If  thrown  on  water  it  behaves  very  much 
like  sodium,  and  produces  a  most  intense  heat  when  burnt  In  the  air.  It  is 
usually  prepared  by  decomposing  the  fused  chloride  by  electricity.  The  metal 
is  of  a  white  colour,  and  melts  at  336°  F. 

Lithia(L.O),  lithic  hydrate (L1IO),  lithic  chloride,  sulphate,  phosphate,  and 
carbonate  have  been  examined,  and  all  the  volatile  lithium  salts  impart  a 
beautiful  crimson  tinge  to  flame.  The  spectrum  of  lithium  is  one  of  the  most 
beautiful  that  can  be  projected  on  to  the  disc  by  the  electric  lamp  and  voltaic 
battery. 

- « - 

AMMONIUM. 

Theoretical  atomic  weight  =  18. 

It  has  long  been  supposed  that  there  exists  another  metal,  or  quasi  metal 
(NH4),  called  ammonium;  thus  ammonium  chloride  (II  NCL),  the  most  im¬ 
portant  of  the  salts  derived  from  ammonium,  when  employed  in  solution  to 
moisten  an  amalgam  of  potassium  and  sodium,  causes  the  latter  to  increase 
eight  or  ten  times  in  bulk.  The  appearance  of  the  swelled-out  amalgam  is 
peculiar:  it  retains  its  brilliancy,  at  t lie  same  time  appears  pasty;  and  il  this 
body  is  reduced  in  temperature  to  zero  or  o'  F.,  it  assumes  the  solid  condition, 
and  crystallizes  in  cubes.  In  the  pasty  st;  te  it  gradually  decomposes  spon¬ 
taneously,  but  more  rapidly  when  placed  in  water,  when  hydrogen  escapes,  and 
ammonia  is  found  in  solution.  A  metal  is  always  defined  to  be  an  element; 
how  then  can  NH,  belong  to  that  class?  Is  it  not  more  probable  that  hydro¬ 
gen  is  really  the  metal  that  puffs  out  and  combines  w.th  the  mercury?  The 
idea  receives  a  remarkable  corroboration  from  the  fo.lo.ving  experiment,  which 
the  writer  was  kindly  shown  by  Mr.  Roberts: 


43 — 2 


676 


CHEMISTR  Y. 


“  Hydrogenium  a  Metal. — At  the  Royal  Society’s  con7>ersazione ,  Mr.  W.  C. 
Roberts  (for  Mr.  Graham,  the  Master  of  the  Mint)  exhibited  a  curious  ex¬ 
ample  of  the  absorption  of  hydrogen  by  palladium,  and  consequent  alloy  and 
expansion  of  the  metal.  A  coiled  ribbon  of  palladium  was  attached  to  each 
pole  of  a  small  battery  in  a  water  bath.  The  current  being  turned  on,  the 
ribbon  absorbs  hydrogen,  expands,  uncoils,  and  stretches  itself  across  the 
bath ;  then,  on  reversal  of  the  current,  shrinks,  and  re-forms  its  coil,  while  the 
opposite  ribbon  goes  through  the  opposite  process.  The  appearance  is  that 
of  two  worms  wriggling  alternately  to  and  fro  across  the  bath.  In  another 
instance  the  expansion  was  shown  by  a  red-tipped  arrow  making  bold  sweeps 
half  round  a  circle.  These  experiments  demonstrate  the  enormous  capacity 
of  palladium  for  absorption  of  hydrogen,  and  verify  Mr.  Graham’s  conclusions.” 


CLASS  II. 

CALCIUM,  STRONTIUM,  BARIUM. 

Metals  of  the  Alkaline  Earths. 

CALCIUM. 

Symbol,  Ca.  Atomic  weight,  40. 

Mountain  limestone,  marble,  chalk,  gypsum,  marls,  and  various  soils  are 
all  common  sources  from  whence  this  metal  may  be  derived.  It  is,  however, 
usually  procured  from  calcium  iodide  by  the  action  of  metallic  sodium,  and  is 
then  described  as  a  yellow  metal,  like  pale  gold,  having  a  specific  gravity  of 
1*580.  Calcium  was  discovered  by  Davy  in  the  year  1808,  and  obtained  by 
him  from  lime,  a  substance  long  called  a  calx  or  earth.  In  hardness  calcium 
takes  an  intermediate  position  between  gold  and  lead,  and  can  be  beaten  into 
very  thin  leaves.  When  exposed  to  dry  or  damp  air,  it  tarnishes  and  is  gradu¬ 
ally  oxidized.  When  heated,  it  burns  with  a  white  light,  forming  the  only 
oxide,  called  calcic  oxide  or  lime  (CaO),  sometimes  termed  quicklime,  to  dis¬ 
tinguish  it  from  the  hydra'  e  of  lime  or  calcic  hydrate  (CaH„02). 

The  use  of  lime  in  the  mixtures  called  mortars  and  cements,  also  in  hydraulic 
mortars,  and  for  many  other  useful  purposes,  is  well  known.  The  salts  of  lime 
are  far  too  numerous  to  be  considered  here.  The  most  important  are  calcic 
carbonate  (CaCO-,),  calcic  sulphate  (CaS04),  calcic  phosphate  (Caa2P04),  and 
calcic  fluoride  (CaFL). 

- ♦ - 

STRONTIUM. 

Symbol,  Sr.  Atomic  weight,  87*5. 

Another  of  the  metals  discovered  by  Davy  in  1808,  and  so  called  because 
obtained  from  a  mineral  originally  noticed  by  Dr.  Hope,  and  called  stron- 
tianite,  the  strontic  or  strontium  carbonate  (SrC03). 

It  is  a  yellow'  metal,  having  a  specific  gravity  of  2*54,  which  is  malleable, 
and  has  a  certain  amount  of  tenacity,  and  burns,  when  heated  in  the  air,  with 
a  crimson  flame  emitting  sparks.  It  decomposes  water.  The  only  oxide  is 
strontia  (SrO).  The  most  important  salt  is  strontic  nitrate  (Si2NO  ),  now 


BARIUM— -AL  UMINIUM. 


677 


used  extensively  in  all  pyrotechnic  displays  in  consequence  of  the  marked 
red  which  it  imparts  to  flame.  The  other  important  salts,  both  of  which 
occur  native,  are  strontic  carbonate  (SrC03),  and  strontic  sulphate  (SrS04). 


BARIUM. 

Symbol,  Ba.  Atomic  weight,  1 37. 

There  is  a  mineral  called  “  heavy  spar,”  containing  baryten,  so  called  from 
(heavy);  it  is  a  sulphate  of  barium  or  baric  sulphate  (BaSO«),  and  it 
has  given  the  name  to  this  metal.  Discovered,  like  the  preceding  ones  of  this 
class,  by  Davy,  in  1808. 

It  is  a  pale  yellow  metal,  the  specific  gravity  of  which  has  not  yet  been 
determined.  Barium  decomposes  water  and  is  quickly  oxidized  in  the  air. 
It  forms  two  oxides:  baryta  or  baric  oxide  (BaO),  and  baric  dioxide  or  per¬ 
oxide  ot  barium  (BaO*). 

The  chief  salts  are  baric  chloride  or  chloride  of  barium  (BaC2,  2H20),  baric 
sulphate  (BaS04),  which  occurs  native,  and  is  used  for  adulterating  white  lead, 
and  baric  nitrate  (Ba2N03),  used  in  common  with  the  baric  chloride  as  the 
chief  test  for  sulphates.  Baric  nitrate  is  likewise  employed  in  pyrotechnic 
mixtures  to  impart  a  green  colour  to  the  fire. 

Baric  carbonate  (BaCOs),  occurs  native,  and  is  called  withe  rite. 

The  metals  of  this  class  all  form  insoluble  carbonates,  oxalates,  sulphates, 
and  phosphates. 

- - — « - 


CLASS  III. 

ALUMINIUM,  GLUCINIUM,  ZIRCONIUM,  THORIUM,  YTTRIUM, 
ERBIUM,  CERIUM,  LANTHANUM,  DIDYMIUM. 

Metals  0/  the  Earths* 


ALUMINIUM. 

Symbol,  Al.  Atomic  weight,  27-5. 

Every  kind  of  clay  representing  compounds  of  aluminium  with  silica,  called 
scientifically  hydrated  aluminic  silicate,  whether  it  be  common  clay,  pipeclay, 
blue  clay,  loam,  or  firc-clav,  or  the  more  valuable  fomi  called  kaolin — the 
porcelain  clay  of  china,  or  Cornish  stone,  yellow  ochre,  red  bole,  fullers’  earth, 
— all  contain  this  metal. 

The  perfect  productions  of  S<5vr6s  are  said  to  be  made  of  a  composition 

consisting  of 


Washed  kaolin 

.  62  parts 

Aumont  sand 

•  •  1 7 

Quartz  or  feldspar  . 

•  *  *7  yj 

Bougival  chalk 

■  4  „ 

100 

*  Of  these,  aluminium  onlv  will  be  considered,  as  the  other  metals  of  this  class  do  not  present  features 

of  any  interest  to  the  general  reader. 


CHEMISTR  Y 


6'j  8 


The  first  step  in  the  preparation  of  aluminium  is  the  production  of  alum 
from  the  alum  schist  or  alum  ore  found  near  Glasgow  and  at  Whitby  in  York¬ 
shire;  indeed,  the  metal  is  so  called  from  (tinmen ,  clay,  and  was  discovered 
by  Davy  in  1808.  It  is,  however,  from  the  aluminium  chloride  or  chloride  of 
aluminium  (AbCl6)  that  the  metal  is  usually  procured. 

The  following  is  M.  St.  Claire  Deville’s  process  for  obtaining  this  metal: 

“  Introduce  into  a  glass  tube  of  about  an  inch  in  diameter  from  200  to  300 
grammes  of  chloride  of  aluminium,  closing  the  ends  with  a  plug  of  asbestos ; 


Fig.  512. — Se'vrcs  Porcelain,  French  Exhibition,  1867. 

then  conduct  hydrogen  gas,  dry  and  perfectly  free  from  atmospheric  air,  into 
the  tube,  and  heat  the  chloride  of  aluminium  in  this  current  of  gas  by  means 
of  charcoal.  I  his  will  have  the  effect  of  driving  off  the  hydrochloric  acid, 
chloride  of  silicium,  and  chloride  of  sulphur,  with  which  it  is  always  impreg¬ 
nated.  Capsules  of  as  large  size  as  possible,  containing  each  some  grammes 
of  sodium,  previously  crushed  between  two  sheets  of  dry  filter-paper,  are  then 
introduced  into  the  glass  tube.  The  tube  bein^  full  of  hydrogen,  the  sodium 
is  melted;  and  the  chloride  of  aluminiun,  on  being  heated,  will  be  distilled 
and  decomposed  with  incandescence,  which  may  be  easily  moderated.  The 
operation  will  be  complete  when  all  the  sodium  has  disappeared,  and  the 
chloride  of  sodium  formed  has  absorbed  a  sufficient  quantity  of  chloride  of 
aluminium  to  saturate  it.  The  aluminium  will  now  exist  in  the  state  of  a 
double  chloride  of  aluminium  and  sodium,  which  is  a  very  fusible  and  volatile 
compound.  I  he  capsules  are  next  to  be  removed  from  the  glass  tube,  and 
placed  in  a  large  porcelain  tube  furnished  with  a  pipe  leading  to  a  receiver. 
Ihrough  this  porcelain  tube,  while  heated  to  a  lively  red  heat,  a  current  of 
hydrogen,  dry  and  free  from  air,  is  caused  to  pass,  and  the  chloride  of  alumi- 


ALUMINIUM. 


679 


nium  and  sodium  will  be  thereby  distilled  without  decomposition,  and  collect 
in  the  receiver.  After  the  operation  all  the  aluminium  will  be  found  collected 
in  the  capsules  in  the  form  of  large  globules;  these  are  washed  in  water,  which 
will  carry  off  a  little  of  the  salt  produced  by  reaction,  and  also  some  brown 
silicium.  In  order  to  form  a  single  mass  of  all  these  globules,  after  being 
cleansed  and  dried  they  are  introduced  into  a  capsule  of  porcelain,  into  which 
is  put,  as  a  flux,  a  small  quantity  of  the  product  of  the  preceding  operation — 
i.e.,  of  the  double  chloride  of  aluminium  and  sodium.  On  heating  the  capsule 
in  a  muffle  to  the  temperature  of  about  the  melting-point  of  silver,  all  the  glo¬ 
bules  will  be  seen  to  unite  in  a  brilliant  mass,  which  is  allowed  to  cool,  and 
then  washed.  The  melted  metal  must  be  kept  in  a  closed  porcelain  crucible 
until  the  vapours  of  the  chloride  of  aluminium  and  sodium  with  which  the 
metal  is  impregnated  have  entirely  disappeared.  The  metallic  mass  will  then 
be  found  surrounded  by  a  light  pellicle  of  alumina  arising  from  the  oartial  de¬ 
composition  of  the  flux.” 

Messrs.  Bell,  of  Newcastle,  have  perfected  a  convenient  process,  which 
works  very  admirably.  They  heat  in  a  reverberatory  furnace  the  double  salt 
the  sodio-aluminic  chloride  (NaCl,AlCl3)  with  fluorspar  or  cryolite  and  metallic 
sodium  ;  a  very  powerful  action  occurs,  and  large  quantities  of  aluminium  are 

obtained. 

Aluminium  is  a  white  metal,  very  much  like  zinc,  and  is  malleable  and  duc¬ 
tile  :  it  can  be  rolled  into  sheets  or  drawn  into  wire,  and,  when  cast  into  long 
bars  and  struck  with  a  wooden  rod,  is  very  sonorous,  the  vibrations  continuing 
for  a  considerable  length  of  time  after  the  blow  is  given. 

Aluminium  is  remarkably  light,  having  a  specific  gravity  of  only  2  6,  so  that 
it  is  rather  more  than  two-and-a-half  times  heavier  than  water,  and  is  there¬ 
fore  used  for  a  great  variety  of  useful  and  ornamental  purposes  where  light¬ 
ness  is  desirable. 

The  only  oxide  known  is  alumina  (A1*03),  the  basis  of  all  clays,  which  in  the 
native  crystalline  state  is  known  in  the  form  of  corandum  and  emery,  or  the 
costly  jewels,  the  ruby  and  sapphire.  The  specific  gravity  of  the  ruby  is  3*95. 

Alumina  is  one  of  the  most  valuable  mordants  known  in  the  arts  of  dyeing 
and  calico  printing. 

The  most  important  salts  of  aluminium  are  aluminic  chloride  (A12C16), 
aluminic  sulphate  (AI.3SO4,  18FFO),  and  alum  or  potassio-aluminic  sulphate 
(KALSO4,  i2HaO).  There  are  other  varieties  of  alum  obtained  by  substituting 
for  the  one  atom  of  potassium  an  equivalent  of  sodium  or  ammonium;  and 
if  iron,  chromium,  or  manganese  are  substituted  for  the  aluminium,  what  is 
termed  iron,  chrome,  and  manganese  alums  are  produced,  <?f  which  one  ex¬ 
ample  may  suffice, — iron  alum  (KFe*S04,  I2H30).  Lr.  this  it  will  bi  noticed 
that  Fe3S04  is  substituted  for  AhSO*. 


68o 


CHEMJSTR  Y. 


CLASS  IV. 

MAGNESIUM,  ZINC,  CADMIUM. 
The  Zinc  Class. 


MAGNESIUM. 

Symbol,  Mg  Atomic  weight,  24C3. 

Sea-water,  many  springs,  but  especially  the  mountain  limestone  or  dolomite 
is  to  be  regarded  as  the  chief  source  of  magnesium,  so  called  because  it  was 
originally  brought  from  Magnesia  in  Asia  Minor.  Magnesium  has  assumed  an 
important  position  amongst  the  metals  on  account  of  its  useful  employment 
as  a  means  of  producing  a  brilliant  artificial  light.  The  manufacture  and  the 
uses  of  the  metal  have  been  so  lately  described  in  the  “  Mechanic’s  Magazine,”* 
that  extracts  from  this  thoroughly  practical  thesis  will  be  given  here. 

“Magnesium  was  one  of  Sir  Humphrey  Davy’s  many  discoveries.  He 
proved,  in  1808,  with  the  galvanic  battery  of  the  Royal  Society,  that  magnesia 
was  a  compound  of  a  metal  with  oxygen, — in  a  word,  was  the  ash  of  a  burnt 
metal.  The  fact  lay  dormant  for  many  years  :  a  new  entry  was  simply  made 
in  the  catalogue  of  elements.  Bussy,  the  Paris  chemist,  exhibited,  about  1830, 
the  metal  in  larger  quantities  than  had  yet  been  obtained :  he  treated  mag¬ 
nesium  chloride  with  potassium,  when  the  potassium,  combining  with  the 
chlorine,  left  the  magnesium  in  the  metallic  state.  There  discovery  again 
rested  until  about  1856,  when  Deville  and  Caron  taught  chemists  howto  pro¬ 
cure  the  metal  with  greater  ease  by  substituting  sodium  for  potassium.  Bun¬ 
sen,  of  Heidelberg,  and  Roscoe,  of  Manchester,  shortly  after  proclaimed  its 
value  as  a  source  of  light.  Thus  science  did  her  work:  it  remained  for  prac¬ 
tical  skill  to  coin  her  hints  into  current  commercial  service.  The  matter  was 
taken  up  at  this  point  by  Mr.  Edward  Sonstadt,  a  young  Englishman  with  a 
name  derived  from  Swedish  ancestry.  Why,  he  asked,  should  not  the  labo¬ 
ratory  process  of  Deville  and  Caron  be  so  far  improved  as  to  be  capable  of 
being  worked  on  a  large  manufacturing  scale  ?  and  resolved  to  devote  his 
energies  to  the  solution  of  the  question.  Happily,  he  succeeded.  After  up¬ 
wards  of  a  year’s  experimenting,  he  pursuaded  some  gentlemen  to  join  him; 
a  Company  for  the  production  of  magnesium  was  formed,  and  business  com¬ 
menced  in  Manchester.  The  metallurgical  process  conducted  on  the  Com¬ 
pany’s  premises  in  Springfield  Lane,  Salford,  is  as  follows : 

“  Lumps  of  rock  magnesia  (carbonate  of  magnesia)  are  placed  in  large  jars, 
into  which  hydrochloric  acid  in  aqueous  solution  is  poured.  Chemical  action 
at  once  ensues  :  the  chlorine  and  the  magnesium  embrace,  and  the  oxygen 
and  carbon  pass  off  in  the  form  of  carbonic  acid.  The  result  is  magnesium 
in  combination  with  chlorine  instead  of  with  oxygen.  The  problem  now  is  to 
dissolve  this  new  alliance, — to  get  rid  of  the  chlorine,  and  so  obtain  the  mag¬ 
nesium.  First  the  water  must  be  evaporated,  which  would  be  easy  enough  if 
not  attended  with  a  peculiar  danger.  To  get  the  magnesium  chloride  perfectly 
dry,  it  is  necessary  to  bring  it  to  a  red  heat ;  but  this  would  result  in  the  metal 


August  30,  1867. 


MAGNESIUM. 


(>S  i 


Fig.  51 3. — Magnesium  Balloons  at  the  Crystal  Palace. 


dropping  its  novel  acquaintance  with  chlorine  and  resuming  its  ancient  union 
with  oxygen.  To  avert  this  re-combination,  the  magnesium  chloride,  whilst 
yet  in  solution,  is  mixed  with  sodium  chloride  (i.e.,  common  salt'  or  potassium 
chloride,  and,  thus  fortified,  the  aggressions  of  oxygen  whilst  drying  are  kept 
off.  The  mixture  is  exposed  in  broad  open  pans  over  stoves,  and  when  suffi¬ 
ciently  dry  the  double  salt  is  scraped  together  and  placed  in  an  iron  ciucible, 
in  which  it  is  heated  until  melted,  whereby  the  last  traces  of  water  are  arixen 
off;  it  is  then  stowed  away  until  required  in  air-tight  vessels  to  prevent  deli¬ 
quescence.  Here  comes  in  that  curious  metal,  sodium,  also  discovered  by 

Davy.  , .  -  j  T1  • 

“Having,  then.,  got  together  sodium  and  dry  magnesium  chlonde,  all  is 
ready  for  the  production  of  the  desired  metal,  f  ive  parts  of  the  magnesium 
chloride  (mixed, however,  as  we  have  noted,  with  sodium  chloride)  to  one  part 
of  sodium,  are  depos  ted  in  a  strong  iron  crucible  with  a  closely-fitting  lid, 
which  is  screwed  down.  The  crucible  is  placed  in  a  furnace  and  heated  to 
redness.  The  contents  are  thus  fused  together,  when  the  sodium  takes  the 
chlorine  from  the  magnesium.  The  crucible  is  then  lifted  from  the  hre  and 
allowed  to  cool.  When  the  lid  is  removed,  a  solid  mass  is  discovered,  which, 
when  tumbled  out  and  broken  up,  reveals  magnesium  in  nuggets  of  various 
sizes  and  shapes,  bright  as  silver,  and  like  eggs,  buttons,  nuts,  an  pm  "-'at  s, 
and  also  in  minute  granules  and  black  powder;  all  w  hich  is  care  u  \  sepa  a  cc 
and  collected  from  the  dross.  The  magnesium  in  this  condition  contains 
various  impurities,  the  worst  of  which  is  uncomb.ned  sodium.  From  these * 
is  delivered  by  distillation.  The  crude  metal  is  placed  in  a  crucible,  through 
the  bottom  of  which  a  tube  ascends  to  within  an  inch  of  the  I'd ;  the  tube 
leads  to  an  iron  box  placed  beneath  the  bars  of  the  furnace,  so  that  it  may  be 
kept  cool.  The  lid  bein^  carefully  fixed,  the  atmospheric  air,  as  containing 


682 


CHEMISTR  Y 


oxygen,  is  expelled  by  the  injection  of  hydrogen,  and  as  the  crucible  becomes 
heated  the  magnesium  rises  in  vapour,  descends  the  upright  central  tube,  and 
condenses  in  purity  in  the  box  below;  it  is  subsequently  melted  and  cast  in 
ingots. 

“  When  the  Magnesium  Company  commenced  business,  it  was  fancied  that 
their  product  might  be  used  in  jewellery,  but  a  little  experience  dissipated  the 
illusion.  A  fresh  surface  of  magnesium  is  little  inferior  in  appearance  to 
silver;  but  it  soon  contracts  from  the  dampness  of  the  atmosphere  a  coat  of 
oxide,  which  is  fatal  to  its  beauty.  Gradually  the  Company  were  brought  to 
the  conclusion  that  they  must  find  their  market  in  the  use  of  the  metal  as  a 
source  of  light.  For  this  their  commodity  had  high  qualifications.  Its  power 
was  unequalled  save  by  the  electric  light,  and  it  has  a  peculiar  charm  in  dis¬ 
playing  colours  as  in  sunshine. 

“At  the  meeting  of  the  British  Association  in  Nottingham,  Mr.  Larkin 
lighted  up  the  large  refreshment-tent,  including  a  temporary  garden,  for  two 
evenings  with  a  couple  of  his  lamps,  and  obviated  the  necessity  of  laying  on 
gas;  and  his  invention  has  since  been  exhibited  and  tested  on  several  similar 
important  occasions.  He  has  also  devised  a  portable  lamp  for  surveyors  of 
mines  and  explorers  of  subterranean  and  dark  places,  which  received  the 
approval  of  practical  men.  We  are  as  yet  at  the  beginning  of  the  uses  of  the 
magnesium  light :  its  only  real  rival  in  illuminating  power  is  electricity,  which, 
however,  is  not  likely  to  compete  with  it  on  the  score  of  handiness  and  porta¬ 
bility.  It  is  true,  magnesium  is  at  present  a  costly  material:  it  is  retailed  in 
powder  at  $s.  per  oz. — the  price  of  silver ;  though,  it  is  to  be  noted,  an  ounce 
of  magnesium  is  six  times  the  bulk  of  an  ounce  of  silver.  Moreover,  the  manu¬ 
facturers  assure  us  that  as  the  consumption  increases  the  price  will  fall.  Pro¬ 
bably  some  chemist  will  find  out  how  to  dispense  with  sodium  in  extracting  it 
from  the  ore,  or  else  how  to  obtain  sodium  more  cheaply.  The  price  of  mag¬ 
nesium  is  ruled  by  that  of  sodium:  all  else  connected  with  its  working  is  ot 
comparatively  small  importance.  The  qualities  and  merits  of  the  magnesium 
light  are  now  familiar  to  most  people :  these  have  been  displayed  with  great 
effect  by  means  of  the  balloons  sent  up  from  the  Crystal  Palace,  with  rockets 
attached  primed  with  magnesium  filings  and  chlorate  of  potash.  The  rockets, 
as  they  burn,  illuminate  the  palace  and  the  surrounding  country  with  a  radiance 
between  sunshine  and  moonshine,  and  display  the  countenances  and  dresses 
of  the  gazing  crowd,  and  the  flowers  and  foliage  of  the  garden,  in  the  tints  of 
daylight.  For  fireworks  magnesium  serves  as  an  ingredient  of  surpassing 
brilliancy;  the  makers,  however,  complain  that  its  very  excellence  is  an  ob¬ 
jection,  for  those  who  see  it  once  demand  it  always,  to  the  prejudice  of  the 
commoner  and  less  costly  articles.” 

There  is  only  one  oxide  ot  magnesium,  viz.,  magnesia  (MgO). 

The  important  salts  of  this  metal  are  magnesic  chloride  (MgCl2),  the  source 
of  the  metal,  magnesic  sulphate  or  Epsom  salts  (MgS04,  7H20),  and  mag¬ 
nesic  carbonate  (MgC03). 

The  magnesic  silicates  occur  in  nature,  some  of  the  most  familiar  being 
talc  (4MgO,  5S,02),  steatite,  French  chalk  or  soapstone,  and  meerschaum,  or 
hydrated  silicate  of  magnesia. 

The  phosphates  of  magnesium  are  important  in  analytical  chemistry,  the 
ammonio-magnesic  phosphate  (MgH4N,  P04,  6H20)  being  the  product  ob¬ 
tained  when  solution  of  hydro-disodic  phosphate,  mixed  with  that  of  ammo¬ 
nium  chloride,  is  added  to  one  of  a  magnesic  salt. 


7JNC. 


683 


ZINC. 

Symbol,  Zn.  Atomic  weight,  65'2. 

This  metal,  it  is  stated  by  Griffiths,  “  was  first  thus  called  in  the  writings  of 
Paracelsus,  about  the  year  1 540.  The  term  is  probably  derived  from  the 
German  word  zinken ,  signifying  ‘  nails,’  and  applied  to  this  metal  on  account 
of  its  frequently  forming  pointed  particles  somewhat  resembling  nails  when 
melted  and  suddenly  poured  into  water.” 


Fig.  514. — Zinc  Casting ,  French  Exhibition ,  1867. 


Sources  whence  Derived. 

It  is  obtained  from  the  mines  of  Cornwall,  Wales,  Cumberland,  and  the 
Isle  of  Man,  in  the  form  of  zincic  sulphide  (Blende  or  Black  Jack),  and  zincic 
carbonate  or  calamine;  is  very  abundant  in  England,  and  is  found  prinapu 
in  the  Mendip  Hills  and  various  parts  of  Somersetshire,  at  Holywell,  Hint- 
shire,  at  Castleton,  Derbyshire,  and  in  Cumberland.  , 

in  order  to  reduce  the  zincic  sulphide  or  carbonate  to  the  metallic  state,  t  ic 
powdered  ore  is  roasted  or  calcined,  by  which  it  loses  about  20  per  cent.,  ant 
is  converted  into  an  oxide.  It  is  then  ground  in  a  mill,  and  mixed  with  pow¬ 
dered  coal,  and  strongly  heated  in  large  clay  crucibles,  so  that,  as  the  vapour 
of  zinc  is  produced,  it  is  distilled  per  descensum,  and  is  condensed  partly  in 
powder  and  partly  in  irregular-shaped  lumps,  which  fall  into  iron  basins  placed 
at  the  end  of  the  pipe:  this  is  constantly  looked  to,  to  prevent  the  zinc  that 
distils  over  clogging  it  up.  The  crude  metal  is  again  melted  and  cast  into 

ingots  or  sheets 


684 


CHEMISTRY. 


Physical  Properties. 

Zinc  presents  a  beautiful  crystalline  structure  if  a  thick  bar  or  slab  is  broken 
with  a  sledge-hammer;  its  colour  is  a  bluish-white.  In  bending  zinc  for 
battery  purposes,  it  is  soon  found  that  if  the  metal  is  heated  to  about  300°  F., 
it  is  much  more  manageable  and  does  not  break,  and  thus  in  rolling  the  zinc 
the  slabs  are  always  previously  heated  to  21 2°  or  300°;  at  a  higher  tempera¬ 
ture  it  again  becomes  brittle,  and  melts  at  77 30  F. 

The  specific  gravity  of  zinc  is  6‘8  to  7*1.  The  “  Building  News,”  speaking 
with  authority  on  the  application  of  this  metal  to  building  and  other  purposes, 
says : 

“  This  metal  has  been  largely  employed  for  pipes,  for  galvanic  batteries  used 
,n  working  the  electric  telegraph,  as  a  substitute  for  white  lead,  and  as  a  con¬ 
stituent  of  brass  and  German  silver. 

“  Zinc  is,  as  is  well  known,  largely  obtained  from  Prussia ;  and  we  find  that 
nearly  4,500,000  cwt.  of  zinc  were  obtained  in  1857.  In  the  seven  large  smelt¬ 
ing  establishments  in  Belgium  and  Prussia,  belonging  to  the  Vieille  Montagne 
Company,  there  are  230  furnaces.  Fifteen  years  ago  the  quantity  of  zinc  used 
for  roofing  was  not  more  than  5,000  tons  ;  now,  it  appears,  23,000  tons  of  sheet 
zinc  are  annually  made  by  this  Company.  For  ship  sheathing  3,500  tons  are 
produced,  although  fifteen  years  ago  zinc  was  not  employed  at  all  for  this 
purpose.  Stamped  ornaments  in  zinc  date  only  from  1852;  now  there  are 
1,500  tons  produced  for  this  object.  For  ships’  sheathing  zinc  must  neces¬ 
sarily  be  altogether  free  from  impurity,  or  it  will  soon  decay.  But  there  can 
be  no  question  about  the  usefulness  of  this  metal  for  budding  purposes;  and 
the  fact  that  it  is  coming  into  still  greater  use  and  is  becoming  better  known 
and  appreciated  is  evidence  that  its  reputation  is  increasing.  With  care  in 
purchasing  and  laying  there  is  but  little  doubt  that  it  will  turn  out  well.  In 
Paris  it  has  been  used  for  nearly  every  roof  formed  for  some  years.  The  new 
markets,  constructed  of  iron  in  1856,  have  been  covered  with  zinc,  and,  except¬ 
ing  in  one  place  where  the  workmen  were  careless,  the  whole  of  the  zinc  is  in 
capital  condition.  In  Germany  zinc  for  roofing  is  largely  used,  and  the  work 
is  generally  remarkable  for  solidity  and  closeness.” 

Chemical  Properties. 

At  a  bright  red  heat  and  when  exposed  to  the  air  zinc  is  t apidly  oxidized, 
and  then  takes  fire,  burning  with  a  bright  greenish  flame,  and  forming  the  only 
oxide  of  this  metal,  viz.,  the  zincic  oxide  (ZnO),  or  what  was  formerly  called 
the  “  flos  philosophorum  ”  or  philosopher’s  wool,  and  now  termed  zinc  white. 

The  chief  salts  of  zinc  are  zincic  sulphate  (ZnS04,  7H0O),  also  zincic  chlor¬ 
ide  (ZnCl2),  used  as  a  disinfectant  under  the  name  of  “  Burnett’s  Disinfecting 
Fluid.”  Zincic  sulphide  or  blende  (ZnS)  and  zincic  carbonate  or  calamine 
(ZnC03)  have  already  been  spoken  of  as  the  natural  compounds  from  which 
zinc  is  obtained. 

- - + - - 

CADMIUM. 

Symbol,  Cd.  Atomic  weight,  112. 

This  metal  was  discovered  in  the  ore  of  zinc  by  Stromeyer  in  1817.  It  has 
as  pecific  gravity  of  8‘6,  is  a  white  metal  which  fuses  at  4420,  and  crystallizes 
in  octohedral  crystals. 


IRON. 


685 


Cadmic  oxide  or  oxide  of  cadmium  (CdO)  is  the  only  known  oxide  of  this 
metal.  Cadmic  sulphide,  chloride,  and  iodide  are  well-known  salts  of  cad¬ 
mium.  1  he  last-named,  iodide,  has  already  been  mentioned  in  connection 
with  the  photographic  art. 


CLASS  V. 

IRON,  MANGANESE,  COBALT,  NICKEL,  CHROMIUM, 
URANIUM,  INDIUM. 

The  Iron  Class. 


IRON. 

Symbol,  Fe  (Ferrum).  Atomic  weight,  56. 

Sources  whence  Derived. 

In  an  orbit  peculiar  to  themselves  are  supposed  to  revolve  countless  frag¬ 
ments  of  a  solid  nature,  varying  in  weight  from  tons  to  pounds,  ounces,  and 
grains  or  mere  dust:  these  bodies  are  called  asteroids  or  planetary  dust;  and 
when  they  enter  the  atmosphere  of  the  earth,  they  become  ignited  by  friction 
in  their  very  rapid  movement  through  the  upper  portions  of  the  air,  and,  when 
drawn  within  the  sphere  of  the  attraction  of  the  earth,  they  fall  into  or  upon 
our  planet,  and  are  then  called  “  meteorites.'’  These  remarkable  visitors  con¬ 
tain  a  large  proportion  of  pure  metallic  iron,  also  sulphur,  phosphorus,  carbon, 
manganese,  magnesium,  nickel,  cobalt,  tin,  and  copper. 

Metallic  iron  in  small  quantities  has  been  found  associated  with  the  ores  of 
platinum.  The  orec  of  this  metal  are,  however,  legion,  and  amongst  the  most 
important  are  iron  pyrites  (FeS2);  clay  ironstone,  an  impure  carbonate,  and 
the  source  of  nearly  all  the  enormous  quantities  of  iron  made  in  Great  Britain; 
the  haematites,  red  and  brown  (the  former  Fe203,  the  latter  2Fe203,  sHaO); 
specular  iron  ore  (also  Fe*03) ;  and  the  magnetic  iron  ore  or  loadstone  (FeO, 

Fa°3). 

The  smelting  of  iron  ore  is  a  process  which  has  been  brought  to  the  highest 
degree  of  perfection  in  this  country ;  it  is,  therefore,  interesting  to  notice  first 
the  more  p:imitive  and  ancient  method  of  reducing  iron  ore  to  the  metallic 
state,  such  as  that  illustrated  in  Fig.  515,  and  carried  on  by  the  natives  in 
India. 

"•Smelting  of  Iron  Ore  in  Kasya  Hills  —  The  following  is  the  method  pur¬ 
sued  from  time  immemorial  by  the  natives  of  this  part  of  the  country  in 
working  down  the  ores  of  iron  so  plentifully  met  with  hereby.  '1  here  are  large 
grass  huts  at  least  25  ft.  high,  the  thatch  of  which  reaches  down  to  the  ground 
on  all  sides;  the  interior,  of  an  oval  form,  15  by  30  ft.  in  the  two  diameters,  is 
divided  into  three  apartments,  the  central  one  being  the  smelting-room.  I  wo 
large  double  bellows,  with  the  nozzles  pointed  downwards,  are  set  up  on  one 
side  of  the  apartment,  on  the  upper  side  of  which  a  man  stands  with  one  foot 
on  each,  his  back  supported  by  two  planks.  He  holds  a  stick  in  his  left  hand, 
which  is  suspended  from  the  roof,  and  has  two  straps  attached  to  it  below, 
connected  with  the  two  bellows:  these  are  worked  quickly  by  a  wriggling  mo¬ 
tion  of  the  loins  and  the  strength  of  the  leg.  1  he  nozzles  of  the  bellows  unite 
in  a  tube  which  leads  underground,  from  a  sort  of  wind-chest,  to  the  hearth, 


686 


CHEMFSTR  V. 


FIG.  515. — Smelting  Iron  Ore  in  India. 


about  four  feet  in  front  of  them.  Over  the  hearth  is  a  chimney  of  pipeclay, 
braced  with  iron  hoops,  2  ft.  in  diameter  at  the  bottom  and  about  6  ft.  high ; 
the  mouth  at  the  bottom  is  on  the  side  away  from  the  bellows,  and  the  chim¬ 
ney  inclined  from  them,  to  direct  the  heated  air  from  the  smelter  towards  an 
opening  in  the  roof.  At  the  right  side  of  the  bellows,  and  even  with  the  top 
of  the  chimney,  is  a  trough  containing  ciamp  charcoal  and  ironsand.  At  every 
motion  of  his  body  the  operator  with  a  long  spoon  tumbles  a  piece  of  this  char¬ 
coal,  with  the  ironsand  adhering  to  it,  down  the  funnel  of  the  furnace;  and 
when  a  mass  of  melted  or  rather  softened — iron  is  formed  on  the  hearth,  it  is 


IRON. 


687 


taken  out  with  the  tongs,  and  beaten  with  a  heavy  wooden  mallet  on  a  large 
stone  by  way  of  anvil.  The  iron  in  this  state  is  sent  down  to  the  plains  for 
sale  or  barter.”* 

Herodotus  tells  us  that  amongst  the  most  precious  gifts  presented  by  the 
Indian  monarch  Porus  to  Alexander  the  Great  was  a  pound  of  steel,  the  value 
of  which  at  that  period,  according  to  a  rough  calculation  of  the  elder  Mushet, 
may  be  estimated  at  about  ,£40.  A  pound  of  steel,  at  present  prices  of  ^14  a 
ton,  costs,  within  a  fraction,  three-halfpence  of  our  money.  That  the  manu¬ 
facture  of  steel  was  in  later  ages  carried  to  great  perfection  in  India,  as  well 
as  in  the  South  of  Europe,  especially  in  its  application  to  warlike  instruments, 
as  swords,  spear-heads,  daggers,  and  the  like,  we  have  abundant  evidence  in 
specimens  of  ancient  art. 

In  commerce  iron  is  known  and  used  in  three  different  conditions,  viz.,  cast 
iron,  wrought  iron,  and  steel.  Each  of  these  forms  exhibits  special  physical 
properties,  and  all  differ  essentially  in  their  chemical  constitution. 

As  a  contrast  to  the  ancient  method  of  smelting  iron  ore  in  India,  we  have 
in  England  the  immense  “blast  furnace,”  50  It.  high  and  from  14  to  17  ft. 
in  diameter.  The  crude  materials  are  roasted  clay  ironstone,  coal,  and  lime¬ 
stone:  these,  with  the  assistance  of  a  powerful  blast  of  air,  react  on  each 
other:  the  carbon  deoxidizes  the  oxide  of  iron,  and  the  limestone  is  the  flux 
which  melts  with  and  carries  oft"  the  earthy  matter.  The  iron  falls  down  and 
collects  in  what  is  called  the  crucible  or  hearth,  and  is  run  into  rough  sand 
moulds,  and  when  cold  is  called  “pig”  or  “cast”  iron. 

By  the  last  official  returns,  taken  from  Hunt,  the  total  quantity  of  iron  ore 
raised  in  the  United  Kingdom,  in  1867,  amounted  to  10,021,058  tons  9  cwt., 
the  estimated  value  of  which  was  ^3,2 10,098  o.r.  4//.  foreign  ores  imported, 
86,568  tons.  Total  quantity  of  iron  ore  converted  into  pig  iron,  10,107,626 
tons.  The  number  of  furnaces  in  blast  were  55 1  L 


Pig  iron  produced : 
In  England 
„  Wales  . 

„  Scotland 


Total  production  of  pig  iron  in  Great  Britain 

This  quantity,  estimated  at  the  mean  average  cost  at  the  place  of  production, 
would  have  a  value  of  ,£11,902,557.  Into  this  large  amount  of  ore  North- 
amptonshire  enters  for  416,765  tons,  of  the  estimated  value  of  ^104, 191  ;  and 
the  North  Riding  of  Yorkshire,  or  the  Cleveland  district,  produced  2,739,033 
tons,  of  the  estimated  value  of  ,£798.056.  The  total  produce  of  iron  ore 
in  Scotland  in  the  same  year  was  1,264,800  tons,  of  the  estimated  value  of 
^£31 1,200,  both  returns  being  less  than  the  corresponding  returns  of  the  pre¬ 
ceding  year.  Such  are  the  most  recent  returns  of  a  manufacture  which  gives 
direct°  employment  to  250,000  persons,  and  the  prosperity  of  which,  or  the 
reverse,  affects  the  comforts  or  privations  of  so  many  thousands  ot  our  fellovv- 


Tons. 

2,810,946^ 

919,077 

1,031,000 


4,76 1, 02  3^ 


countrymen.  ,  ,  .  .  .  ,  ... 

Pig  or  crude  cast  iron  contains  many  foreign  bodies  which  interfere  with  its 
use  for  purposes  where  tough,  good  iron  i^  required.  1  here  are  three  varieties 
of  cast  iron,  viz.,  grey,  mottled,  and  white  cast  iron.  I  hey  contain  combined 


*  "‘Journal  of  the  Asiatic  Society,”  Vol.  I.  183 J. 


688 


CHEMISTR  Y 


carbon,  graphite  diffused  through  the  metal,  silicon,  sulphur,  phosphorus,  iron, 
manganese,  and  sometimes,  though  rarely,  copper,  arsenic,  cobalt,  and  chro¬ 
mium.  To  free  the  iron  from  these  impurities,  Mr.  Cort  invented  and  carried 
out  the  process  of  “puddling”  iron,  by  which  the  carbon  and  other  bodies 
were  almost  wholly  taken  out  of  the  pig  iron,  and  “  wrought  ”  or  nearly  pure 
iron  obtained. 

To  convert  wrought  iron  into  steel,  the  carbon  is  again  united  by  the  tedious 
and  costly  process  called  “cementation,”  the  “bar”  or  “wrought”  iron  being 
kept  for  some  three  weeks  in  a  furnace  surrounded  with  charcoal,  until  it  has 
absorbed  a  sufficient  quantity  of  solid  carbon. 

The  most  remarkable  improvement  in  the  manufacture  of  pig  iron  direct 
into  wrought  iron  or  into  steel  is  undoubtedly  that  of  Mr.  Bessemer.  The 
author  of  a  very  clever  pamphlet  on  “  Heaton’s  Process  for  the  Treatment  of 
Cast  Iron  in  the  Manufacture  of  Steel”  (to  be  described  presently),  thus 
speaks  of  it : 

“  The  enthusiasm  with  which  the  Bessemer  process  was  welcomed  in  all 
parts  of  the  world,  in  the  year  1855,  is  still  fresh  in  the  recollection  of  all  taking 
an  interest  in  the  iron  trade.  The  invention  excited  a  kind  of  frenzy.  The 
very  site  where  the  experiments  had  been  carried  on  derived  fresh  interest 
from  the  event.  On  the  spot  where  Richard  Baxter  tried  to  save  men’s  souls 
from  fire  eternal,  Bessemer  had  studied  as  earnestly  to  save  their  bodies  from 
fire  temporal.  The  “heel-piece”  for  the  “limping  sinner”  was  replaced  by  the 
crucible  for  the  sweating  puddler.  The  making  of  iron  bars,  up  to  that  time 
an  operation  of  four  successive  fires,  was  now  performed  by  one  heat.  After 
the  melted  iron  had  run  out  of  the  pig-producing  furnace,  the  usual  process 
had  been  to  stir  it  by  human  labour,  with  a  view  to  expose  all  parts  of  its 
interior  and  exterior  to  the  action  of  the  atmosphere,  in  order  that  the  carbon, 
and  other  extraneous  matter,  might  be  burnt  out  by  the  aid  of  oxygen.  Mr. 
Bessemer  substituted  for  this  the  forcing  of  air  by  steam  power  through  the 
molten  metal.  Thus,  without  any  additional  fuel  in  the  furnace,  the  heat  of 
the  iron  was  not  only  kept  up,  but  increased  by  the  combustion  of  the  oxygen 
mixing  with  the  carbon  in  the  interior  of  the  molten  metal,  and  the  iron  was 
rendered  malleable,  ready  for  the  tilt-hammer,  at  a  single  heat.” 

After  burning  out  the  carbon  and  silicon  from  the  pig  iron — usually  Lanca¬ 
shire  haematite  pig — the  Bessemer  steel  is  made  by  adding  to  the  melted 
wrought  iron  such  a  quantity  of  pure  cast  iron  as  is  necessary  to  give  carbon 
enough  to  convert  the  whole  mass  into  steel.  The  cast  iron  added  usually 
contains  6  per  cent,  of  carbon  and  10  of  manganese,  and  directly  after  it  is 
added  the  steel  is  cast  into  ingots.  Moreover,  the  whole  process  is  carefully 
watched  with  the  spectroscope,  so  that  the  person  who  directs  the  operations 
knows  exactly,  by  the  lines  obtained  from  the  flame  of  the  furnace,  when  the 
carbon  and  silicon  are  burnt  out,  and  the  precise  moment  when  the  pure  cast 
iron  should  be  added.  In  this  manner  six  tons  of  cast  iron  are  converted  into 
steel  in  twenty  minutes. 

It  would  be  thought  that  such  a  process  could  not  be  surpassed;  but  the 
author  of  the  pamphlet  already  referred  to  thus  speaks  of  the  rival  process 
described  by  Mr.  Heaton: 

“It  is  at  the  Langley  Mill  Steel  Works  that  Mr.  Heaton  has  successfully 
developed  the  process  which  he  has  patented,  which  is  one  remarkably  simple 
in  practical  working. 

“An  ordinary  cupola  furnace  is  charged  with  pig  iron  and  coke,  and  fired 


IRON. 


689 


in  the  usual  way,  and  the  iron  when  melted  is  drawn  off  into  a  ladle,  from 
which  it  is  transferred  to  the  converter. 

“The  converter  is  a  wrought-iron  pot  lined  with  fire-brick.  In  the  bottom 
is  introduced  a  charge  of  crude  nitrate  of  soda,  usually  in  the  proportion  of 
2  cwt.  per  ton  of  converted  steel,  usually  but  not  invariably  diluted  with  about 
25  lbs.  of  siliceous  sand.  This  charge  is  protected  or  covered  over  with  a  close- 
fitting  perforated  iron  plate  weighing  about  100  lbs.,  the  diameter  of  the  plate 
being  about  2  ft.  The  converter,  with  its  contents,  is  then  securely  attached, 
by  movable  iron  clamps,  to  the  open  mouth  of  a  sheet-iron  chimnev,  also  lined 
for  6  ft.  with  fire-brick,  and  the  melted  iron,  taken  in  a  crane  ladle  from  the 
cupola,  is  poured  in.  The  suosequent  part  of  the  process  is  thus  described  by 
Professor  Miller,  of  King’s  College,  Vice-President  of  the  Royal  Society  and 
Assayer  to  the  Mint. 

“‘In  about  two  minutes,’  writes  the  Professor  in  his  preliminary  report, 
dated  the  14th  of  October,  ‘a  reaction  commenced.  At  first  a  moderate 
quantity  of  brown  nitrous  fumes  escaped ;  these  were  followed  by  copious 
blackish,  then  grey,  then  whitish  fumes,  produced  by  the  escape  of  steam, 
carrying  with  it  in  suspension  a  portion  of  the  flux.  After  the  lapse  of  five  or 
six  minutes,  a  violent  deflagration  occurred,  attended  with  a  loud  roaring  noise 
and  a  burst  of  a  brilliant  yellow  flame  from  the  top  of  the  chimney.  This  lasted 
for  about  i§  minutes,  and  then  subsided  as  rapidly  as  it  commenced.  \\  hen 
all  had  become  tranquil,  the  converter  was  detached  from  the  chimney,  and  its 
contents  were  emptied  on  to  the  iron  pavement  of  the  foundry. 

“‘The  crude  steel  was  in  a  pasty  state  and  the  slag  fluid;  the  cast-iron 
perforated  plate,  which  was  placed  as  a  cover  to  the  converter,  had  become 
melted  up  and  incorporated  with  the  charge  of  molten  metal.  I  he  slag  had 
a  glassy  or  blebby  appearance,  and  a  dark  or  green  colour  in  mass.’ 

“  Professor  Miller  proceeds  to  detail  the  subsequent  parts  of  the  process, 
and  the  results  of  his  analysis  of  some  of  the  products. 

“‘A  mass  of  crude  steel  from  the  converter  was  then  subjected  to  the 
hammer.  About  4^  cwt.  of  the  crude  steel  was  transferred  to  an  empty  but 
hot  reverberatory  furnace,  where  in  about  an  hour’s  time  it  was  converted  into 
four  blooms,  each  of  which  was  hammered,  rolled  into  square  bars,  cut  up, 
passed  through  a  heating  furnace,  and  rolled  into  rod,  varying  in  thickness 
from  1  in.  to  five-eighths  of  an  inch. 

“‘Three  or  four  cwt.  of  the  crude  steel  from  the  converter  was  transfened 
to  a  re-heating  furnace,  then  hammered  into  flat  cakes,  which,  when  cold,  weic 
broken  up  and  sorted  by  hand  for  the  steel  melter. 

“  ‘  Two  fire-clay  pots,  charged  with  a  little  clean  sand,  were  heated,  and  into 
each  42  lbs.  of  the  cake  steel  was  charged ;  in  about  six  hours  the  melted  metal 

was  cast  into  an  ingot.  .  . 

“Two  other  similar  pots  were  charged  with  35  lbs.  of  the  same  cuke  steel, 
7  lbs.  of  scrap  steel,  and  1  oz.  of  oxide  of  manganese.  These  also  were  poured 
into  ingots.  The  steel  was  subsequently  tilted,  but  was  softer  than  was 

“‘These  results  on  the  whole  are  to  be  considered  rather  as  experimental 
than  as  average  working  samples.  I  have,  therefore,  made  an  t  x.imin.ition 
of  the  following  samples  only:  No.  4,  Crude  Cupola  I  ig,  1  °-  7*  1,1111  c  Lt 

Crude  Steel;  No.  8,  Rolled  Steely  Iron;  No.  5,  Slag  from  the  converter 

“  ‘  I  shall  first  give  the  re-  ult  of  my  analysis  of  the  three  samples 

metal: 


44 


69c 


CHEMISTR  Y 


Carbon  .... 

Cupola. 
Pig  (4) 

.  2  830 

Crude. 
Steel  (-). 

i'8oo 

Steel-Iron. 

(S). 

o’993 

Silicon,  with  a  little  titanium 

.  2-950 

0-266 

0-149 

Sulphur  .... 

.  OII3 

o-oi8 

traces 

Phosphorus 

•  i'455 

0-298 

0292 

/\rsemc  .... 

.  0041 

0-039 

0-024 

Manganese 

.  0-318 

0-090 

o-o88 

Calcium  .... 

.  - 

0-319 

0310 

Sodium  .... 

.  - 

0-144 

traces 

Iron  (by  difference) 

.  92*293 

97-026 

98-144 

IOD’OOO  I  OO'OOD  I OOOOO 

“‘It  will  be  obvious  from  a  comparison  of  these  results  that  the  reaction  with 
the  nitrate  of  soda  has  removed  a  large  proportion  of  the  carbon,  silicon,  and 
phosphorus,  as  well  as  most  of  the  sulphur.  The  quantity  of  phosphorus  (0-298 
per  cent.)  retained  by  the  sample  of  crude  steel  from  the  converter  which  I 
analysed,  is  obviously  not  such  as  to  injure  the  quality.* 

“  ‘  The  bar-iron  was  in  our  presence  subjected  to  many  severe  tests.  It  was 
bent  and  hammered  sharply  round  without  cracking.  It  was  forged  and 
subjected  to  a  similar  trial,  both  at  a  dull  red  and  a  cherry  red  heat,  without 
cracking;  it  also  welded  satisfactorily. 

“  ‘  The  removal  of  the  silicon  is  also  a  marked  result  of  the  action  ot  the 
nitrate. 

“‘It  is  obvious  that  the  practical  point  to  be  attended  to  is  to  procure  results 
which  shall  be  uniform ,  so  as  to  give  steel  of  uniform  quality  when  pig  of 
similar  composition  is  subjected  to  the  process.  The  experiments  of  Mr. 
Kirkaldy  on  the  tensile  strength  of  various  specimens  afford  strong  evidence 
that  such  uniformity  is  attainable. 

“‘  I  have  not  thought  it  necessary  to  make  a  complete  analysis  of  the  slag, 
but  have  determined  the  quantity  of  sand,  silica,  phosphoric  and  sulphuric 
acid,  as  well  as  the  amount  of  iron,  which  it  contains.  It  was  less  soluble  in 
water  than  I  had  been  led  to  expect,  and  it  has  not  deliquesced  though  left 
in  a  paper  parcel. 

“  ‘  I  found  that  of  100  parts  of  the  finely-powdered  slag,  1 1  -9  were  soluble  in 
water.  The  following  was  the  result  of  my  analysis: 


Sand . -  47  3 

Silica,  in  combination  .....  6t 

Phosphoric  acid  ......  6"8 

Sulphuric  acid .  ......  ri 

Iron  (a  good  deal  of  it  as  metal)  .  .  .  I2'6 

Soda  and  lime  +  26*1 


I00"0 

“  ‘  This  result  shows  that  a  large  proportion  of  phosphorus  is  extracted  by 


It  is  important  to  poii.r  out  that  as  no  analysis  of  the  finished  steel  tested  by  Mr.  Kirkaldy  is  given, 
it  is  not  improbable  that  this  small  per  centage  of  phosphorus  might  have  been  still  further  reduced 
before  it  arrived  at  its  final  state  of  manulaciure. 

t  The  use  of  lime  was  exceptional  its  use  is  now  discontinued  ;  but  its  u^e  on  that  occasion  no  doubt 
accounted  for  the  slag  being  less  deliquescent  and  soluble  than  it  is  usually  found  to  be. 


IRON. 


691 


the  oxidizing  influence  of  the  nitrate,  and  that  a  certain  amount  of  the  iron  is 
mechanically  diffused  through  the  slag. 

“  ‘  The  proportion  of  slag  to  the  yield  of  crude  steel-irori  was  not  ascertained 
by  direct  experiment ;  but,  calculating  from  the  materials  employed,  its  maxi¬ 
mum  amount  could  not  have  exceeded  23  per  cent,  of  the  weight  of  the  charge 
of  molten  metal.  Consequently,  the  12  6  per  cent,  of  iron  in  ti  e  slag  would 
not  be  more  than  3  per  cent,  of  the  iron  operated  on. 

“‘In  conclusion,  I  have  no  hesitation  in  stating  that  Heaton’s  process  is 
based  upon  correct  chemical  principles :  the  mode  of  attaining  the  result  is 
both  simple  and  rapid.  The  nitric  acid  of  the  nitrate  in  this  operation  imparts 
oxygen  to  the  impurities  always  present  in  cast  iron,  converting  them  into 
compounds  which  combine  with  the  sodium ;  and  these  are  removed  with  the 
sodium  in  the  slag.  This  action  of  the  sodium  is  one  of  the  peculiar  features 
of  the  process,  and  gives  it  an  advantage  over  the  oxidizing  methods  in  common 
use.’ 

“The  slag  produced  is  already  utilized  at  the  works,  and  forms  the  subject 
of  a  new  and  valuable  patent.  There  is  every  reason  to  believe  that  the  pro¬ 
ducts  of  combustion  may,  by  the  means  of  a  mechanical  arrangement  devised 
by  Mr.  Heaton,  be  further  utilized,  and  afford  a  large  set-off  on  the  original 
cost  of  the  nitrate.  It  is  also  a  great  question  whether  the  phosphorus  may 
not  be  most  profitably  reduced  from  the  slag  for  commercial  purposes.” 

Physical  Properties  of  Iron. 

Pure  iron  has  a  bright  white  colour;  though  soft,  it  possesses  great  tenacity 
and  toughness,  and  has  a  specific  gravity  of  7'^44-  It  crystallizes  in  cubes, 
and,  when  made  sufficiently  hot,  possesses  the  valuable  property  of  cohering 
to  another  piece  of  iron,  or  what  is  termed  “welding,”  when  two  clean  hot 
surfaces  are  hammered  together.  Iron  possesses  in  the  highest  degree  the 
valuable  properties  of  malleability,  ductility,  and  tenacity,  and  has  a  curious 
susceptibility  to  magnetism. 

Chemical  Properties. 

Iron  takes  fire  and  burns  in  air,  or  still  better  in  oxygen,  and  if  obtained 
in  the  state  of  powder  by  reducing  ferric  oxide  (Fca03)  at  a  low  red  heat  by 
hydrogen,  it  takes  fire  spontaneously  when  shaken  into  the  air. 

There  are  four  definite  oxides  of  iron,  viz. — 

Ferrous  oxide  or  protoxide  ......  eO 

Ferric  oxide  or  sesquioxide  . . 

The  black  oxide  or  magnetic  oxide  .  .  • 

Ferric  acid,  not  isolated,  and  known  only  in  combination  Hare04 

Amongst  the  chief  salts  of  iron  may  be  noticed  ferrous  sulphide  (f  eS).  and 
ferric  disulphide,  the  “iron  pyrites’  of  nature  (FeS.>) ;  also  the  chlonces, 
iodides,  and  bromides  of  iron;  ferrous  carbonate  and  the  silicates  of  iron ; 
potassic  feri  o-evanide  or  yellow  prussiateof  potash,  and  potassic  ferri-cjamce 
or  red  prussiate,  yielding,  with  a  neutral  or  acid  solution  of  a  ferrous  salt, 
“  Prussian  blue”  (Fe32FeCy6,  a'tfaO) 


> 


■14 - 2 


692 


CHEMISTRY. 


MANGANESE. 

Symbol,  Mn,  Atomic  weight,  55. 

A  metal  discovered  by  Gahn  in  1775  in  an  ore  examined  by  Scheele,  and 
called  by  the  latter  manganese ;  but  why  he  gave  it  that  name  is  known  only 

Swedish  etymology. 

The  most  important  source  of  this  metal  is  the  natural  mineral  called  the 
black  oxide  of  manganese  (Mn02),  used  so  largely  for  making  oxygen  gas  and 
chlorine,  and  likewise  employed  to  impart  a  purple  colour  to  glass. 

Manganese  is  a  greyish-white  metal,  having  a  specific  gravity  of  8-oi3,  and, 
although  brittle,  is  hard  enough  to  scratch  steel.  It  decomposes  water  slowly, 
and  can  only  be  preserved  in  the  metallic  state  (like  potassium)  by  immersing 
it  in  Persian  naphtha.  It  is  feebly  magnetic,  and  is  said  to  exhale  a  peculiar 
odour  when  handled.  There  are  various  oxides  of  this  metal: 

Manganous  oxide  or  protoxide  .....  MnO 
Manganic  oxide  or  sesquioxide  .....  Mn203 

Mangano-manganic  oxide  or  red  oxide  .  .  .  Mn304 

Manganese  dioxide  or  black  oxide  ....  Mn02 

Also  two  other  compounds  of  oxygen  and  manganese,  known  only  in  com¬ 
bination  as  salts,  viz. — 

Potassic  manganate  ....  .  .  K2Mn04 

Potassic  permanganate  ......  KMn04 

The  latter  salts  are  now  largely  employed  as  disinfectants,  because  they  have 
the  power  of  oxidizing  organic  matter,  and  for  that  reason  are  used  in  certain 
processes  as  bleaching  agents.  The  salts  of  manganese  are  too  numerous  to 
discuss  here. 

- -♦ - 

COBALT. 

Symbol,  Co.  Atomic  weight,  587. 

This  metal  was  discovered  by  Brandt  in  1733,  and  was  so  named  after  a 
sprite  or  spirit  that  greatly  troubled  the  miners  in  the  German  mines,  and 
called  by  them  kobold.  It  is  a  rare  metal,  readish-white,  and  having  a  specific 
gravity  of  87.  Cobalt  is  extremely  infusible,  and,  like  iron  in  many  respects, 
is  also  very  tenacious  and  magnetic. 

There  are  two  oxides  of  cobalt  : 

Cobaltous  oxide  or  protoxide  .  .  .  CoO 

Cobaltic  oxide  or  sesquioxide  .  .  .  Co203 

The  protox  de  is  a  valuable  article  in  commerce,  because  it  is  used  to  im¬ 
part  the  blue  colour  to  porcelain  and  pottery,  and  when  combined  with  glass 
is  called  smalt,  a  lovely  b'ue  used  largely  by  paper-stainers.  Cobalt  is  easily 
recognized  by  the  blue  colour  it  imparts  to  borax  in  the  oxidating  flame  of  the 
blowpipe. 

The  important  salts  are  the  sulphide,  chlcyide,  sulphate,  nitrate,  and  car¬ 
bonate  of  cobalt. 

- ♦ - 


NICKEL—  CJIR  OMLUM —  URANI  UAL 


693 


NICKEL. 

Symbol,  Ni.  Atomic  weight,  587. 

The  so-called  “  false  copper,”  or  “ kupfer  nickel ”  of  the  German  miners,  has 
given  the  name  to  this  metal,  discovered  by  Cronstedt  in  1751.  This  minera. 
is  an  arsenide  of  nickel  (NiAs),  and  contains  44  parts  of  nickel  and  56  of 
arsenic.  “Speiss”  is  an  impure  arsenio-sulphide  of  nickel.  Nickel  is  largely 
made  and  used  in  Birmingham  in  the  manufacture  of  “  German  silver,”  an 
alloy  of  1 8-4  nickel,  30-6  zinc,  and  5 1  copper.  Nickel  is  a  white  metal,  having  a 
specific  gravity  of  8-82.  Although  hard,  it  is  both  malleable  and  ductile,  and, 
like  the  other  metals  belonging  to  this  class,  is  feebly  magnetic,  losing  that 
power  entirely  at  626°  F. 

There  are  two  oxides  of  nickel, — the  protoxide  (NiO)  and  the  sesquioxide 
(Nia03).  The  chief  compounds  of  this  metal  are  the  sulphide  of  nickel,  also 
nickel  chloride,  sulphate,  and  carbonate. 

The  salts  of  nickel  impart  a  reddish-yellow  colour  to  borax  fused  in  the 
oxidating  flame  of  the  blowpipe. 


CHROMIUM. 

Symbol,  Cr.  Atomic  weight,  52-5. 

The  name  of  this  metal  — taken  from  the  Greek  xpui/xa,  colour — is  very 
suggestive  of  its  important  use  in  the  preparation  of  certain  pigments  and 
in  calico  printing.  This  metal  was  discovered  by  Vauquehn  in  plumbic 
chromate  in  1797.  The  most  important  ore  containing  it  is  the  chrome  iron¬ 
stone  (FeO,  CraOs),  found  chiefly  in  Sweden  and  North  America.  Chromium 
is  very  infusible,  perhaps  the  most  so  of  all  the  metals,  and  it  has  a  specific 
gravity  of  6  81. 

There  are  four  compounds  of  chromium  and  oxygen,  01  which  the  sesqui- 
oxide  is  the  most  valuable,  whilst  the  chromates  are  largely  used  in  the  manu¬ 
facture  of  pigments,  & c. 

Chromous  oxide  or  protoxide  of  chromium  .  .  CrO 

Chromic  sesquioxide  . . Cr,03 

Chromo-chromic  oxide  ......  CrO,  Cr203 

Chromic  trioxide  or  chromic  acid  .  .  .  Cr03 

The  chief  salts  are  the  chromates,  chromic  chloride,  sulphate,  and  nitrate. 


URANIUM. 

Symbol,  U.  Atomic  weight,  120. 

In  the  same  year  that  Klaproth  discovered  this  metal — viz.,  in  1789  Her- 
schel  had  discovered  the  planet  which  now  bears  the  same  name,  and  in  honour 
of  the  discoverer  of  the  new  planet  the  distinguished  chemist  gave  it  the  name 
of  uranium.  The  mineral  called  pitchblende  contains  nearly  80  per  cent,  ot 
the  black  uranium  oxide  (2UO.  U-O3) ;  it  also  constitutes  a  part  of  the  two 
minerals  termed  chalcolite  and  uranite  or  hydrated  calcic  diuranic  phosphate. 

Uranium  is  described  as  a  steel-white  metal,  analogous  in  its  chemical  re- 


694 


CHEMISTR  V 


lations  to  iron  and  manganese.  There  are  two  well-marked  oxides,  uranous 
oxide  or  protoxide  (UO),  and  uranic  oxide  or  sesquioxide  (U2Os). 

The  salts  of  uranium  are  green,  such  as  the  chlorides  U2C13  and  UC1. 

The  chief  use  of  this  metal  is  in  glass  staining,  the  uranous  oxide  imparting 
a  perfect  black,  and  the  uranic  oxide  a  yellow,  which  shines  most  curiously  in 
light  containing  Stokes’s  rays,  or  in  those  that  exist  beyond  the  extreme  violet. 

- -♦ - 

INDIUM. 

Symbol,  In.  Atomic  weight,  74. 

Discovered  by  Reich  and  Richter  in  zinc  blende,  from  the  peculiar  lines 
obtained  by  heating  this  substance  in  the  Bunsen  flame,  and  then  viewing  it 
with  the  spectroscope.  Two  bright  lines  were  seen  in  the  blue  and  indigo  rays 
of  the  spectrum,  not  coincident  with  any  other  known  element.  It  is  stated 
to  be  a  white  malleable  metal,  having  a  specific  gravity  of  about  7‘36,  and  is 
easily  fusible. 

Indie  oxide  is  white.  A  yellow  sulphide  and  a  white  chloride  or  acetate  of 
indium  have  already  been  obtained  and  experimented  with. 


CLASS  VI. 

TIN,  TITANIUM,  NIOBIUM,  TANTALUM. 
The  Tin  Class. 


TIN. 

Symbol,  Sn  (Stannum).  Atomic  weight,  118. 

This  metal  appears  to  have  been  known  from  the  earliest  periods,  and  is 
even  mentioned  in  the  books  of  Moses.  Fig.  516  will  remind  the  reader  that 
it  is  chiefly  obtained  from  Cornwall  and  Devonshire,  from  the  ore  called  tin¬ 
stone,  stannic  oxide  or  binoxide  of  tin  (Sn02).  Tin  is  a  yellowish-white  metal, 
having  a  specific  gravity  of  7'292 :  it  is  malleable,  and  is  sold  in  sheets  called 
“tin  foil,”  used  largely  with  mercury  in  the  silvering  of  looking-glasses. 

The  alloys  of  tin  are  very  important.  Tinned  iron  or  tin  plate,  Britannia 
metal,  solder,  speculum,  bell  and  gun  metal,  and  bronze  are  all  illustrative  of 
its  importance  in  the  metallurgical  arts. 

There  are  two  principal  oxides  of  tin,  viz.,  stannous  oxide  or  protoxide  of 
tin  (SnO),  stannic  oxide  or  binoxide  of  tin  (Sn02).  Stannic  sulphide  or  mosaic 
gold,  and  the  chlorides  of  tin  are  valuable  compounds  used  in  decorating,  and 
as  "  mordant  by  the  dyer  and  calico  printer. 

- ♦ - 

TITANIUM  (symbol,  Ti,  atomic  weight,  50), 

NIOBIUM,  and 
TANTALUM 

are  very  rare  metals,  which  need  not  be  described  here. 


MOL  YBDENUM— ARSENIC. 


695 


Fig.  5 1 6.  — A  Tin-Mine  in  Cornwall. 


CLASS  VII. 

MOLYBDENUM,  VANADIUM,  TUNGSTEN. 

The  Tungsten  Class. 

TUNGSTEN. 

Symbol,  W  (Wolfram).  Atomic  weight,  184. 

The  only  metal  of  this  class  that  specially  deserves  attention  (the  other 
two  being  extremely  rare)  is  tungsten.  It  is  a  greyish-black  powder,  which 
becomes  brilliant  if  burnished,  and  has  a  specific  gravity  of  i/'6. 

There  are  two  oxides,  the  dioxide  (WO*)  and  tungsten  trioxide  (V  Os). 

Tungsten  is  sometimes  employed  in  the  manufacture  of  steel,  to  which  it  is 
said  to  impart  a  peculiar  toughness. 


- — + — — — 

CLASS  VIII. 

ARSENIC,  ANTIMONY,  BISMUTH. 

These  metals  have  already  been  described  (see  pages  609 — 616). 


696 


CHEMIST. R  Y. 


CLASS  IX. 

LEAD,  THALLIUM. 
The  Lead  Class. 


LEAD. 

Symbol,  Pb  (Plumbum).  Atomic  weight,  207. 

Lead  ore  is  very  abundant  in  various  parts  of  England  :  the  chief  ore  is  the 
native  plumbic  sulphide,  protosulphide  of  lead,  or  galena  (PbS).  Lead  is  a 
bluish-white  metal,  having  a  specific  gravity  of  11 '36:  it  marks  paper,  and  is 
so  soft  that  it  is  easily  indented  with  the  nail.  It  is  malleable,  ductile,  and 
sufficiently  tenacious  for  the  purposes  to  which  it  is  applied.  It  is  easily 
melted,  and  fuses  at  a  temperature  of  620°  F.,  and  is  most  extensively  used 
for  making  leaden  pipes,  cisterns,  and  for  the  gutter-work  and  covering  of 
houses.  Type,  pewter,  Britannia  and  Queen’s  metals,  all  contain  lead.  The 
red  oxide  is  used  in  glass-making,  and  the  carbonate  and  chromates,  with  the 
oxychlorides  of  lead,  are  largely  employed  as  pigments. 

Lead  is  the  usual  messenger  of  death  in  modern  battles,  and  receives  one 
of  its  most  destructive  forms  in  the  Sneider  bullet,  which,  with  its  cartridge 
and  sell-exploding  arrangement  attached,  is  shown  at  Fig.  517. 


Fig.  517. —  The  Sneider  Cartridge. 


The  terrible  slaughter  of  the  army  of  King  Theodorus  in  the  battle  that 
preceded  the  fall  of  Magdala  was  due  to  the  mistake  the  King  made  in  exciting 
nis  troops  to  attack  what  he  thought  u’ere  baggage-mules,  but  which  were,  in 
fact,  steel  guns  and  rocket  batteries.  His  men,  crowded  together,  were  shot 
down  by  hundreds.  From  the  Sneider  bullets  and  shells  the  Abyssinians 
received  the  most  frightful  w'ounds,  and  some  w'ere  discovered  after  the  battle 
with  half  their  skulls  blowm  off. 

There  are  four  oxides  of  lead  :  a  black  suboxide  (Pb20),  plumbic  oxide  or 
protoxide  of  lead  (PbO),  plumbic  dioxide  or  peroxide  of  lead  (Pb02),  minium 
or  red  lead  (PbO,  PbOa).  The  sulphide,  chloride,  oxychloride,  and  the  car¬ 
bonates  of  lead  represent  the  most  valuable  salts  of  this  metal. 

—  -» — — 

THALLIUM. 

Symbol,  Tl.  Atomic  weight,  204. 

This  metal  was  discovered  by  Mr.  Crookes,  the  editor  of  the  “  Chemical 
News,”  who  describes  his  discovery  as  strictly  analogous  to  that  of  selenium 


THALLIUM, ; 


697 


Fig.  c  j  S. — The  use  of  the  Sneider  Rifle  in  the  Battle  that  preceded  the 

fall  of  Magdala. 


After  a  picture  by  Mr.  Baines. 


by  Berzelius.  The  observation  of  a,  brilliant  green to*  hr  *£££“?»£ 
SLSF  aSfcU-i  (i  Peen  tinge),  on  account  of  the 

mi st: 

to  Mr.  Crookes's  lecture  “On  the  D'sc°v„7»riLI  na^Ss «  itten  by  the  dis- 
vered  at  the  Royal  Institution,  also  to  the  various  papers  y 

coverer  in  the  “Chemical  News.” _ _ 

..  *  ,0/ .  \  lecture  by  William  Crookes* 

*  Royal  MtK'1^'’’  Paraon,  Printer,  Paternoster  How. 


698 


CHEMISTRY. 


CLASS  X. 

COPPER,  MERCURY,  AND  SILVER. 
The  Silver  Class. 


SILVER. 

Symbol,  Ag  (Argentum).  Atomic  weight,  108. 

Silver  is  another  of  the  metals  well  known  and  appreciated  by  the  ancients. 
It  is  sometimes  met  with  in  the  native  state,  but  is  more  generally  associated 
with  lead  as  argentic  sulphide.  By  Pattinson’s  admirable  process  the  pure  lead 
is  crystallized  out  of  the  alloy  of  lead  and  silver  obtained  by  smelting  lead 
ores  containing  a  certain  quantity  of  silver,  and  then,  by  “  cupellat'ion,”  the 
silver  is  obtained  pure. 

Any  specimen  of  lead  or  galena  supposed  to  contain  silver  is  first  pow¬ 
dered,  weighed,  and  then  well  mixed  with  twice  its  weight  of  sodic  carbonate, 


Fig.  519. — Agate  Pestle 
and  Mortar. 


Fig.  521. — Muffles. 


and  8  per  cent,  of  powdered  charcoal.  This  mixture  is  placed  into  a  crucible 
sufficiently  large,  and  gradually  heated  till  the  boiling  up  of  the  materials 
ceases,  when  the  heat  is  urged  quickly  to  a  bright  redness,  and  the  crucible  is 
then  removed  and  allowed  to  cool.  The  button  of  lead  is  now  placed  on  a 
“  cupel,”  made  with  damp  bone-ash  compressed  into  a  proper  mould  (Fig.  520). 
When  the  cupel  is  made  it  is  easily  pushed  out  of  the  mould  and  dried.  The 
cupel  is  now  placed  in  a  muffle  (Fig.  521),  which  is  made  of  the  same  ma¬ 
terial  as  the  best  crucibles.  The  muffle  is,  of  course,  previously  heated  in  a 
proper  furnace,  of  which  most  useful  examples  are  given  in  the  cut  Fig.  522. 

By  the  proper  management  of  the  heat,  the  lead  is  oxidized,  and  sinks  into 
the  pores  of  the  cupel,  and  at  last  a  tiny  bead  of  silver  is  apparent,  which  is 
taken  out  of  the  cupel  when  cold,  and  weighed. 

Silver  is  a  reddish-white  metal,  and  possesses  all  the  best  physical  properties 
of  a  metal,  viz.,  malleability,  ductility,  and  tenacity.  It  has  a  specific  gravity 
of  1  o1 5  3,  and  melts  at  1,873°  F.  When  heated  in  a  small  cup  or  crucible  of 
charcoal  in  the  voltaic  arc,  it  volatilizes,  and  the  hot  vapour  emits  a  light, 
which,  passed  through  prisms,  affords  two  bright  green  lines  (see  frontispiece), 
very  characteristic  of  the  presence  of  this  metal. 

Pure  silver,  instead  of  having,  like  palladium,  potassium,  and  mercury,  the 
property  of  absorbing  hydrogen,  prefers  its  usual  companion,  oxygen,  and  is 
said  to  take  up,  whilst  in  the  liquid  state,  twenty-two  times  its  bulk  of  this 
element.  The  metal  gives  out  the  oxygen  wlv. n  it  assumes  the  solid  state, 


STL  VER. 


F IG.  522. — Furnaces,  for  assaying  Silver  and  Gold. 

a,  furnace  arranged  with  muffles  sand  bath  above,  and  retoit;  b,  furnace,  with  earthen  retort,  and 
tube  for  other  experiments  These  furnaces  are  made  of  s  .eet  iron,  lined  with  fire-clay,  and  are  sold 
by  How,  Foster  Lane,  City. 

There  are  three  oxides  of  silver: 

Argentous  oxide  or  suboxide  of  silver  .  .  Ag.O 

Argentic  oxide  or  protoxide  of  silver  .  .  Ag20 

Argentic  peroxide . 

The  argentic  sulphide  (AgsS)  is  the  mineral  which 
yields  the  largest  proportion  of  silver.  The  chloride 
of  silver  is  an  important  body;  there  is  a  sub-chloride 
(AgaCl),  but  the  symbol  of  the  former,  called  argentic 
chloride,  is  AgCl. 

In  the  assay  of  silver  by  the  wet  process,  the  de¬ 
termination  of  the  real  quantity  of  the  metal  in  any 
given  specimen  is  brought  within  an  error  of  ‘5  in 
1,000,  whilst  cupellation  may  vary,  even  in  the  most 
experienced  hands,  as  much  as  2  in  1,000.  The  solu¬ 
tion  of  the  alloy  is  tested  by  a  measured  quantity  of  a 
standard  solution  of  sodic  chloiide  (common  salt);  Fig.  523. — Precipitat- 
and  this  test,  or  that  of  hydrochloric  acid,  is  so  delicate  ing  Glass  for  Argentic 
that  it  will  detect  one  part  of  silver  in  200,000  parts  Chloride,  with  Funnel 
of  water.  The  chloride  of  silver  settles  to  t lie  bottom  and  Beaker  Glass  for 
of  the  vessel  in  which  it  is  precipitated  and  it  may  be  filtering. 


700 


chemistry. 


Iplllp 

'WE9t 

mmt. 


li;  i:’"/. 


■  ■  "• 


THE  MILTON  SHIELD, 


Fig.  5  2  _l  — E! king  ion 's  Mi/ton  Shield 


702 


CHEMISTR  Y. 


collected,  washed,  dried,  and  weighed,  to  verify  the  standard  solution  of 
salt. 

When  exposed  to  the  light,  it  gradually  blackens,  and  hence  is  used  for 
taking  copies  of  negative  photographs,  the  chloride  which  is  not  acted  on  by 
the  light  being  subsequently  dissolved  out  by  a  solution  of  hyposulphite  of 
sodium.  Zinc  reduces  the  argentic  chloride  to  the  metallic  state. 

Argentic  chloride  is  soluble  in  a  solution  of  potassic  cyanide,  and  is  used 
for  silvering.  A  better  silvering  solution  is  the  argentic  cyanide  obtained  by 
precipitating  a  solution  of  argentic  nitrate  with  one  of  potassic  cyanide,  and 
dissolving  the  argentic  cyanide  in  an  excess  of  the  potassic  cyanide. 

From  either  of  these  solutions  of  silver  the  most  beautiful  works  of  art 
are  formed  by  precipitating  the  silver  in  moulds  by  a  current  of  electricity. 

Fig.  524  fpp.  646,647)  represents  Messrs.  Elkington  and  Co.’s  magnificent 
Milton  Shield. 

This  remarkable  work  of  art  in  repousse  silver  has  since  been  purchased  by 
he  Government  for  the  South  Kensington  Museum,  and  cost  the  firm  nearly 
,£3,000  to  make.  It  received  two  gold  medals  at  the  Great  French  Exhibi¬ 
tion,  viz.,  one  for  the  firm  and  one  for  the  artist.  The  great  firm  of  Elkington 
has  now  been  established  in  Birmingham  and  London  for  many  years,  and 
has  produced  more  than  any  other  house  those  beautiful  designs  in  silver 
which  have  raised  the  character  of  English  silversmith’s  work  to  the  highest 
pitch  of  eminence.  Amongst  the  important  works  of  art  made  by  Messrs. 
Elkington  since  the  Exhibition  of  1862  are  the  following,  all  of  which  have 
received  the  highest  encomiums  from  those  capable  of  judging  of  art-work, 
to  say  nothing  of  the  numerous  medals  awarded: 

1867,  Paris  Exhibition:  The  Elcho  Challenge  Shield;  the  International 
Challenge  Trophy;  the  Milton  Shield  (since  purchased  by  the  Government 
for  the  Kensington  Museum);  enamelled  and  silver-gilt  baptismal  gift  from 
Her  Majesty  the  Queen  to  the  son  of  H.R.H.  the  Prince  of  Wales;  bronze 
statue,  10  ft.  6  in.  high,  of  H.R.H.  the  late  Prince  Consort,  by  W.  Theed,  Esq., 
erected  at  Balmoral;  the  bronze  8  ft.  statues  of  OliverGoldsmith  and  Edmund 
Burke,  both  by  J.  H.  Foley,  R.A.,  for  the  University  of  Dublin;  and  they  are 
now  proceeding  with  the  four  bronze  statues,  7  ft.  6  in.  high,  each  intended  for 
the  Plolborn  Viaduct. 

There  are  other  useful  salts  of  silver,  viz.,  argentic  bromide  (AgBr),  argentic 
iodide  (Agl),  argentic  fluoride  (AgF),  the  argentic  sulphate  (Ag.;SO,),  and 
especially  argentic  nitrate  (AgN03).  The  argentic  phosphates  are  also  worthy 
of  notice. 

- ♦ - 

COPPER. 

Symbol,  Cu  (Cuprum).  Atomic  weight,  63*5. 

Some  years  ago  Professor  Tennant,  of  the  Strand,  the  celebrated  mineral¬ 
ogist,  deposited  a  great  mass  of  very  hard  native  copper  from  North  America 
at  the  Polytechnic.  In  England  the  mines  of  Cornwall  supply  the  clean  copper 
ore  which  is  smelted  at  Swansea.  The  process  of  roasting,  melting  and  granu¬ 
lating,  and  gradually  refining  the  metal,  is  very  elaborate. 

Copper  is  extremely  malleable  and  ductile,  and  has  a  specific  gravity  of 
8’92i  to  8'952 ;  it  has  a  red  colour,  and  emits  a  peculiar  odour  when  handled. 
It  is  used  in  many  different  ways  for  coinage  and  the  sheathing  of  ships,  and 
is  an  important  constituent  of  brass  and  other  valuable  alloys. 


COPPER. 


703 


At  the  Great  Exhibitions  in  this  country  and  Paris,  the  copper  trophies  were 
always  conspicuous  objects;  and  the  French  especially  now  compete  very 
closety  wph  the  English  in  the  manufacture  of  those  large  copper  vessels 
called  vacuum  pans,”  used  in  sugar-boiling,  of  which  the  following,  taken 
from  L  re  s  Dictionary,  is  a  good  illustration. 


Fig.  525. 

A,  represents  the  vacuum  spheroid  ;  b,  the  n-ck,  with  the  lid.  From  the  side,  b,  a  pipe  passes  into  the 
lower  extremity  of  the  bent  pipe,  Fj  u,  terminates  in  the  pipe:  is,  valve  connec  ed  with  the  vacuum 
main  pipe,  k;  f,  me  .sure  cistern;  h,  valve  for  cutting  ort  supply;  1,  stop-cock;  c,  barometer;  m, 
proof-stick  ;  n,  cistern  pipe  for  excess  syrup. 

Copper  does  not  oxidize  in  pure,  dry,  or  moist  air,  and  hence  is  used 
extensively  in  Moscow  for  covering  the  domes  of  churches.  1  here  are  two 
oxides  of  copper,  viz.,  cuprous  oxide  (Cu30),  and  cupric  oxide  (CuO).  1  lie 
chief  salts  of  this  metal  are  cupric  sulphate  (CuSOt.  5 11,0),  cupric  nitrate 
(Cu4N03,6Hs0),  cupric  sulphide  (CuS),  cupric  carbonate,  and  hydrated  dibasic 
carbonate  or  malachite  (CuO,  HaO,  CuC03),  so  plentiful  in  the  Russian  do¬ 
minions.  The  art  of  electrotyping  is  also  carried  out  by  Messrs.  Ellcinyjton 
with  the  greatest  success,  and  the  finest  works  in  copper  are  executed  by  that 
house,  the  metal  being  deposited  from  the  cupric  sulphate  by  electricity. 


7°4 


CHEMISTR  V. 


MERCURY. 

Symbol,  Hg  (Hydrargyrum).  Atomic  weight,  200. 

The  title  hydrargyrum  conferred  on  mercury,  is  derived  from  the  Greek 
vSw p  (liquid),  and  d'pyvpov  (silver)  or  quicksilver.  It  is  sometimes  found 
native,  but  is  usually  prepared  from  cinnabar,  a  mineral  sulphide  of  mercury. 

Mercury  is  a  very  brilliant  metal,  fluid  at  all  ordinary  temperatures,  and 
having  a  specific  gravity  of  I3'56.  At  all  temperatures  above  410  F.  it  vola¬ 
tilizes  slightly ;  hence  the  danger  to  workmen  using  this  metal  either  for  silver¬ 
ing  looking-glasses,  or  thermometer  and  barometer  making. 

Mercury  freezes  at  — 37°9'  F.,  and  is  not  tarnished  by  exposure  to  damp  or 
dry  air  at  ordinary  temperatures. 

There  are  two  principal  oxides,  mercurous  oxide  or  suboxide  of  mercury 
(Hgj>0),  and  mercuric  oxide  or  red  oxide  of  mercury  (HgO).  The  most 
valuable  salts  of  mercury  are  the  native  sulphides,  the  chlorides  of  mercury, 
mercurous  chloride  or  calomel  (HgCl),  and  mercuiic  chloride  or  corrosive 
sublimate  (HgCl2).  The  mercuric  iodide,  mercuric  sulphate,  and  mercuric 
nitrate  are  some  of  a  long  list  of  mercurial  salts  presenting  many  interesting 
features. 


- ♦- - 

CLASS  XI. 

GOLD,  PLATINUM,  PALLADIUM,  RHODIUM,  RUTHENIUM, 

IRIDIUM,  OSMIUM. 

The  Gold  Class. 


PLATINUM. 

Symbol,  Pt.  Atomic  weight,  I97‘l. 

It  was  the  sagacity,  the  patience,  and  learning  of  the  late  Dr.  WollastoP 
that  overcame  all  the  difficulties  connected  with  the  manipulation  of  the  oiv 
of  platinum,  and  not  only  demonstrated  how  that  metal  was  to  be  extracted 
from  the  mineral,  but  also  invented  a  method  by  which  the  metal,  originally  in 
the  form  of  powder,  was  gradually  brought  to  the  solid  state,  and  rendered 
both  malleable  and  ductile. 

The  name  of  the  metal  is  derived  from  platina  (little  silver),  and  it  was  first 
obtained  by  Wood  in  1741. 

Platinum  comes  chiefly  from  the  Ural  Mountains,  although  some  is  obtained 
in  Mexico  and  Brazil,  likewise  in  California  and  Australia.  It  is  tolerably  hard, 
and  has  a  specific  gravity  of  21*5.  The  colour  of  this  metal  is  white,  and  when 
polished  it  exhibits  considerable  brilliancy.  The  ductility  and  tenacity  of 
platinum  have  been  compared  to  that  of  iron. 

It  is  quite  infusible  by  any  ordinary  furnace  heat,  but  melts  in  the  voltaic 
arc  of  a  powerful  battery;  and  when  enclosed  in  a  hollow  made  in  a  lump  of 
pure  lime,  may  be  fused,  according  to  the  process  of  Deville  and  Debray,  by 
the  oxyhydrogen  blowpipe. 

Platinum  is  largely  used  for  crucibles,  tubes,  evaporating-vessels  required 


GOLD. 


7°5 


for  laboratory  purposes.  Platinum  foil  for  batteries  and  analytical  experi¬ 
ments  on  the  small  scale,  and  platinum  wire,  are  indispensable.  Large  stills, 
usually  gilt  inside,  are  used  for  the  concentration  of  oil  of  vitriol :  the  gilding 
of  the  still  prevents  the  acid  finding  its  way  through  the  pores  of  the  metal. 

There  are  two  oxides  of  platinum,  the  protoxide  or  platinous  oxide  (PtO)  and 
platinic  oxide,  the  dioxide  (Pt02) ;  also  two  sulphides,  PtS  and  PtS2. 

One  of  the  most  important  salts  of  the  chlorides  is  the  platinic  chloride, 
always  spoken  of  in  the  old  standard  works  as  the  bichloride,  but  now  called 
the  tetrachloride  (PtC4).  By  gently  heating  this  salt,  finely-divided  metallic 
platinum  or  platinum  black  is  obtained ;  or  a  solution  of  platinic  chloride  may 
be  precipitated  with  ammonium  chloride:  the  amnionic  platinum  chloride  is 
collected,  washed,  dried,  and  heated  red  hot,  and  then  forms  a  finely-divided 
porous  mass  called  “spongy  platinum,”  which  becomes  red  hot  immediately 
a  jet  of  cold  hydrogen  gas  is  directed  upon  it,  because  its  pores  are  always 
full  of  oxygen,  and  the  two  gases,  by  the  intervention  of  the  spongy  platinum, 
unite  and  form  water.  This  power  of  condensing  gases  upon  its  surface  is  a 
very  curious  property  of  finely-divided  clean  platinum.  Platinum  chloride  is 
always  used  to  determine  quantitatively  potassium  or  ammonium  in  analytical 
researches. 

Palladium  and  Rhodium  were  discovered  by  Wollaston  in  the  ore  of 
platinum  in  the  year  1803;  IRIDIUM  and  Osmium  by  Tennant  in  the  same 
year;  Ruthenium  by  Claus  in  1845.  All  these  metals  were  discovered  in  the 
ore  of  platinum,  and  might  have  been  known  much  earlier  if  the  spectroscope 
had  been  in  use  in  the  time  of  Wollaston.  The  last  metal,  but  certainly  not  the 
least  in  importance,  is  gold. 

- ♦ - 

GOLD. 

Symbol,  Au  (Aurum).  Atomic  weight,  i()6‘6. 

California  and  Australia  are  now  only  spoken  of  as  modern  Ophirs  and  the 
lands  of  gold.  Peru,  Brazil,  Hungary,  the  Ural  Mountains,  and  even  Africa, 
hide  their  diminished  heads  before  the  first-named  countries,  although  it  was 
from  these  countries  that  gold  was  chiefly  obtained  up  to  within  the  last 
twenty-five  years. 

Gold  is  found  in  the  native  state  in  various  forms,  sometimes  crystallized  in 
octohedral  cubes,  or  tetrahedra  occasionally  in  thin  plates,  stringy  and  arbor¬ 
escent,  and  in  irregular  lumps  called  “nuggets;”  indeed,  the  latter  title  has 
become  a  household  word,  and  the  expression  “he  has  found  a  nugget  amounts 
to  an  announcement  of  sudden  good  fortune. 

The  colour  of  gold  (a  full,  rich  yellow)  is  known  to  all.  1  he  specific  gravity 
of  this  precious  metal  is  I9'34*  Gold  is  too  soft  to  be  used  alone,  and  is, 
therefore,  usually  alloyed  with  copper.  It  takes  very  high  rank  in  the  pro¬ 
perties  of  malleability,  ductility,  and  tenacity.  Gold  melts  at  a  temperature 
of  2,01 6°  F.,  and  any  day,  at  the  Polytechnic,  may  be  seen  the  conversion  ot 
gold  wire  into  a  purple  smoke  by  the  discharge  of  the  Leyden  battery,  show¬ 
ing  the  remarkable  division  of  particles  of  which  this  and  other  metals  are 
capable. 

The  true  solvent  of  gold  is  nitro-muriatic  acid  (a-ntn  reg.n) ;  and  after 
evaporating  the  solution,  the  auric  chloride  is  obtained;  this,  re-dissolvcd  in 
plenty  of  water  and  filtered  to  get  rid  of  any  argentic  chloride,  is  precipitated 

45 


706 


CHEMISTR  Y 


with  a  solution  of  ferrous  sulphate.  The  gold  gradually  settles  to  the  bottom 
of  the  vessel,  and  looks  like  brown  mud  by  reflected,  but  purple  by  trans¬ 
mitted,  light.  The  liquid  may  be  poured  off,  and  more  water  added ;  the  finely- 
divided  gold  is  then  boiled  two  or  three  times  with  hydrochloric  acid,  and 
finally,  being  washed  and  dried,  may  be  melted  in  a  crucible  under  borax,  or, 
better  still,  hydropotassic  sulphate. 

Gold  is  used  for  various  ornamental  purposes,  either  spread  over  other  sub¬ 
stances,  as  in  the  art  of  gilding,  or  employed  to  impart  a  magnificent  ruby  red 
to  glass.  Perhaps  one  of  the  best  illustrations  of  the  ingenious  use  of  this 
metal  is  in  the  fabrication  of  ornaments  for  the  person. 


Fig.  526 .—Specimens  of  Streeter’s  Machine-made  Jewellery  of  1  S-carat  Gold. 


In  a  little  work  entitled  “  Hints  to  Purchasers  of  Jewellery,”  Mr.  Streeter 
has  done  good  service  to  the  public  by  stating  plainly  the  relative  value  of  the 
different  qualities  of  gold,  and  it  is  from  this  work  the  following  quotations 
are  taken. 

How  Jewellery  is  made  by  Machinery. 

Mr.  Streeter  says,  “I  now  proceed  to  describe  the  manufacture  of  golden 
ornaments;  and  that  this  may  be  the  more  readily  understood,  I  propose  to 
trace  the  construction  of  a  bracelet.  Suppose  a  skilled  workman  be  required 
to  fashion  one  by  hand,  the  process  would  be  this :  the  necessary  quantity 
of  gold  having  been  weighed  out — the  gold  would  probably  be  in  a  piece  of 
about  a  quarter  of  an  inch  in  thickness — it  would  first  be  hammered  to  the 
required  tenuity;  then,  having  cut  it  into  strips,  the  artificer  would  construct 
the  flat  portion  of  the  bracelet  which  goes  round  the  wrist,  and  make  the 


GOLD. 


707 


chenille  or  raised  edge  ;  then  he  would  model  the  centre  ornament  by  means 
of  the  hammer  and  chisel,  and  cut  out  the  beads  and  fasten  them  on  ;  lastly, 
he  would  solder  the  various  parts  together,  and  add  the  joint  and  snap. 

“  The  construction  would  of  course  in  this  way  occupy  much  time,  and  as  it 
could  only  be  accomplished  by  a  skilful  workman,  the  bracelet  must  neces¬ 
sarily  cost  a  high  price. 

“  But  now  let  us  see  what  machinery  can  do  to  lessen  both  labour  and  price. 
In  the  first  place,  the  gold,  instead  of  being  hammered  into  the  required  thick¬ 
ness,  is  passed  through  the  steam  rolling  machine  (a,  Fig.  527),  and  can  be 
pressed  out  to  any  extent  in  a  few  minutes.  It  is  then  with  the  greatest 


Fig.  527. 

a  a  a,  rollers;  b,  steam  engine;  c,  bellows;  d,  tap  to  regulate  Mipp'y  of  air  to  furnace;  r,  furnace;  /, 
cutting  machine ;  g,  plate  of  ro  led  gold ;  h,  thin  slips  of  gold  cut  from  plate ;  t,  c  ike  of  gold  ;  j,  tl  c 

same  foiled. 

rapidity  cut  into  strips  by  the  cutting  press  (f,  Fig.  527).  A  die  (Fig.  528) 
having  been  prepared  (and  every  one  who  has  a  monogram  tor  his  note-paper 
knows  how  quickly  and  inexpensively  dies  are  made),  a  strip  of  the  gold  is 
put  into  the  “  monkey  press,”  an  apparatus  of  considerable  power,  and  with 
two  separate  blows  the  two  halves  of  the  bracelet  are  stamped  out.  Mean¬ 
while,  by  means  of  another  die  and  press  oj  less  power ,  the  centre  ornament 
is  with  equal  facility  formed ;  and  all  that  remains  for  the  workman  to  do  by 
hand  is  to  joint  the  bracelet  and  put  on  the  snap,  and  to  polish  it. 

“In  the  ornamentation  of  jewellery  gold  wire  of  different  degrees  of  fine¬ 
ness  is  used.  This  wire  is  made  as  follows:  the  gold  is  first  cut  into  strips  by 
means  of  the  cutting  press.  Each  strip  is  then  forcibly  drawn  through  an 
aperture  in  a  steel  plate,  which  rounds  it  and  forms  it  into  wire.  I  lus  is  again 
passed  through  apertures,  smaller  and  smaller,  until  the  required  size  is  ob¬ 
tained.  These  plates  are  called  “  gauges,”  and  are  capable  of  attenuating  wire 
to  any  extent.  If  requires  considerable  power  to  force  the  strips  througli  the 

46—2 


708 


CHEMISTRY. 


Fig.  528.  Fig.  530. —  The  Lapping  Machine,  used  for 

polishing  the  bright  parts  of  Gold  Ornaments. 


gauges,  and  this  power  is  obtained  by  means  of  the  “  drawbench.”  This 
description  refers,  of  course,  to  plain  wire  only;  ornamental  wires  have  to 
undergo  an  additional  process. 

“A  bracelet  would  take  a  skilled  workman  «>days  to  make  by  hand,  whilst, 
with  the  aid  of  the  machinery  1  have  described,  the  same  ornament,  including 
the  necessary  hand-work,  such  as  jointing,  polishing,  &c.,  can  be  made  in  two 
days. 

“  From  the  above  brief  description  it  will  be  readily  understood  how  it  is 
that  really  good  jewellery  may  be  obtained  at  a  comparatively  small  cost,  and 
yet  a  good  profit  may  be  had  by  the  vendor.  The  price  of  the  gold  contained 
in  any  one  ornament  is  the  same,  both  to  the  jeweller  and  to  the  purchaser ; 
the  profit  to  the  former  is — or  ought  to  be— derived  from  the  workmanship, 
and  the  more  quickly  he  Can  manufacture  such  articles,  the  cheaper  he  can 
sell  them,  getting  for  himself  a  fair  profit,  and  giving  to  the  public  advantages 
which  they  could  not  have  had  under  the  old  system. 

“  Pure  gold  is  represented  by  the  figures  24,  and  is  called  24-carat  gold ;  but 


GOLD, 


709 


it  is  seldom  to  be  procured  in  a  state  of  perfect  purity,  as  it  requires  a  long 
chemical  process  so  to  obtain  it,  which  adds  so  much  to  its  cost  that  it  is  too  ex¬ 
pensive  for  commercial  purposes.  ■  That  which  is  called  24-carat  is  really  only 
23a  or  h  which  is  quite  good  enough  for  all  practical  purposes.  This  being 
purchased  by  the  manufacturing  jeweller,  is  alloyed  according  to  his  taste  or 
conscience;  which  latter,  1  am  afraid,  is  not  always  of  the  most  sensitive 
nature.” 


TABLE  SHOWING  THE  DIFFERENT  QUALITIES  OF  GOLD  MANUFACTURED  IN 
DIFFERENT  PARTS  OF  THE  WORLD. 


England 
France  . 

Denmark 
Baden  . 

Germany  (all  States) 
Russia  . 

Austria  . 

1  taly 
Holland 
Africa  . 

India 
Rome 

United  States 
Norway  and  Sweden 
Belgium 
Spain 

Switzerland 
Geneva  . 

China 
J  apan 
Brazil 
Hamburg 
Turkey  . 

Greece  . 

Persia  . 

Egypt  . 

Rio  Janeiro 
Chili  . 

Peru 
Siam 
Australia 
Mexico 


Carat. 

From  I  worth 
18  „ 

18  „ 

14  „ 

«2  „ 

1 5  „ 

10  „ 

12  „ 

4 
23 
22 

18 
1 

18 
18 
18 
18 

•4 

16 
18 
18 


yy 

» 

yy 

yy 

yy 

yy 

yy 

yy 

yy 

All 

F  rom 
All 

F  rom 
All 

yy 

From 


yy 

All 


yy 

yy 

yy 

yy 

yy 

yy 

yy 


yy 

yy 


From 


yy 

yy 


Imported  from 


I  ^  — 

18 

10 

3 

18 

1 

1 

1 


r> 

r> 


3 

3 

3 

9 

2 

* 

*  a 

>5 

2 

»4 

1 

*7 

3 
3 
3 
3 
3 
3 
9 

16 

3 

3 

1 1 

3 

15 

10 

3 

3 

3 

3 


d. 

6 

Si- 

84 
64 
5  4 

1 

44 

5  4 

2 

6 

io| 

84 


8* 

84 

8* 

84 

74 

84 

84 

34 

84 

4} 

74 

84 

6 

6 

6 


s.  d. 

17  iwa 


Carat.  £ 

to  22  worth  3  17  IO 
Only  common  by  spe¬ 
cial  permission. 


to 


>5 

22 

18 

22 

22 

234 

18 

22 


worth 


13 

>7 

3 

17 

17 


4  3 
3  3 


1  w2 
84 
104 
ioi 


>1 


84 


3  >7  >o4 


Watch-cases  only, 
to  23!  worth  440 
440 


23f 


18 

16 

234 

22 

22 

22 


3  3  8| 


16 
3 

1 7 
>7 
*7 


74 

G 


104 

10.4 

io4 


Nearly  pure,  fine  work.  . 

Same  as  England,  except  that  made  up  from  the  diggings. 
Principal  manufacture  fine. 


Any  quality  is  allowed  to  be  imported  into  these  countries. 

“The  kinds  of  gold  best  adapted  for  manufacturing  purposes  are  18  or  16- 
arat.  Trinkets  made  of  these  qualities  not  only  keep  their  shape  and  bald¬ 


ness,  and  allow  of  designs  of  delicate  and  intricate  workmanship,  but  are  of 
fair  proportionate  value  to  the  purchasers.  What  is  called  standarc  or  guinea 
gold  is  made  of  twenty-two  parts  pure  gold  and  two  of  alloy.  Of  this  quality 
gold  coins  are  made. 


CHEMIST R  V 


“  The  relative  values  are  as  follows : 


£ 

5. 

d 

£ 

/. 

d. 

22-carat  gold  is  worth 

3 

17 

io| 

per  oz. 

8-carat  gold  is  worth  1 

8 

3f  per  oz. 

18 

99 

3 

3 

8| 

99 

6 

99 

99 

I 

1 

ry  1 

iJ 

16  „ 

99 

2 

16 

7§ 

99 

4 

99 

99 

O 

14 

2  „ 

14 

97 

2 

9 

6\ 

99 

2 

99 

99 

O 

7 

I 

10  „ 

99 

1 

15 

4i 

99 

1 

99 

99 

O 

3 

6  „ 

9 

99 

1 

1 1 

10 

99 

*  “  Until  the  reign  of  George  the  Third  the  standard  of  gold  was  fixed  at 

22  carats,  that  is,  of  twenty-two  parts  of  the  pure  metal  and  two  of  alloy. 
This  was  the  quality  of  the  gold  coin.  At  that  time  also  goldsmiths  were 
bound  by  law  to  make  no  ‘  vessel  or  ware’  save  of  the  standard.  During  this 
reign,  however,  an  Act  of  Parliament  was  passed  permitting  a  lower  stan¬ 
dard,  viz.,  1 8  carats  (or  eighteen  parts  pure  gold  and  six  alloy),  to  be  used  in 
the  manufacture  of  gold  ornaments  or  jewellery ;  and,  in  order  that  the  public 
might  be  protected  against  fraud,  the  Legislature  conferred  upon  the  Gold¬ 
smiths’  Company  power  to  examine  the  quality  of  gold  in  course  of  manufac¬ 
ture  found  in  the  different  workshops ;  to  break  up  all  that  was  of  an  inferior 
kind ;  and  to  punish  the  offenders  by  fines.  The  said  Company  was  also 
authorized  to  compel  manufacturers  to  bring  their  articles  to  the  Hall  to  be 
assayed  and  stamped  according  to  their  quality  or  value. 

“  After  a  while,  however,  exceptions  to  this  rule  were  made,  and  a  compul¬ 
sory  mark  was  only  required  upon  the  following:  wedding-rings,  22-carat; 
mourning  rings,  18  or  22-carat;  watch-cases,  from  9  to  22-carat. 

“  Thus  it  soon  became  the  practice  to  manufacture  other  articles  in  gold  of 
a  most  inferior  quality,  so  that  at  present  it  is  impossible  without  the  guarantee 
of  a  respectable  jeweller  to  know  what  you  are  buying.” 

Gold  does  not  tarnish  when  exposed  to  damp  or  dry  air:  the  dust  and  dirt 
which  collect  on  gilt  iron  railings  suggests  the  idea  that  the  gold  itself  is 
affected ;  but  this  is  not  the  case,  as  even  sulphur,  which  blackens  silver  so 
quickly  in  London  and  other  large  cities,  has  no  power  to  alter  the  surface  of 
gold. 

There  are  two  compounds  of  gold  and  oxygen :  the  aurous  oxide  or  sub¬ 
oxide  of  gold  (Au20),  and  the  auric  oxide  or  peroxide  (Au203). 

The  salts  of  gold  worthy  of  note  are  the  sulphide  of  gold  (Au*St);  the  two 
chlorides  of  gold,  the  protochloride  (AuCl)  and  the  trichloride  (AuClj),  and 
the  hydrated  double  stannate  of  gold  and  tin,  or  “ purple  of  Cassius”  (SnAu* 
Sn206r  4H20),  used  to  impart  the  ruby  red  to  glass  and  the  rose  colour  to 
porcelain. 


ORGANIC  CHEMISTRY. 

FROM  the  air,  water,  and  various  natural  substances  contained  in  the  earth, 
we  derive  all  the  bodies  that  have  been  discussed  in  the  list  of  non- 
metallic  and  metallic  elements.  These  elements  have  been  spoken  of  as  it 
they  belonged  only  to  dead  matter:  it  is,  however,  clear  that  some  of  these 
elements  are  operated  upon,  and  are  only  built  up  into  complex  organic  com¬ 
pounds,  by  the  influence  of  vitality.  Thus  it  is  we  have  organized  matter,  such 
as  woody  fibre,  cellulin,  bone,  muscle,  and  nerve  matter.  All  these  things 
have  been  connected  with  life:  the  chemist  could  not  take  the  elements  of 
which  they  are  composed  and  put  them  together  again,  to  re-form  muscle  or 
nerve  matter.  Analysis,  but  not  synthesis,  is  the  ruling  power  in  organic 
chemistry.  There  are,  however,  organic  compounds  that  will  crystallize,  and 
which  possess  a  constant  and  exact  composition,  and  yet  it  cannot  be  said 
they  are  organized. 

The  alkaloids  of  the  cinchonas,  or  those  contained  in  opium,  oxalic  acid, 
sugar,  the  alkaloids  of  coffee,  tea,  chocolate,  are  all  examples  of  organic  com¬ 
pounds,  although  they  do  not  betray  any  organic  structure  such  as  would  be 
seen  with  the  aid  of  a  microscope  in  the  various  tissues  or  parts  of  a  living 
animal  or  plant. 

The  field  of  inquiry  included  under  the  head  of  organic  chemistry  is,  there¬ 
fore,  of  vast  extent :  it  not  only  treats  of  the  nutrition  of  animals  and  vege¬ 
tables,  but  discusses  elaborately  the  solids  and  fluids  and  bases  of  animal 
origin.  It  analyses  and  discovers  the  nature  and  properties  of  resins,  gums, 
colouring  matter,  essential  oils,  essences,  the  alkaloids,  the  fatty  and  vegetable 
acids,  and  organic  acids  in  general;  products  obtained  from  sugar,  alcohol, 
glycerine;  the  ethers;  and  all  the  interesting  changes  brought  about  by  fer¬ 
mentation.  In  the  limited  space  at  our  command  the  analysis  of  organic 
bodies  only  can  be  briefly  alluded  to.  In  the  analysis  of  an  inorganic  salt, 
such  as  cupric  sulphate,  it  is  always  usual  to  speak  of  the  proximate  and 
ultimate  constituents:  the  proximate  constituents  would  be  oxide  of  copper, 
sulphuric  acid,  and  water;  the  ultimate  elements,  copper,  oxygen,  sulphur 
and  hydrogen.  So  it  is  with  organic  compounds :  the  coffee-berry  consists 
(according  to  Payen)  of  the  following  proximate  constituents: 

Ligneous  tissue  Compound  of  caffeine  with  potash  and 

Hygroscopic  water  chlorogenic  (catfeic)  acid 

Fixed  fatty  matter  Aromatic  essential  oil 

Gum,  sugar,  and  a  vegetable  acid  Solid  fatty  essence 
Azotized  matter  analogous  to  legumine  Saline  matters. 

Free  caffeine 

The  whole  reduced  to  ultimate  elements  would  be  represented  by  carbon, 
oxygen,  hydrogen,  nitrogen,  potassium,  and  phosphorus. 


712 


ORGANIC  CHEMISTR  Y 


The  analysis  of  an  organic  body  is,  therefore,  commenced  by  a  careful 
separation  of  each  proximate  constituent,  and  these  are  subjected  to  a  separate 
investigation  with  respect  to  their  individual  properties,  and  finally  to  an  ulti¬ 
mate  analysis.  The  organic  substance  must  be  carefully  dried,  and,  of  course, 
should  be  free  from  all  impurity  or  admixture  with  any  other  organic  body  ; 
and  as  the  ultimate  composition  can  only  be  obtained  by  its  so-called  “destruc¬ 
tion,”  or  rather  combustion,  the  material  (say  sugar)  is  placed  in  a  glass  tube 
of  hard  Bohemian  glass,  15  in.  long  and  |  in.  in  diameter,  as  marked  D,  E,  F, 
in  Fig.  531,  and  this  is  laid  in  a  sheet-iron  trough  or  furnace,  A  B,  in  which  red- 
hot  charcoal  is  carefully  placed.  If  sugar  alone  were  put  in  the  tube,  destruc¬ 
tive  distillation  only  would  take  place,  and  the  ultimate  analysis  could  not  be 
carried  out  to  the  end  ;  it  is  usual,  therefore,  to  mix  with  the  organic  substance 
some  material  that  will  afford  oxygen.  The  body  usually  employed  for  this 


Fig.  531. — Apparatus  for  Organic  Analysis. 

purpose  is  oxide  of  copper,  and  numerous  precautions  are  taken  not  only  in 
weighing  out  the  dried  substance  under  examination,  but  in  mixing  it  with 
the  oxide  of  copper,  and  finally  placing  it  into  the  combustion-tube. 

Sugar  consists  of  carbon,  oxygen,  and  hydrogen,  and  is  resolved  into  water 
and  carbonic  acid  when  heated  with  oxide  of  copper.  To  separate  the  water, 
the  glass  bulb  C,  with  a  tube  containing  chloride  of  calcium,  is  attached  to  the 
combustion-tube,  and  receives  and  retains  the  water,  whilst  the  carbonic  acid 
is  absorbed  by  a  solution  of  potash  of  a  specific  gravity  of  from  1*25  to  i'27 
in  the  bulb-tube,  G;  beyond  the  potash  solution  bulb  is  another  tube,  H,  con¬ 
taining  fragments  of  hydrate  of  potash,  which  arrests  any  moisture  and  car¬ 
bonic  acid  that  may  pass  the  dessicating  tube  and  potash  bulbs.  The  careful 
and  patient  weighings  of  the  combustion  tube  against  the  condensing  tube  and 
potash  bulb  supply  data  which  the  chemist  works  into  the  formula  representing 
the  substance  under  examination. 

The  student  who  desires  to  become  a  proficient  in  the  analysis  of  organic 
bodies  should  consult  Dr.  Miller’s  “Elements  of  Chemistry,”  or  Liebig's 
“  Handbook  of  Organic  Analysis,”  and  after  working  upon  sugar  until  his 
figures  are  constant,  he  may  then  go  on  to  the  analysis  of  organic  bodies  con¬ 
taining  nitrogen.  Here  again  another  series  of  precautions  must  be  taken, 
which,  are  fully  described  in  the  works  already  alluded  to. 

In  the  various  kinds  of  organic  analysis  the  ingenuity  of  the  chemist  is  taxed 
to  originate  tubes  ot  different  shapes  to  answer  special  purposes.  (See  Fig. 
532-) 

When  it  is  necessary  to  restore  the  whole  tube  system  used  in  organic 


COMBINATION  OF  ORGANIC  BODIES. 


Fig.  532. —  Tubes  and  Bulbs  that  may  be  employed  in  Oganie  Analysis. 


analysis  to  the  normal  condition,  so  that  each  tube  and  bulb  is  filled  with 
atmospheric  air,  an  aspirator  is  attached.  The  vessel  C,  Fig.  533,  is  called  the 
aspirator,  because  it  sucks  or  draws  the  atmospheric  air  into  the  tubes. 

The  combination  of  organic  bodies  may  also  be  effected  with  pure  oxygen 
gas,  assisted  by  Hoffman’s  furnace,  in  which  the  heat  is  produced  by  burning 
gas.  Forty  years  ago,  the  teacher  (Mr.  John  Thomas  Cooper)  under  whom 
the  writer  studied,  invented  a  very  excellent  apparatus  for  organic  analysis,  in 
which  the  heat  was  produced  by  the  combustion  of  alcohol. 


Fig.  533. 

A,  thecombustion-tube  ;  d.  furnace ;  b,  potash  bulb;  c,  bottle  full  of  water:  whilst  the  latter  runs  out,  air 
must  pass  through  the  various  tubes,  and  as  they  were  weighed  in  the  titst  place  when  they  contained 
air,  so  the  last  weighing  would  be  incorrect  unless  the  various  tubes  contained  the  same  gaseous 

med.um. 

The  facts  supplied  by  the  careful  and  plodding  experiments  of  numerous 
chemists  in  organic  chemistry  have  supplied  Laurent,  Liebig,  Gerhardt,  and 
their  followers  with  the  facts  which  have  created  a  new  nomenclature  in  organic 
chemistry,  extending  to  the  whole  range  of  chemical  science,  inorganic  as  well 
as  organic. 

Contributions  to.  and  knowledge  of,  organic  decomposition  are  always  valu¬ 
able;  and  as  a  sequel  to  this  brief  article  may  be  noticed  the  curious  experi¬ 
ments  lately  made  by  Dr.  B.  Richardson,  f.R.S.,  which  are  fully  detailed  in 
the  “  Medical  Times  and  Gazette,”  9th  January,  1869,  as  follows: 


7  x4 


ORGANIC  CHEMISTRY. 


Exposure  of  Animal  Substances  to  Water  Gas  at  a  High 

Temperature — 340°  F. 

The  learned  author  says  : 

“  I  woke  one  day  not  long  since  from  sleep  with  a  dream  before  me  in  won¬ 
derful  reality.  I  thought  I  had  been  at  work  in  the  laboratory  subjecting 
animal  structures  to  the  same  process  as  that  to  which  the  dentist  subjects 
vulcanized  india-rubber  when  he  is  making  vulcanite  base.  The  dream, 
childish  as  it  was,  as  coming  from  no  traceable  line  of  connected  thought, 
seemed  to  me  to  be  worth  accepting  as  a  hint  to  positive  work,  and  so  I  fol¬ 
lowed  up  the  ideal  by  the  real,  with  results  which  1  propose  to  describe  to-day 
as  simply  as  1  have  read  them. 

“  We  take  for  our  purpose  the  common  vulcanizing  apparatus  used  by  the 
dentist,  and  depicted  in  the  diagram  (Fig  534).  It  is  a  very  strong  chamber 


Fig.  535. 

a,  Mask  ready  for  filling;  b,  loose  lid;  c,  encircling 
band,  with  compressing-screws. 


a,  iron  cylinder;  b,  stove;  c,  gas  burner;  d,  lid  with  safety-valve;  e,  thermometer. 


of  iron,  enclosed  in  an  iron  case  or  stove,  with  a  series  of  gas  burners  at  the 
iower  part  of  the  stove.  The  iron  chamber,  which  receives  the  substances  to 
be  operated  upon,  is  heated  by  the  burners.  It  is  furnished  with  a  heavy  iron 
lid  with  binding-screws,  a  safety-valve,  and  a  tube  for  holding  mercury,  in 
which  a  thermometer  is  Inserted.  When  we  are  about  to  use  the  apparatus, 
we  place  our  specimens  in  the  chamber  with  a  little  water.  The  apparatus 
I  have  used,  and  which  has  been  kindly  lent  me  by  my  good  friend  and 


DR.  RICHARDSON'S  EXPERIMENTS. 


7i5 


neighbour,  Mr.  Ballard,  has  a  chamber  10  inches  deep  and  5  inches  in  dia¬ 
meter.  Six  or  eight  fluid  ounces  of  water  in  the  chamber  answer  very  well 
for  one  series  of  experiments;  but  the  quantity  may  be  varied,  by  which  dif¬ 
ferent  results  may  be  obtained.  Having,  then,  placed  our  specimens  and  the 
water  in  the  iron  chamber,  we  screw  on  the  lid  firmly,  interposing  what  may 
be  called  a  washer  of  brown  paper  between  the  lid  and  the  chamber  at  the 
part  where  they  touch  ;  we  screw  down  the  safety-valve,  interposing  beween  it 
and  the  small  opening  it  covers  also  a  layer  of  brown  paper;  we  put  the  ther¬ 
mometer  into  the  mercury,  light  the  gas,  and  watch  the  rise  in  the  ther¬ 
mometer  up  to  the  point  of  heat  required.  The  necessary  degree  of  heat 
obtained,  the  gas  is  turned  a  little  down  and  moderated  until  the  mercury 
remains  steadily  at  one  point,  and  the  experiment  is  continued  for  whatever 
length  of  time  may  be  desired. 

“The  specimens  of  animal  structures  to  be  experimented  on  may  be  intro¬ 
duced  into  the  chamber  in  different  ways.  In  some  cases  we  place  the  speci¬ 
men  directly  in  the  chamber  in  or  above  the  water ;  in  other  cases  we  put  it 
in  an  iron  flask  filled  with  wet  plaster  of  Paris,  lime,  carbonate  of  lime,  pow¬ 
dered  carbon,  clay,  powdered  Portland  stone,  or  other  substance,  and  subject 
the  whole  to  pressure  by  compressing-screws.  1  have  constructed  a  very 
convenient  iron  flask  for  this  purpose.  It  consists  of  a  framework  of  iron, 
with  two  plates  of  iron  to  make  a  false  top  and  bottom.  The  frame  laid  on 
the  lower  plate  forms  a  flask,  and  into  it  the  plaster  of  Paris,  or  clay,  or  sand, 
or  carbon,  moistened  with  water,  is  placed,  with  the  specimen  embedded. 
Then  the  upper  plate  of  iron  is  dropped  on,  an  encircling  band  of  iron  is 
passed  over  the  whole  lengthways,  two  screws  in  this  band  are  brought  forcibly 
down  on  the  upper  plate  of  the  box,  and  thus  the  specimen,  with  the  substance 
in  which  it  is  buried,  is  firmly  encased.  The  iron  flask,  in  this  way  arranged, 
is  now  ready  to  be  placed  in  the  chamber.  1  he  advantage  of  this  flask  is, 
that  when  the  exposure  to  heat  is  completed  and  the  metal  is  cooled  down,  on 
setting  free  the  iron  band  the  false  top  and  bottom  can  be  removed,  and  the 
specimen  can  be  cut  out  with  a  small  keyhole-saw  from  its  iron  framework. 
The  flask  is  depicted  in  the  diagram  (Fig.  535)  in  parts. 

“  Having  stated  these  preliminaries,  1  pass  to  describe  some  of  the  results 
which  up  to  this  time  have  been  obtained. 


“  BLOOD. 

“  Into  the  chamber  of  the  apparatus  a  portion  of  blood-clot,  from  the  blood 
of  an  ox,  was  placed  on  a  shelf  with  8  oz.  of  water  beneath.  I  he  lid  of  the 
chamber  was  firmly  adjusted,  the  heat  was  raised  to  34°J  F .,  and  was  sustained 
at  that  degree  for  one  hour  and  a  half.  The  heat  was  then  withdrawn,  and 
some  hours  were  allowed  for  cooling.  On  opening  the  iron  chambci,  the  )  00 
was  found  almost  unaltered  in  shape,  but  altogether  changed  in  consistence 
and  structure.  It  felt  like  simple  caoutchouc,  but  broke  with  a  bright  surface 
like  Spanish  liquorice.  The  natural  characteristics  of  the  blood  were  lost,  and 
on  irentle  drying  the  mass  became  brittle,  closely  resembling  jet.  A  specimen 
of  blood  thus  treated  has  been  examined  bv  mv  friend  Dr.  Sedgwick,  w  ho 
reports  upon,  it  that  it  ‘was  a  bright  black,  friable,  jet-like  material.  Gentlv 
rubbed  down  with  a  little  distilled  water,  it  formed  a  reddish-brown  thud,  wliic  ■ 
under  the  microscope  was  seen  to  consist  of  a  coloured  liquid,  and  reddish 
granular  masses  of  various  sizes.  Very  many  were  about  one-sixth  the  size 
of  a  blood  corpuscle,  reddish-brown,  and  very  irregular  in  shape.  As  the 


ORGANIC  CHEMISTRY. 


716 


solution  dried,  one  or  two  irregularly  hexagonal  crystals  made  their  appear¬ 
ance.  The  substance,  after  twenty-four  hours’  soaking,  was  partially  soluble 
in  strong  solution  of  ammonia,  very  slightly  in  distilled  water,  and  hardly  at 
all  in  dilute  hydrochloric  acid  and  in  methylic  alcohol;  it  was  untouched  in 
ethylic  ether  and  in  chloroform.’ 

“  Into  the  iron  box  or  flask  plaster  of  Paris  was  poured  in  the  fluid  state,  and 
a  clot  of  fresh  blood  was  immersed  in  the  plaster.  The  lid  was  placed  on  the 
box,  and  when  the  plaster  had  set  firmly,  the  whole  was  placed  in  the  chamber 
with  6  oz.  of  water.  The  temperature  was  raised  to  340°,  and  sustained  for  an 
hour  and  a  half.  On  breaking  up  the  plaster,  after  cooling,  the  blood  was  found 
in  the  same  state  as  that  named  in  the  experiment  described  above. 

“ALBUMEN. 

“An  egg  was  placed  in  the  iron  flask  and  surrounded  with  plaster  of  Paris 
in  the  fluid  condition.  When  the  plaster  was  entirely  set,  the  flask  was  put 
into  the  chamber  with  6  oz.  of  water,  the  temperature  was  raised  to  340°,  and 
was  sustained  for  an  hour  and  a  half.  After  cooling,  which  was  very  rapidly 
effected  by  immersing  the  flask  in  cold  water,  I  found,  on  removing  the  egg, 
that  the  shell  was  nearly  full  of  a  beautiful  transparent  golden  or  amber- 
coloured  fluid,  very  thin,  and  running  like  dissolved  gelatine.  In  the  course 
of  a  few  hours  this  fluid  was  slightly  gelatinized.  The  membrane  lining  the 
shell  was  detached,  but  not  destroyed ;  the  shell  was  dry,  brittle,  and  firmly 
attached  to  the  surrounding  plaster.  The  experiment  was  repeated  with 
another  egg,  but  was  modified  by  allowing  the  apparatus  to  cool  very  slowly 
in  the  air  at  6o°.  On  breaking  the  plaster,  and  cutting  through  the  egg,  no 
fluid  was  found,  but  in  the  centre  a  soft  yellow  substance  (probably  the  yolk), 
about  the  size  of  a  hazel  nut,  and  slightly  glistening  on  the  surface.  On  gently 
drying  this  substance,  it  became  firm,  retaining  its  colour,  and  looking  like 
amber,  but  not  so  hard. 

“the  body  of  a  toad  in  carbon. 

“The  iron  flask  was  partly  filled  with  fluid  plaster  of  Paris.  On  this  layer 
a  bed  of  vegetable  carbon,  in  fine  powder,  was  laid,  and  the  body  of  a  toad 
recently  dead  was  buried  in  it.  The  carbon  mound  was  next  enclosed  in 
plaster;  the  flask  was  closed,  and  half  an  hour  later  it  was  placed  in  the  iron 
chamber  with  10  oz.  of  water.  The  temperature  was  first  raised  to  350°  F., 
but  was  brought  down  to  340°,  and  was  retained  at  this  degree  for  an  hour 
and  forty  minutes.  The  gas  was  then  turned  off,  and  the  apparatus  was  allowed 
to  cool  slowly.  On  opening  the  flask,  the  body  of  the  animal  was  found  to  be 
altogether  destroyed,  and  so  mixed  with  the  carbon  that  no  part  of  it  could 
be  defined. 

“the  body  of  a  frog  in  sand. 

“  The  body  of  a  frog  recently  dead  was  buried  within  the  iron  flask,  in  moist 
fine  sand  compressed  with  moderate  firmness.  The  flask  was  then  put  into 
the  iron  chamber,  with  6  oz.  of  water,  and  the  temperature  was  raised  to  340° 
F.,  and  sustained  for  an  hour  and  a  half.  The  flask  was  opened  twelve  hours 
afterwards,  and  the  results  of  the  experiment  were  found  to  be  nearly  the 
same  as  when  carbon  was  employed.  The  animal  was  destroyed,  and  no  dis¬ 
tinct  organ  or  structure  could  be  distinguished. 


DR.  RICHARDSON'S  EXPERIMENTS. 


BODY  OF  A  FROG  IN  PLASTER  OF  PARIS. 

“  Fluid  plaster  of  Paris  was  poured  into  the  iron  flask  until  the  flask  was 
half  full.  The  body  of  a  frog  recently  dead  was  now  laid  on  the  plaster,  and 
allowed  to  mould  itself  to  it.  When  the  plaster  had  become  rather  firm, 
another  quantity  ol  fluid  plaster  was  poured  in,  so  as  to  bury  the  frog  com¬ 
pletely  and  fill  the  flask.  An  hour  later,  the  flask,  which  had  been  closed  with 
pressure,  was  placed  in  the  iron  chamber.  The  temperature  was  raised  to 
34°°  h .,  and  sustained  for  two  hours.  Twelve  hours  later  the  flask  was 
opened,  and  a  mould  ot  the  frog  was  found,  the  organic  soft  parts  of  the  body 
having  been  destroyed.  At  the  lower  part,  in  the  centre,  was  a  black  spot: 
the  spot  consisted  of  blood  which  had  gravitated  to  the  lowest  part.  Besides 
this,  there  was  a  little  debris  of  earthy  part  of  bone  within  the  mould.  The 
impression  of  the  body  was  beautifully  marked  in  the  plaster. 

“BODY  OF  A  FISH  IN  PLASTER  AND  ALUM. 

“  Some  plaster  of  Paris,  made  into  a  fluid  with  water  containing  alum  in 
solution,  was  poured  into  an  iron  flask  until  the  flask  was  half  filled.  The 
body  of  a  dead  fish,  a  common  sprat,  was  cut  in  halves  transversely,  the  two 


Fig.  536. — Body  of  a  Fis/i  in  Plaster  and  Alum. 

halves  were  laid  upon  the  plaster,  and  the  flask  was  filled  up  with  fluid  plaster 
and  closed.  When  the  plaster  was  firm,  the  flask  was  placed  in  the  iron 
chamber,  with  4  oz.  of  water,  and  the  temperatuie  was  raised  to  340  F.,  and 
was  sustained  at  that  degree  for  an  hour.  I  wclve  hours  afterwards  the  flask 
was  laid  open,  and  the  plaster  cut  in  halves,  when  two  moulds  were  found,  one 
of  the  upper,  the  other  of  the  lower  half  of  the  fish.  1  he  markings  ot  the 
body  of  the  fish  were  delineated  on  the  mould  ;  a  small  portion  of  bone  spinal) 
was  left;  a  dark-coloured  fine  spot,  surrounded  by  a  shiny  scalv  substance, 
indicated  the  position  of  the  eyeball ;  a  little  filamentous  debris  remained, 
consisting  probably  of  the  scaly  covering  of  the  animal. 


7x8 


CONCLUSION. 


Fig.  537. — Oyster-shell  subjected  to  same  process. 


After  perusing  the  account  of  Dr.  Richardson’s  experiments,  the  mind 
reverts  to  the  formation  of  natural  fossils,  and  the  remarkable  imitation  of 
nature  with  pressure  and  heat,  which  produces  these  qtiasi-i ossil  moulds  in 
plaster  of  Paris.  Fossils  have  been  spoken  of  as  “the  medals  of  creation;” 
who  would  dare  (unless  they  were  makers  of  artificial  flint-head  arrows)  to 
imitate  so  closely?  But  the  forgery  in  this  case  is  an  advance  in  science, 
and  no  doubt  will  assist  the  geologist  and  palaeontologist  to  make  speculations 
(this  time)  founded  on  actual  experiment.  In  bringing  this  work  to  a  con¬ 
clusion,  the  writer  desires  it  to  be  understood  that  he  has  endeavoured  to  fulfil 
a  promise  made  in  his  first  elementary  work  on  science,  and  that  was,  to  try 
to  lead  the  youthful  and  unlearned  reader  further  on  in  the  pursuit  of  that 
science;  the  beginning  of  which,  Sir  Humphrey  Davy  said,  is  pleasure;  its 
progress  knowledge;  its  objects  truth  and  utility. 

It  is  said  that  Demosthenes  first  conceived  his  passion  for  eloquence  upon 
hearing  the  orator  Callistratus,  and  witnessing  the  applauses  with  which  his 
performance  was  rewarded;  that  Tycho  Brahe  resolved  to  devote  his  life  to 
astronomy  in  consequence  of  his  witnessing,  when  a  child,  an  eclipse  of  the 
sun.  Surely  amongst  the  thousands  of  young  people  who  attend  scientific  lec¬ 
tures,  there  must  be  undeveloped  geniuses  who  might,  if  they  read  and  prac¬ 
tise  scientific  experiments,  become  as  useful  and  as  celebrated  as  a  Davy,  a 
Faraday,  or  a  Wheatstone! 


Index. 


LIGHT. 

Absorption  bands.  Professor  Stokes’s,  tig,  t2o 
Acland  s,  Mr.,  observations  on  defects  of  vi¬ 
sion,  87,  88 

Aluminium  disc,  2,  3,  4 
Analyzation  of  light,  1x4—124 
Apparatus  for  compressing  glass,  143 
Application  of  the  direct  rays  of  the  sun  as  a 
motive  power.  14 
Apps's  induclorium,  29 
Arago's  photometer,  35,  36,  37,  38 
Armatus,  Salvinus,  87 

•  Attraction  and  repulsion  from  radiation,  5 

Babinet,  35 
Barton,  132 
Becquerel,  113 
Bennet,  6 
Bernard,  35 

Biaxial  crystals,  144,  145 
Biot,  M.,  51 
Bird,  Dr.  Golding,  92 
Bologna  stone,  20 
Boyle,  Hon.  Robert,  128 
Brereton,  Lord,  129 

Brewster,  Sir  David,  51,  53,  57,  71,  86,88,92, 
no,  in,  115,  132,  134 
Brewster’s  refracting  stereoscope,  90 
Browning's  description  of  the  silvered  glass 
reflecting  telescopes,  6l,  62,  63 
Brunei,  Mr.,  96 

Bunsen  burner  with  ring-stand,  119 
Bunsen,  115 


Camera  obscura,  77,  78 
Camera  prism,  78 
Canton’s  phosphorus,  20 
Catoptrics,  40 

Caustic  curves,  production  of,  12s,  126 
Cellini,  79,  80 
Chadburn’s  lantern,  80,  81 
Charcoal  crucibles,  122, 123 
Chemical  combination  a  source  of  light,  30 
Chromatic  aberration,  126,  127 
Colouis  of  thin  plates,  128,  129,  132,  133 
Complementary  colours  overlapping  and  form¬ 
ing  white  light,  127 


BIG  H  T — continued. 

Concave  mirror  showing  the  aberration  of 
rays  of  light,  125 

Convergent  ray's  of  light,  41,  42,  43 
Corpuscular  theory  of  light,  1,  2,  129 
Cowper,  Professor,  92 

Crookes’s  test  lamp-wick  and  photometer,  34, 
35 


Daguerre,  process  of,  20 
Daniell,  Professor,  115 
Darker’s  kaleidoscope,  53,  54,  53 
Darkness,  2,  125,  132 
Decomposition  of  light,  106,  107,  111 
De  la  Rue,  129 

Descartes,  1,  69  ;  his  laws,  69,  70 

Diffusion  of  light,  33 — 40 

Dioptrics,  69 

Dispersion  of  light,  106 

Dissolvjng  view  arrangement  by  Mr.  Child,  79 

Dissolving  views  at  the  Polytechnic,  81 

Divergent  rays  of  light,  41,  42,  43 

Dolland,  126 

Double  refraction,  133,  134,  133 
Duboscq,  Soleil,  94 

Eidotrope,  the,  133 

Electric  spark,  the,  21,  25,  114,  its 

Emission  theory,  6 

Equality  of  illumination,  how  obtained,  38,39 

Ether,  x,  2,  4,  7(  17,  19 . 

Experiments  with  blacked  aluminium  disc, 
without  rock  salt,  4 
Experiments  with  vibrating  strings,  17 
Extraordinary'  rays  of  light,  133 
Eyre,  the  human,  84 — 88 

-  description  and  diagrams,  84,  85 

-  refractive  powers,  86  ;  artificial  aids  to 

sight,  87,  88 


Faraday,  Professor,  93,  104 
Fenian  fire,  31 
Fits  of  reflection,  129,  132 
Fits  of  transmission,  129,  132 
Flame  in  centre  of  a  circle  throwing  out  ray's 
in  every'  direction,  33 


713 


720 


INDEX. 


LIGHT  - continued . 

Fluid  friction,  5 
Fluorescence,  114 
Frankland,  Dr.,  35 
Franklin,  Dr.,  2 
Ftauenhofer,  113,  114,  132 
Fresnel’s  arrangement  to  show  the  interfer¬ 
ence  of  the  waves  of  light,  131 


Ganot’s  “  Physics,”  69 
Gassiot,  1 1 7,  118 

“  Ghost  ”  illusions,  description  and  explana¬ 
tion,  43—51 

Glass,  apparatus  for  compressing,  143 
Glass  specula,  65,  66 
Glass,  unannealed,  143 
Gmelin,  21 

Goddard’s  apparatus  and  experiments  on  the 
polarization  of  light,  136 — 142 
Graham,  5 
Greek  fire,  31 


Hall,  126 
Halley,  131 

Heat  a  source  of  light,  2J,  32 
Heavy  spar,  20 
Heliostat,  the,  107,  131 

Herschel  -  Browning  direct  -  vision  spectro¬ 
scope,  the,  1 16 

Herschel’s  direct-vision  prism,  112 
Herschel,  Sir  John,  67,  113,  116 
Herschel’s  table  of  the  colours  of  thin  plates 
of  air,  133 

Highley’s  dissolving  view  apparatus,  81,  82, 

83 

Hook,  1,  128 
Huggins,  115,  t22,  123 
Huygens,  i,  134 


Iceland  spar,  a  rhomb  ot,  showing  the  double 
refraction  of  light,  134 

Illusory  effects  produced  by  the  reflection  of 
light  from  the  surface  of  glass,  43  51,  59, 

60 

Images  formed  by  silvered  mirrors,  47 — 51 
Incandescence,  21 
Incident  rays  of  light,  40,  69 
Indices  of  refraction,  table  of  the,  72 
Induction  coil  at  Polytechnic,  22 — 27 
Inductorium,  Apps’s,  29 
Instrument  used  by  Newton  to  obtain  the 
rings  of  colour  from  thin  plates  of  air,  128 
Intensity  of  waves  doubled  by  superposition 
and  coincidence  of  two  equal  systems,  130 
Interference  of  light,  128 — 133 


Japanese  magic  mirror,  the,  55 


Kaleidoscope,  the,  51—55 
Kerr,  134 

Key’s,  Rev.  Cooper,  process  for  figuring  spe¬ 
cula,  62 
Kircher,  78 

Kirchoff,  115,  119,  122,  123,  230 
Knight,  the,  watching  his  armour,  44 


L  I  G  H  T — continued. 

La  boite  magique,  59 
Lenses,  achromatic,  106 

-  Dolland’s  and  Blair’s,  126 

-  Forms  of — spherical,  plano-convex, 

plano-concave,  meniscus,  concavo-convex, 
74,  75 

L]ght,  1— 145 

Light  and  colour,  106 — 114 

Light  reflected  from  transparent  substances, 

•43 

Light  the  frequent  attendant  of  electrical 
phenomena,  21 
Luminous  bodies,  21,  32,  33 


Magic  lantern,  the,  78 
Malus,  135 

Margraf,  process  of,  20 
Materiality  of  light,  2 
Maxwell,  5 

Mechanical  force  a  source  of  light,  31 
Melville,  Thomas,  115 
Microscope,  the,  simple  and  compound,  75 
Micro-spectroscope,  Sorby  and  Browning’s, 

120 

Miller,  Professor,  115,  123 
Mitchell,  2 

Models  of  fixed  waves  of  light,  129,  130 
Modern  Delphic  Oracle,  the,  49 
Modifications  light  may  undergo,  40 
Monochromatic  lamp  and  light,  115 
Moser,  1 13 
Muschenbroek,  87 


Newton,  1,  2,  106,  in,  126,  128,  129,  131,  134, 
144 

Nicol’s  prism,  127,  140,  141 
Nostrodamus  and  Marie  de  Medicis,  59 


Oersted,  21 
Opacity,  32 
Opalescence,  32 

Optical  instruments  whose  properties  depend 
on  refraction,  75 — 84 
Ordinary  rays  of  light,  133 
Otheoscope,  the,  5,  16 

Oxy-hydrogen  kaleidoscope,  the,  53,  54,  55 
Oxy-hydrogen  polariscope,  the,  139 — 142 


Parallel  rays  of  light,  41,  72,  73,  74 
Parallel  rays  falling  on  a  concave  mirror,  41 
Parallel  rays  reflected  from  a  convex  mirror, 
42 

Pans,  Dr  ,  94 

Persistence  of  vision,  91 — 106 
Phantoscope,  the,  43 
Phenakistiscope,  the,  94 
Phosphoregenic  rays,  113 
Phosphorescence,  T9,  IT3 
Phosphorescence  of  bodies,  5,  ao,  31,  113 
Phosphorescent  tubes,  20 
Phosphori,  20 
Phosphoroscope,  the,  113 
Photodrome,  the,  104,  105 
Photography,  T13 
Photometers,  33,  34,  35,  36,  37,  38 


INDEX. 


721 


LI  G  H  T — continued. 

Plateau,  94,  105 

Polariscope,  the  oxy-hydrogen,  139 
Polarity,  135 

Polarization  by  reflection  and  simple  refrac¬ 
tion,  136 

Polarization  by  the  tourmaline,  138 
Polarization  of  light,  133— 145 
Polarized  light,  34,  133 — 145 
Porta,  Baptista,  77 
Prinseps,  James,  57 

Prism,  the;  Brewster’s  instructions,  71,  72 
Propagation  of  light,  1,  5,  19,  69,  134 
“  Proteus,”  47 


Radiometer,  Crookes’s,  5 
Radiometer,  the,  12 — 16,  30 
Rays  of  light,  40,  41 
Real  existence  of  ether,  2 
Recomposition  of  light,  nc 
Redi,  Francisco,  86 
Reflected  rays  of  light,  40 
Reflection  of  light,  1,  32,  40 — 68 
Reflection  of  light  from  transparent  sub¬ 
stances,  42 

Reflection  of  parallel  or  equi-distant  rays,  41  J 
Refracted  rays  of  light,  40,  69 
Refracting  telescope,  arrangement  of  the 
lenses  in  a,  127 

Refraction,  a  demonstration  of  the  property 
of,  69 

Refraction  of  light,  1,  40,  69 — 83 
Refraction  of  light  through  plane  glass,  73 
Refraction  of  parallel  rays  by  concave  sur¬ 
faces,  74 

Redaction  of  parallel  rays  by  convex  surfaces, 

73  . 

Refractive  power,  70 

Repulsion  resulting  from  radiation,  12,  14 
Ritchie's  photometer,  34 
Ritter,  113 
Robertson,  E.  J.,  59 
Robertson's  apparatus  for  “ghost,"  51 
Rogct,  Dr.,  96,  97 
Rose,  Mr.  Thomas,  95 
Rose's  photodrome,  104,  105 
Rosse’s,  Lord,  machine  for  figuring  specula,  , 
67,  68 

Rotation  in  vacuo,  2,  3,  4,  5 


Selenite  slides,  140 
Shadow  Blondin,  the,  31 
Silbermann.  10S 

Silvered  chain  and  electric  light,  iS 
Silvered  cord  vibrating,  18 
Silvered  glass  reflecting  telescopes,  61 — 68 
Simms's  spectrum  apparatus,  115 
Solar  spectrum,  to  obtain  the  ;  apparatus  for 
reflecting  the  seven  colours ;  Brewster  s 
theory  and  experiments,  109,  no,  111,  m 
Solar  spectrum,  dark  or  fixed  lines  in  the  ; 

Frauenhofer’s  seven  lines,  92,  123 
Sources  of  light,  16,  19 — 33 
Spectacles,  86,  87,  88 
Spectroscope,  the,  43,  116,  117,  118,  124 
Spectrum,  physical  properties  of  the,  113 
Spectrum  to  obtain  the  bright  lines  given  by 
any  substance,  117 


LIGH  T — continued. 

Specula,  figuring  and  mounting  ;  the  alt-azi¬ 
muth  stand,  62,  63,  64 

Specula,  to  silver  glass ;  to  prepare,  clean, 
immerse,  and  separate  the  speculum  from 
the  block,  65,  66 

Specula,  on  working  glass,  66,  67,  68 
Spherical  aberration,  125,  126 
Spina,  Alexander  de,  87 
Spottiswoode,  Mr.  William,  27,  i4t 
Sprengel  pump,  7,  8,  9,  10,  13 
Star  spectroscope,  the,  124 
Stereoscope,  the,  88 
Stewart,  Balfour,  2,  6 
Stokes,  Professor,  114,  115,  119 
Stoney,  Mr.  Johnstone,  14 
Stroutian  phosphorus,  20 


Table  of  the  indices  of  refraction,  72 

Tait,  Professor  P.  G.,  2 

Talbot,  Mr.  Fox,  116 

Telescope,  the  compound,  76 

Telescopes,  silvered  glass  reflecting,  61 — 63 

Test  candles  used  in  photometry,  34 

Thallium,  122 

Thaumatrope,  the,  94 

Thermo-electric  pile,  the,  3,  4 

Thompson’s  reflecting  galvanometer  needle,  3 

Thornbury,  2 

Tourmaline,  the,  138 

Transparency,  32 

Transversal  vibrations  of  light,  134,  145 
Tyndall,  17,  113 


Unannealed  glass,  144 

Undulatory  theory,  2,  6,  17,  19,  133,  134,  138 
Uniaxial  crystals,  144 


Vacuum,  1,  2,  5,  7 

Vision,  persistence  of ;  example  of  the  zigzag 
path  of  lightning;  the  spectre  wafer;  ex¬ 
periments  with  the  cog-wheel  apparatus, 
91  — 106 

Vulcanized  tube  thrown  into  protuberance,  17 


Waves  neutralized  by  the  superposition  and 
interference  of  two  equal  systems,  130 
Wheatstone's  reflecting  stereoscope,  88 
Wheatstone,  Sir  Charles,  88,  94,  95,  115,  133 
Whewell’s  definition  of  polarity,  135 
With's,  Mr.  G.,  process  for  figuring  specula, 
62 

Wollaston,  Dr.,  113.  114,  134  . 

Woodward’s  diagrams,  exhibiting  at  one  view 
polarization,  analyzation,  and  interference 
of  light,  145 

Woodumrd's  models  of  waves  with  movable 
rods,  129 


Young,  Dr.,  131,  132,  133,  134 


Zoetrope,  the,  94 


46 


722 


IJSD  EX. 


HEAT. 

Absorptive  power  of  bodies,  226,  227 
Actual  force,  178,  188,  194 
Air  thermometer  of  Sanctorius,  173 
Akin,  Dr.,  230 

Alcohol  or  minimum  thermometer,  directions 
for  determining  the  minimum  temperature 
of  the  air,  162,  163 

Amount  of  expansion  in  solids,  liquids,  and 
gases,  154 

Anderson,  Professor,  210 
Anomaly  of  contraction  of  stretched  or  ex¬ 
panded  caoutchouc  by  heat,  158 
Anomaly  of  expansion  and  contraction  in  one 
body,  156 

Anomaly  of  expansion  and  contraction  in 
water,  156 
Apjohn,  Dr.,  193 

Apparatus  for  determining  elevations  by  the 
temperature  of  the  boiling-point  of  water, 
"9 

Apparatus  for  supplying  water  to  tenders 
whilst  in  motion,  218 
Aqueous  vapour,  169,  191 
Arago,  200,  210 

Athermanous  or  adiathermic  bodies,  228 
Atomic  heat,  187,  189,  194 
Atomic  weight,  194 
Attraction  of  gravity,  188,  190 


Banks,  Sir  Joseph,  183,  186 
Barometrical  thermometer,  199 
Berard,  192 
Bismuth,  157,  176 
Blagden,  Sir  Charles,  153,  184 
Blow-pipe  work  in  Negretti  and  Zambra’s 
thermometer-room,  160 
Boiling-point  of  water,  the,  198,  200 
Boulton,  210,  2ir 
Breguet’s  thermometers,  155 
Brewster,  Sir  David,  183 
Brick  earth,  176 


Caloric,  146,  151,  204,  224 

Capacity  for  heat,  178,  187,  191 

Capacity  for  molecular  motion,  178 

Cast  iron  frame  broken  by  contraction,  154 

Catgut  hygrometer,  222 

Celsius,  160,  161 

Centigrade  scale,  the,  160 

Centrifugal  theory  of  elasticity,  203 

Changes  of  the  state  of  aggregation,  189 

Chantrey,  Sir  Francis,  184 

Chemical  action,  179 

Chemical  equivalent,  194 

Clausius,  188 

Coefficient  of  expansion  of  gases,  the,  170 
Cohesion,  151,  156,  158,  169,  r88,  193 
Combined  steam,  221 
Combined  vapour  engine,  221 
Common  effects  of  heat,  151 
Condensing  engine,  216 
Conduction,  174—187 
Conductivity  of  gases,  183,  186 
Conductivity  of  liquids,  184,  186 
Conductors  of  heat,  good  and  bad,  173,  180 
Congelation,  192 
Conservation  of  energy,  179 


H  E  A  1— continued. 

Convection,  186,  187 

Conversion  of  light  rays  into  heat  rays  by 
change  of  refrangibility,  230 
Conversion  of  potential  into  actual  energy, 
180,  194,  196 

Conversion  of  the  expansion  of  gases  into 
power  or  motion,  171 
Conversion  of  water  into  vapour,  19s 
Cornish  boiler,  the,  220 
Crystallization,  158 
Cylinder  valve  and  condenser,  214 


Dalton,  Dr.,  169,  223 
Daniell,  Professor,  166,  168,  169,  224 
Davy,  Sir  Plumphrey,  149,  170,  226 
Decomposition  of  steam  by  heat  into  oxygen 
and  hydrogen,  179,  201 
De  la  Roche,  192 
De  Luc,  223 

De  Saussure,  198,  199,  223 
Despretz,  176,  177,  186 

Despretz’s  mode  of  determining  the  conduc¬ 
tivity  of  metals,  177 

Diathermanous  or  diathermic  bodies,  228 
Differential  air  thermometer,  174 
Distillation  of  water,  196 
Donny,  M.,  197 

Double-action  engine,  Watt’s,  214,  215 
Double-cylinder  engine,  220 
Drebel,  Cornelius,  173 
Dry  steam,  201 
Dulong,  192,  200 
Du  Trembley,  221 
Dynamic  energy,  188,  190 
Dynamical  theory,  the,  148,  151,  175,  188, 
190,  204 


Ebullition,  r96,  197 
Eccentric,  the,  214 

Elliot’s  models  of  the  locomotive  engine,  217 

Emission,  the  hypothesis  of,  148 

Energy,  178,  188,  194 

Energy  of  the  sun,  148,  149 

Ether,  148,  224 

Evaporation,  193 

Expansion  of  gases  by  heat,  152,  169 — 174 
Expansion  of  liquids  by  heat,  152,  156 — 159 
Expansion  of  mercury  by  heat,  156,  157 
Expansion  of  solids  by  heat,  154 — 156,  168 
Expansion,  to  determine  the  difference  be¬ 
tween  linear,  volume,  and  surface,  156 
Experiment  showing  the  conversion  of  actual 
energy  into  potential  energy,  179 
Experiments  showing  the  bad  conductivity  of 
gases  and  of  water,  183 — 186 
Experiments  with  Mousson’s  apparatus,  195 

Fahrenheit  scale,  the,  160,  161 
Faraday,  Professor,  148,  198,  221,  222 
Faraday’s  experiment — boiling  water  de¬ 
prived  of  air  under  oil  of  turpentine,  197 
Force  and  temperature  of  steam,  table  show¬ 
ing  the,  200,  201 
Force  of  vapour,  223 
Fordyce,  183 
Franklin,  176,  177,  226 


INDEX. 


723 


HE  A  T — continued. 

Franz,  176,  180 
Friction,  149 


Gavesande's  ball  for  showing  the  cubical  ex¬ 
pansion  by  heat,  151 
Gay-Lussac,  169,  203 

Generation  of  heat  by  chemical  action,  149 
Generation  of  heat  by  electrical  action,  149 
Generation  of  heat  by  friction.  149 
Generation  of  heat  by  percussion,  149 
Generation  of  heat  by  vital  power,  150 
’‘Governor,"  the,  215 

Governor  and  throttle  valve  of  Beiliss  and 
Seekings,  216 

Graduation  by  machine  of  the  thermometer 
tubes,  161 

Griffith’s  experiments  illustrating  the  differ¬ 
ence  between  the  conducting  power  of  a 
metal,  an  earth,  and  an  earthy  compound, 

175.  >76 

Ground  ice,  227 
Groves,  Professor,  179,  201 
Gulf  Stream,  the,  187 


Heat,  146 — 234 

Heat  a  mode  of  motion,  169,  178,  189 

Heat  and  light,  148 

Heat  and  power,  148 

Heating  power  of  the  sun,  148,  180 

Heat  of  atoms.  1 86 

Herschel,  Sir  W. ,  230 

High  pressure  engine,  216,  217 

Hope,  Dr  ,  157 

Hornblower,  Jonathan,  220 

Howard's  steam  ploughing  apparatus,  217 

Hygrometry,  222,  223,  224 

Hypothesis  of  molecular  vortices,  the,  205 


Igenhausz,  176,  177 
Inertia  of  heat,  178 
Interior  work  of  heat,  188,  190 
Invisible  heat  rays,  230 


Joule,  Dr.  J.  P..  150,  203 
Joule's  equivalent,  150 


Krupland,  228 


Latent  heat,  187 — 196,  204 
Latent  heat  of  vapour,  201 
Le  Roi,  223 

Leslie,  Sir  John,  173,  226,  227 
Liquefaction,  190,  194,  195 


Marcet's  boiler,  200 
Material  theory  of  caloric,  148,  224 
Maximum  thermometer,  the,  162 
Mayer.  Dr.,  150 
Measures  of  heat,  154 

Mechanical  equivalent  of  heat,  150,  169,  172, 
179,  j88 
Meiloni, 


HE  A  T — continued. 

Melloni’s  apparatus,  229 
Melting-point  of  cast  iron,  the,  168 
Mercury,  156,  157 
Metallic  reflection,  225 

Methods  of  reducing  Fahrenheit’s  scale  to 
the  Centigrade  and  Reaumer’s  scales,  161 
Methods  to  determine  the  specific  heat  of 
bodies,  191,  192 

Methods  to  determine  the  specific  heat  of 
gases,  192 
Molard,  169 

Montgolfier  or  fire  balloon,  153 
Mousson,  195 
Miiller,  230 
Muscular  force,  148 


Negretti  and  Zambra’s  deep-sea  recording 
thermometer,  163 
Newton,  148,  159 
Newton’s  opinion  on  heat,  150 
“  Nonius,”  168 

Norwegian  self-acting  cooking  apparatus,  180 


Odling,  Dr.,  179,  180 


Paddle-wheel  engine,  218 
Papin’s  digester,  201 
Parallel  motion,  the,  215 
Penn,  Messrs.,  221 
Perspiration,  183 
Petit,  192 

Photometer,  the,  191 
Physical  forces,  146 
Platinum,  156 
Playfair,  Professor,  21 1 
Portrait  of  James  Watt,  207 
Possible  energy,  t88 
Potential  heat,  178,  188,  196 
Pouillet,  148 
Pouillet’s  apparatus,  17 a 
Power,  148 

Principle  of  expansion  of  steam,  220 
Progressive  dilatation  of  solids,  table  of  the, 
169 

Proof  that  atmospheric  air  contains  invisible 
steam,  221,  222 
Pyrometer,  the,  166 


Radiating  and  absorbing  powers  of  gases  and 
vapours,  227 
Radiation,  224 — 227 
Radiators,  good  and  bad,  228 
Ramsbottom's  locomotive,  217 
Rankin,  188,  221 
Reaumer's  scale,  160 
Regnault.  M.,  170,  193,  201,  223 
Regnault  s  condensing  hygrometer,  223 
Regnault’s  experiments,  201,  202 
Regular  transitions  of  temperature,  168 
Relation  between  heat  and  mechanical  power, 
150 

Relation  between  radiation,  absorption,  and 
reflection,  226 

Reverse  chemical  action,  180 
Ritchie,  Dr.,  226 


iG - 2 


724 


INDEX. 


H  B  A  T — continued. 

Robertson,  152 
Roebuck,  Dr.,  210,  211 
Rumford,  Count,  149,  150 


Sabine,  Mr.  R.,  147 

Sagredo,  173 

Sensible  heat,  188,  201 

Siberian  exiles  fishing,  158 

Single  cylinder  engines,  220 

Smeaton,  210 

Solander,  Dr.,  183 

Solidification.  158,  195 

Sorensen,  Herr,  181 

Sources  of  heat,  149,  158 

Specific  heat,  177,  187,  189,  ior 

Specific  heat  of  gases  and  vapours,  193 

Specific  heat  of  iron,  192 

Specific  heats  of  equal  weights,  192 

Steam,  148,  190,  196,  199 — 205 

Steam  engine,  the,  207 — 221 

Steam  gas,  221 

Stephenson,  149 

Stewart,  Mr.  B.,  228 

Stokes,  Professor,  230 

Superheated  steam,  221 

Surface  condensation,  220 


Table  of  the  conductive  powers  of  various 
metals,  earths,  and  earthy  compounds,  176 
Table  showing  the  comparative  increase  of 
expansion  of  various  substances  when 
heated,  155 

Tait,  Professor,  163,  205 
Temperature,  170,  187,  191,  223 
Thermo-dynamtcs,  204,  205 
Thermo-electric  pile,  the,  180 
Thermometer,  the,  159,  191 
Thermometric  heat,  147— 154 
Thermometry,  154 
Thompson,  159 
Throttle  valve,  the,  215 


H  E  A  T — continued. 

Tillet,  183 

Time-test  to  determine  the  specific  heat  of 

bodies,  191 

Transmission  of  heat,  228,  229,  230 
Trevithick,  220 
Tribe,  Mr.  Alfred,  158 

Tyndall,  Dr.,  148,  158,  159,  171,  177,  178,  188, 
189,  tc»6,  199,  227,  228,  230 
Tyndall's  apparatus  for  showing  the  heating 
power  of  invisible  rays,  233 
Tyndall’s  diagram,  231 


Undulatory  theory,  the,  148,  149,  151 
Unequal  expansion  of  metals,  155,  156 
Unit  of  work,  the,  150 


Vacuum  engine,  216 
Vacuum,  Torricellian,  222 
Vaporization,  190,  196 
Ventilation,  187 
Vernier,  the,  t68 

Vibratory  nature  of  heat,  150,  170 


Walker’s  description  of  Watt’s  engine  for 
pumping  water  from  mines,  212 
Water,  expansion  and  contraction  of,  157 
Water  power,  148 

Watt,  James;  life  and  inventions,  201,  207 

—215 

Watt’s  double-action  engine,  214 
Wedgwood,  Mr  ,  166,  168 
Wethered,  John,  221 
Wiedemann,  176,  180 
Woolf,  220 

Working  steam  expansively,  218 
Work,  the  unit  of,  150 
Wray,  Mr.  Cecil,  147 


Young,  Dr.,  149,  150,  151 


ELECTRICITY. 

Abel,  Professor,  372 
Arborescence,  344 
Aldini’s  battery,  318 

Aldini's  experiments  in  organic  electricity, 
3U.  318 
Allaman,  277 
Ampere,  360 

Animal  electricity,  315— 319 
Anions,  347,  350 
Anode,  the,  346 

Analogy  between  common  and  voltaic  elec- 
tricity,  324 

Apparatus  for  showing  the  electricity  of 
watery  steam,  307 
Apps  s  battery,  341 


ELECTRICITY  -  continued. 

Armstrong,  Sir  W. ,  302,  306 
Attraction,  237 — 240,  25s,  269 


Babington's  improved  Volta's  "  couronne  de 

t asses,'  333 

Bachoffner,  Dr.,  303,  304 
Baggs’s,  Mr.  Isham,  experiments  with  charged 
Leyden  jars,  283 
Batteries,  on  the  choice  of,  340 
Becquerel,  M.,  243,  244 
Bennet  s  electroscope,  239 
Bohnenberger's  electroscope,  248 
Browning  s  electric  lamp,  373 


INDEX. 


725 


ELECTEICIT  Y — continued. . 

Calorific  effects  of  the  voltaic  current,  365 
Cations.  347,  351 
Cathode,  the,  346 

Cavallo,  Tiberius,  248,  262,  275,  277,  278 
Chaptal,  330 

Charging  and  discharging  of  Leyden  jars,  285 
Charging  the  Leyden  jar  by  cascade,  282 
Chemical  decomposition  by  electricity,  322 — 

327.  345.  35  < . 

Classification  of  bodies  into  electrics  and 
non-electrics,  236 

Comparative  specific  inductive  power  of  sub¬ 
stances,  312 
Conduction,  310 

Conductivity  of  non-electrics,  236 
Coulomb's  experiments,  259,  260,  261 
Coulomb’s  laws  of  attraction  and  repulsion, 
256—259.  3>3 
Crookes,  Mr.,  321 
Cruikshank's  experiments  on  the  voltaic  pile, 

343.  344,  345  ... 

Cruikshank  s  improvements  on  the  voltaic 
pile.  332.  333 
Cuneus,  277 

Cuthbertson’s  balance  electrometer,  292,  293 
Cylinder  electrical  machine,  250 
Cylindrical  glass  Coulomb  balance  or  electro¬ 
meter,  258,  310 

Daniell,  Professor,  310,  332,  334,  345,  356 
Daniell's  battery.  334,  340 
Daniell’s  diagrams  ;  surfaces  of  an  insulated 
and  non-insiilated  plate  of  glass,  268 
Davy's,  Sir  Humphrey,  experiment  in  the 
protection  of  copper  sheathing,  330 
Decomposition  of  water  by  electricity,  353 
Dei  man,  325 

De  la  Rive,  241,  258,  271,  289 

De  la  Rue  and  Muller’s  battery,  336,  337 

De  Luc,  246,  331 

De  Wilde,  Mr.  Sylvan,  368 

Dielectric,  269 

Difference  between  conductors  and  non-con¬ 
ductors  of  electricity,  265,  266 
Discharges  by  conduction,  by  disruption,  and 
by  convection,  313 

Distance,  influence  of,  in  attraction  and  re¬ 
pulsion,  255,  256 
Donne,  318 
Dry  pile,  the,  246 
Du  Fay,  241 

Dynamical  electrical  phenomena  obtained 
from  the  voltaic  battery,  341 
Dynamical  electricity,  315—347 
Dynamical  state  of  electricity,  241 


F.bner,  Baron,  372 

F.lectrical  accumulation,  laws  of,  309 — 314 
Electrical  attraction  and  repulsion  governed 
by  certain  laws,  255—  263 
Electrical  condenser,  the,  270 
Electrical  dance  of  puppets,  289 
Electrical  discharges,  313 
F.lectrical  dischargers,  291 — 294 
Electrical  excitation,  236,  240,  319 
Electrical  induction,  264 — 273,  310 
Electrical  machines,  248 — 255 


E  LECTRICIT Y  —continued. 

Electrical  probe  and  forceps,  368 
Electric  bell,  the,  289 
Electric  bomb,  the,  295 
Electricity  by  friction,  235,  240,  248 
Electricity  derived  from  chemical  action,  245 
Electricity  derived  from  evaporation,  245, 
248,  309 

Electricity  eliminated  by  combustion,  245 
Electricity  in  the  clouds,  245 
Electricity  obtained  from  glass  and  from 
sealing-wax,  240 
Electricity,  theories  of,  241,  242 
Electric  lamp,  the,  374 — 378 
Electric  light,  the,  in  vacuo,  367 
Electric  tension,  241 
Electric  torpedo,  the,  371 
Electric  well,  the,  262 
Electrode,  the,  346 
Electrography,  345 
Electrolytes,  347 
Electrometers,  257,  291 
Electro- motive  force,  359,  364 
Electrophorus,  the,  275 
Electroscope,  the,  236—240,  248,  255 
Electrotype,  345 

Elliott's  apparatus  to  show  the  time  occupied 
in  the  transmission  of  an  electric  current 
by  reflection,  298 
Ether,  242 

Experiments  in  oxidation,  320 
Experiments  showing  the  distribution  of 
electricity  on  the  surface  of  insulated  con¬ 
ductors,  260 

Experiments  with  cylindrical  conductor,  264 
Experiments  with  the  electroscope,  237—240, 
242 — 248  ;  conclusions  therefrom,  240 
Experiments  with  the  hydro-electric  machine, 
305 — 309 

Experiments  with  the  Leyden  jar,  battery, 
and  the  electrical  machine,  285 — 290 
Experiments  with  the  Leyden  jar  and  the 
electrical  dischargers,  294—302 
Experiment  with  the  heated  tourmaline,  243 


Faraday',  245,  260,  265,  267.  269.  310,  321,  331 
Faraday  s  apparatus  for  determining  the  spe¬ 
cific  inductive  power  of  various  substances, 

Faraday’s  experiment  with  the  conical  muslin 
bag,  260  . 

Faraday's  illustration  of  the  carrying  dis¬ 
charge,”  313  _ 

Faraday’s  induction  theory,  267,  310 

Faraday’s  researches,  345 — 354 

Fechner,  360,  364 

Fire  house,  the,  302 

Force  of  torsion,  258 

Force  of  unity,  256 

Foster,  Professor  G.  C.,  273 

Franklin,  241,  242,  280 

Franklin’s  experiment  with  Leyden  jar,  280, 
283,  312  .  .  , 

Frictional  electricity  without  friction  by 
Holtz  s  electrical  machine,  254 


Galcazzi,  Professor,  316 
Galvani.  242,  315,  316,  317 


726 


INDEX. 


ELECTRICITY  — continued. 


ELECTBICIT  Y — continued. 


Galvanic  battery,  the,  331 
Galvanic  electricity,  315 — 345 
Galvani’s  experiment  on  the  nerves  and  mus¬ 
cles  of  a  dead  frog,  315 
Galvanometer  multiplier,  the,  320 
Galvanometer  needle,  the,  319 
Galvano-plastic,  345 
Gassiot,  j.  P.,  240 

Glass  cells  for  chemical  decomposition,  355 
Gold-leaf  condenser,  the,  271 
Goodman,  Mr.,  252 

Gramme’s  magneto-electric  machine,  375 
Grove,  Professor,  367 
Grove  s  battery,  336,  340 
Grove’s  experiment  with  the  voltameter,  355 
Grove’s  gas  battery,  355 


Hare’s,  Dr.  Robert,  electroscope,  240 
Harris,  Sir  W.  S.,  251,  258,  269,  292,  3t2,  314 
Harris’s  balance  electrometer,  258 
Harris's  experiment,  showing  that  attraction 
is  preceded  by  induction,  269 
Harris’s  thunder-cloud  needle,  3or 
Harris’s  unit  jar  and  balance,  3t2 
Hawkesbee,  250 
Henley's  electrometer,  285 
Henley’s  discharger  and  press,  294 
Holmes,  Nathaniel  J.,  37t 
Holtz’s  electrical  machine,  254,  264,  276 
Hydro-electric  machine,  the,  245,  303 


Igenhouz’s,  Dr.,  electric  machine,  250 
Induced  electricity,  264,  269,  3ro 
Inducteous  body,  the,  269,  3ro 
Induction,  240,  24s,  264 — 273,  3to 
Inductric  body,  the,  269 
Influence  of  distance  in  attraction  and  repul¬ 
sion,  255 

Insulation  of  non-electrics,  236,  268,  3ro 
Ions,  347,  350 


Jacobi’s  torpedoes,  372 


Lane’s  discharger,  291 

Lane’s  electrometer,  Harris's  improvements 
in,  29  r 

Lateral  discharge,  3r4 
Lenz,  M.,  360 
Leyden  battery,  the,  284 
Leyden  jar,  the,  277—285 
Lichtenberg  figures,  289 
Lightning  conductors,  301 
Lockey,  Rev.  F  ,  284 
Longmore,  Professor,  37  r 


Maas,  366 

Magneto-exploder,  Wheatstone’s,  372 
Magnus,  367 

Matteucci,  Professor,  3Z6,  329 
Maury,  Commander,  372 
Measurers  of  volta-electricity,  348,  354 
Measuring  resistances  of  wires,  363 
Methods  of  obtaining  constants  of  reophoric 
circuit,  360—363 


Miller’s,  Dr.,  illustration  of  the  lateral  dis¬ 
charge,  314 
Muller,  Hugo,  336 
Mullins’s  sustaining  battery,  340 
Muschenbroeck,  277,  278 


Naime,  Dr.,  250 
Neeff,  366 

Negative  electricity,  240,  347,  366 
Nicholson  and  Carlisle’s  experiments  on  the 
pile,  342 
Noad,  Dr.,  303 
Nollet,  Abbe,  250 


Ohm’s  law,  356 — 359 

Organic  electricity,  Aldini’s  experiments  in, 
287 


Pablochkoff,  Paul,  375 
Paets  van  Troostwyk,  325 
Pearson,  Dr.,  325 
Peclet,  M.,  245,  273 
Peltier,  M.,  245 

Perpetual  chime  with  De  Luc’s  columns,  247 
Physiological  effects  of  electricity,  326 
Pile,  the  voltaic,  332,  342 
Plate  electrical  machine  at  the  Polytechnic, 

250 

Polarity,  265,  309,  365 
Polytechnic  torpedo,  the,  373 
Priestley,  Dr.,  250 
Pouillet,  M.,  245,  360 


Quiescent  electricity,  24r,  248 


Repulsion,  237 — 255 
Resinous  electricity,  238 
Rheometers,  360 
Rheomotive  element,  360 
Rheomotive  series,  360 
Rheophore,  360 
Rheoscope,  360 

Rheostat  of  Wheatstone,  the,  359 — 365 
Rheotome,  360 
Rheotrope,  360 


Sabine,  Robert,  356 
Serrin’s  electric  lamp,  375 — 378 
“  Shooting  star  ’  experiment,  the,  296 
Singer  s  directions  for  constructing  the  dry 
pile,  246,  247 

Smee’s,  Alfred,  battery,  339,  340 
Smythe,  Professor  Piazzi,  372 
Specific  induction,  3ti,  3t2 
Spontaneous  discharge,  279 
Static  state  of  electricity,  24r 
St.  Paul’s  illuminated  by  the  electric  light, 
378 

Sturgeon,  Mr.,  2t9,  339 
Sturgeon’s  battery,  339,  340 
Sultzer,  242,  318,  3Z9 
Swammerdam,  3r6 
Symmer,  241,  242,  243 


INDEX. 


727 


ELECTRICIT  Y -continued.  ELECTRICIT  Y —continued. 


Table  of  Ions,  350,  351 
Telegraphic  alphabets,  446 
Tension,  electric,  241 
Thales,  235,  236 
Theories  of  electricity,  241,  242 
Theory  of  whitening  common  pins,  345 
Thompson’s,  Sir  YV.,  reflecting  galvanometer 
needle,  319 

Thunder-cloud  needle,  Harris’s,  301 
Time-gun  at  Newcastle,  372 
Torpedo,  the  electric,  371 
Torsion  electrometer,  257 
Tyndall,  Dr.,  242,  367 


Unit  jar  and  balance,  Harris’s,  312,  313 
Unity,  256 


Van  Breda,  366 
Van  Troostwyk,  Paets,  325 
Velocity  of  electricity,  296 — 299,  356 
Vitreous  electricity,  238 — 245,  309 
Voltaic  battery,  the,  341 
Voltaic  circuit,  327 


Voltaic  electricity,  315—345 
Voltaic  pile.  Cruikshank’s  experiments  on 
the,  343,  344 

Voltaic  pile,  the,  332,  342 
Voltameters,  348—350,  354,  355 
Volta’s  “ couronne  de  lasses,"  333 
Volta’s  electrophorus,  277 
Volta’s  experiments,  272,  273 
Vulcanite  plate  electrical  machines,  252 


Walker,  Mr.  Charles  V.,  271,  303,  314 
YVatson,  Dr,  250 

Watson’s,  Dr.,  electrical  machine,  248 
Wheatstone,  Sir  Charles,  297,  309,  359,  372 
Wheatstone’s  apparatus  for  measuring  tl'.e 
velocity  of  electricity,  297,  298 
YVheatstone’s  magneto-exploder,  372 
Wheatstone’s  rheostat,  359 
Wilkinson,  Dr.,  318 
Wilson,  Dr.,  250 

YY'inter’s  electrical  machine,  252,  253 
YVollaston,  Dr.,  322,  326,  333 
Wollaston’s  improvements  upon  Cruikshank’s 
arrangements  of  the  calorimeter,  333,  334 
Wray,  Mr.  Cecil,  321 


MAGNETISM. 

Accumulation  of  power  shown  in  the  static 
electric  machine,  412 

“Acoustic  Figures  of  Vibrating  Surfaces,”  427 
Adamant,  379 

Adie’s,  Mr.,  magnetographs,  385 
Alphabetical-dial  telegraph,  428 — 432 
Ampere,  M.,  400 

Ampere’s  hypothesis  of  magnetism,  403 
Apps’s  apparatus  with  Geissler’s  tubes,  417 
Apps’s  dia-magnetic  apparatus,  394 
.Apps’s  electro-magnetic  engine,  400,  407 
Arago,  M.,  393,  427 
Atlantic  telegraph  cable,  454 — 462 
Augmentation  of  the  power  of  the  electro¬ 
magnet  by  currents  produced  by  itself,  409 
—412,  427 

Automatic  printing  telegraphic  system,  453 
Axial  line,  the,  395 


Bancalari,  Father,  398 
Barlow,  Mr.,  388 
Bar  magnets,  380 
Beanes,  Mr.  Kdward.  418 
Bechey,  Admiral,  388 
Becker,  Mr.,  455 
Belcher,  Sir  Edward.  388 
Bell,  Professor,  463,  468 
Bentley,  Mr.,  415 
Botto,  Professor,  406 
Brett,  M.,  426 
Brewster,  Sir  David,  42 


MAGNETIS  ML— continued. 

Browning’s  magneto-electro  machine,  414 
Chladni,  427 

Chronoscope,  Wheatstone’s,  449 
Clarke,  E.  M.,  409 
Clark,  Mr.  Latimer,  454 
Classification  and  nomenclature  of  magnetic 
phenomena,  396,  397 
Compass,  the,  379,  382,  387 
Compound  horse-shoe  magazine  or  battery, 
380 

Conservation  of  force,  399,  470 
Cooke,  429 
Crampton,  426 
Crystallization  of  iron,  391 
Current  of  electricity  affecting  the  magnetic 
needle,  401 

Curved  magnetic  needle,  the,  388 


Dal  Negro,  406 
Daniell’s  battery,  406 

Dates  of  Wheatstone’s  telegraphic  inventions, 
426 

Davenport,  Mr.  Thomas,  406 
Davidson,  Mr.,  406 
Declinatjon  magnetograph,  384 
Declination  of  the  needle,  382 
De  la  Rive,  404,  426 

Deviation  of  the  compasses  in  iron  ships,  387 
Dextrorsal  helix,  402 
Dia-magnetic  repulsion,  397 
Dia-magnetism,  394 — 399 


723 


INDEX. 


MAGNETISM  —  continued. 

Dia-magnetism  of  gases,  398 
Differential  resistance  measurer,  Wheat¬ 
stone’s,  456 

Dipping-needle,  the,  or  inclination  compass, 

381,  388  _  . 

Diurnal  variations  of  the  magnetic  needle, 

382,  387  _ 

Dynamo-magnetic  machine,  the,  413 


Edison’s  electric  pen,  407 
Electricity,  419 
Electro-dynamics,  400 
Electro-magnet,  the,  394,  401,  409 
Electro-magnet  excited  by  a  rheometer,  410 
Electro-magnetic  engines,  400,  406,  407 
Electro-magnetic  locomotive,  the,  406 
Electro-magnetic  power,  402 
Electro-magnetism,  400 — 407 
Elliott’s  contrary  rotation  apparatus,  405 
Equatorial  position,  the,  395 
Experiments  in  electro-magnetism,  402 — 405 
Experiments  with  the  dia-magnetic  appara¬ 
tus,  395—399 


Faraday,  Professor,  392,  394,  396 — 399,  405 
—409,  427,  455 

Faraday’s  lecture  on  the  Conservation  of 
Force,  470 — 472 

Fast-speed  automatic  telegraphs,  426,  428, 
437 

Faulkner,  Mr.,  403 
Fishbourne,  Captain,  388 


Gassiot,  M.,  417 

Gassiot’s  cascade,  416 

Geissler’s  tubes,  417,  418 

Generation  of  ozone  by  the  induction  coil, 

417 

Gilbert,  Dr.  William,  384 
Gravitation,  471 
Gray,  Elisha  P.,  463,  468 
Grove's  battery,  406 


Hart,  Mr. ,  406 

Hearder,  Mr.,  415 

Heat  and  magnetism,  391,  398,  399 

Helices,  dextrorsal  and  sinistrorsal,  402 

Henry,  Dr.,  409 

Hjorth's  electro-magnetic  engine,  406 
Holmes,  Mr.,  409 
Holtz,  412 

Hopkins,  Mr.  Evan,  386,  387,  388 

Hunt,  Mr.  Robert,  402 

Hypothesis  of  magnetism.  Ampere’s,  404 

Improvements  in  electric  telegraph  apparatus, 

440—445 

Inclination  or  dip  of  the  needle,  382,  387 
Induced  currents,  408,  409 
Induced  magnetism,  382 
Induction,  382 

Induction  by  current  electricity,  408,  409 
Induction  coils,  415 

Inductive  power  of  magnetic  force,  382 


MAGNETIS  M  -  continued. 

Inductorium,  the,  41 1 

Instructions  for  keeping  the  telegraph  instru¬ 
ments  in  order,  433 

Instructions  for  working  the  telegraph,  432 


Jacobi,  Professor,  406 
Joule,  406 


King,  Mr.  J.  L.,  419 
Knoblauch,  397 
Konig,  427 


Ladd’s  coil,  413 

Ladd’s  electro-magnetic  machine,  412 
Ladd’s  ozone-tube,  417 
Lapis  Heracleus,  379 
Lapis  nauticus,  379 
Le  Sage,  463 
Line-printer,  the,  447 
Line-printing  transmitter,  447 
Loadstone,  379 

Locomotive,  the  electro-magnetic, 


Magnetic  field,  the,  395 
Magnetic  meridian,  382,  387 
Magnetic  needle,  the,  381,  388 
Magnetic  observatory  at  Stony  hurst,  385 
Magnetic  polarity,  383,  396 
Magnetic  poles,  382,  387 
Magnetic  stone,  379 
Magnetic  storm,  385 
Magnetization,  405 
Magnetized  steel,  380 
Magneto-electric  induction,  408,  409 
Magneto-electricity,  408 — 418 
Magneto-electric  machines,  409,  412 
Magnetographs,  384 
Magnets,  379,  394,  403 
Maguire,  Captain,  388 
Mammoth  induction  coil,  the,  418 
Marcus’s  thermo-electric  battery,  419 
Marine  azimuth  compass,  382 
Mariner’s  compass,  the,  379 
Matteucci,  Signor,  399 
Melloni’s  thermo-electric  pile,  420 
Moser,  391 
Mossotti,  471 


Natural  directive  power  of  magnetism,  384 
Neckham,  Alexander,  379 
Newton,  472 

Nicholson,  Sir  Frederick,  387 
Nitrogen,  397 
Noad,  Dr.,  415,  417 
Nollet’s  magneto-electric  machine,  409 
North  magnetic  pole,  382 


(Ersted,  400,  404 
Ohm’s  law,  427 

Oxygen,  magnetic  property  of,  398 
Ozone-tube,  Ladd's,  417 


INDEX, 


MAGNETIS  M—  continued. 

Page’s,  Professor,  electro-magnetic  engine, 
406 

Paget,  Mr.,  389 
Para-magnetism,  394,  397 
Parry,  Captain,  382 
Perry,  Rev.  S.  G.,  384 
Pixii,  409 

Plucker’s  experiments,  416,  417 

Plucker’s  tube,  416 

Polar  clock,  the,  43- 

Pouillet's  thermo-electric  apparatus,  420 

Preece,  W.  H.,  467 

Prince  Consort,  the,  402 

Prismatic  analysis  of  electric  light,  427 


Quetelet,  427 


Reich,  397 
Riess,  391,  467 
Ritchie's  spirals,  405 
Romershausen,  403 
Ross,  Captain  James,  382 
Rotating  mirror,  the,  427 
Rotation  experiments,  392,  398,  406 
Ruhmkorff’s  induction  coil,  415 


Sabine,  General,  382 
Sail-stone,  the,  380  § 

Saxby's  method  of  testing  iron  by  magnetic 
power,  388 — 391 
Saxton,  409 

Scoresby's  magnets,  381,  406 
Seebeck's  thermo-electric  apparatus,  419 
Selwyn,  Captain,  388 

Shepherd,  the,  discovering  the  magnetic  stone 
on  Mount  Ida,  379 
Siderites,  379 
Siemens,  C.  W.,  410,  412 
Siemens’s  armature,  410,  412 
Single  and  double  needle  telegraph,  429 
Sinistrorsal  helix,  402 
Somerville,  Mrs.,  391 
South  magnetic  pole,  382 
Static  electric  machines,  412 
Stereoscope,  the,  417 


Talbot,  406 
Taylor,  Sir.,  406 

Telegraph  cable,  Atlantic,  454 — 462 
Telegraphic  alphabets,  446 


729 


MAGNETIS  M — cot  1  tin  tied. 

Telegraphic  perforation,  442 
Telegraphic  recorders,  442,  445 
Telegraphic  translators,  439 
Telegraphic  transmitters,  438,  447 
Telegraphs,  Wheatstone’s,  425—453 
Telephone,  the,  463 
Terrestrial  magnetism,  384,  386 
Terrestrial  meridian,  384,  386 
Terrestrial  power  of  magnetism,  382,  387 
Thermo-electric  batteries,  419,  420,  421 
Thermo-electricity,  4t9,  420,  421 
Thompson’s  reflecting  galvanometer  needle, 
455 

Transmission  of  sound  through  solid  con¬ 
ductors,  427 
Tyndall,  Dr.,  397 
Type-printing  telegraph,  426,  429 


Unit  of  the  British  Association,  454 


Van  der  Voort’s  thermo-electric  battery,  421 
Van  Malderen’s  magneto-electric  machine, 
4°9 

Volta-electric  induction,  408,  409 


Watkins,  Mr.  Francis,  420 
Weber,  397 
Welch,  Air.,  385 

Wheatstone,  Sir  Charles,  391,  406,  409,  412, 
425—428,  453 

Wheatstone’s  bell  in  box  for  military  service, 
435  , 

W  heatstone’s  bridge,  427,  455 
Wheatstone's  chronoscope,  449 
Wheatstone’s  communicator,  429 
Wheatstone’s  dials  for  iron-clad-.,  436 
Wheatstone’s  experiments  with  the  electro¬ 
magnet,  409 

Wheatstone’s  exploder,  409 
Wheatstone’s  first  alphabet-dial  telegraph, 
429 

Wheatstone’s  last  telegraphic  apparatus,  446 
Wheatstone’s  method  of  delecting  minute 
quantities  of  magnetic  force  in  metals,  391 
Wheatstone’s  recording  thermometer,  451 
Wheatstone’s  recording  instrument  for  news¬ 
paper  offices,  436 

Wheatstone’s  telegraphs,  425 — 453 

Wilde,  Mr.,  410,  412 

Wray’s  patent  thermo-electric  pile,  421 


PNEUMATICS. 

Air,  473,  493,  5°7 

Air-pump,  the,  474 — 403,  508 — 510 

Anemograms,  496 

Aristotle,  474 


PNEUMATIC  S —continued. 

Bacon,  Roger,  487 
Barker,  Mr.,  510,  511 
Barograms,  496 
Barometer,  the,  493 — 500 


73° 


INDEX. 


PNEUMATIC  S — continued. 

Barometer  in  the  vacuum  of  an  air-pump,  493 

Barometrical  observations,  498,  499 

Blower,  the,  473 

Boerhaave,  473 

Booth,  Mr.,  511 

Borelli,  485,  487 

Boyle,  507 

Braithwaite,  Messrs.,  487 
Breary,  Mr.,  502 

Bushnell's  tortoise-shell  contrivance  for  the 
diving-bell,  485 


Cabirol,  M.,  488 
Castelli,  Benedetto,  492 
Clark,  Mr.  Latimer,  513 
Clegg,  Samuel,  513 

Complete  pump  for  philosophical  purposes, 
476  _ 

Condensing  pump,  the,  481 
Construction  and  operation  of  the  common 
water-pump,  502 

Copy  of  a  barogram  from  Stonyhurst,  497 
Copy  of  a  thermogram  from  Stonyhurst,  498 
Crookes,  481 
Ctesibius,  502 


Daedalus,  501 

Davis's  barometer  and  weather  guide,  495 
Debrell,  487 
Despretz,  507 
Diving-bell,  the,  484 
Diving-dresses,  485 
Diving-engine,  Rowe’s,  483 
Double-acting  air-pump,  478 
Double-cylinder  air-pump,  480 


Elasticity  of  air,  507 — 510 
Elasticity  of  gases,  508 
Ernoux,  M.,  486,  488 
Ernoux’s  diving  apparatus,  489 
Experiments  with  the  air-pump,  491,  492 


Fitzroy,  Admiral,  495 
Fitzroy’s  storm  drum,  495 
Forcing  pump,  502,  504 
Fortin,  494 
Flying  machines,  502 


Galileo,  492,  502 
Geissler  tube,  the,  480 
Glaisher,  Mr.,  502 


Halley’s  diving-bell,  484 

Halley’s  truncated  wooden  cone,  483 

Hamilton,  Mr.  David,  51 1 

Heinke’s  diving  helmet  and  dress,  485 — 488 

Hemispheres,  the  Magdeburg,  491 

Herapath,  Dr.,  496 

Hippocrates,  473 


Illustrations  of  the  action  of  the  air-pump, 
476 — 480 


PNEUMATIC  S — continued. 

Imison,  492 
Impenetrability,  474 


Law  of  Marriotte,  the,  506 
Lewis,  513 

Lifting  pump,  502,  305 


Magdeburg  hemispheres,  the,  491 
Marriotte,  506,  507 

Martin’s  contrivance  for  the  diving-bell,  483 
Medhurst,  513 

Mercury  machine,  Alvergniat’s,  481 
Miller,  Dr.,  507 

Miniature  fountain — water  forced  out  by  the 
elasticity  of  the  air,  509 
Miniature  windmill,  509,  310 
Mouse  under  water,  the,  484 
Murdoch,  Mr.,  513 


Ostler’s  self-registering  anemometer,  500 
Owen,  Rev.  J.  B.,  484 


Papin,  Dr.,  513 

Perry,  Rev.  S.  G.,  487 

Phipps,  484,  487 

Piezometer,  509,  510 

Pinkus,  Mr.,  513 

Plunger  force-pump,  505 

Pneumatic  Despatch  Company’s  tube,  473, 

513  •  , 

Pneumatic  lever,  the,  510 

Pneumatic  lever  applied  to  the  organ,  510 
Pneumatic  tubes,  513 

Pneumatic  tube  at  Euston  Square  Station, 
5T4 

Pressure  of  air,  491,  505 


Rammel,  Mr.,  5r4 
Rarefaction  of  air,  476 
Regnault,  507,  508 
Rowe’s  diving-engine,  485 


Samuda,  Jacob,  5t3 

Self-registering  barometer  at  Stonyhurst,  496 
Siebe,  M.,  488 

Siebe’s  diving  apparatus,  489 
Siemens’s  air-pump,  474 
Smeaton,  487 
Smeaton’s  diving-bell,  484 
Specific  gravity  of  air,  493 
Sprengel’s  air-pump,  481 
Square  bottle  burst  by  the  elasticity  of  the 
air,  508 

Standard  aneroid  barometer,  500 
Standard  barometer  by  Negretti  and  Zambra, 
494 

St.  Martins’  flying  machine,  501 
Submarine  lamp,  the,  486 
Sucking  pump,  the,  302 
Suction,  492,  507 
Syphon,  the,  506 


INDEX. 


73i 


pneumatic  s— continued. 


PNEUMATIC  S — continued. 


Thermograms,  496 
Torricelli,  Evangelista,  492 
Torricellian  vacuum,  492,  493 
Triewald,  487 

Tortoise-shell  contrivance  for  the  diving-bell, 
485 

Tylers,  Messrs.,  apparatus,  489 


Use  of  air-pumps,  481 


Vacuum,  476,  492 

Vallance,  Mr.,  513 

Various  forms  of  water-pumps,  504 


Water-pumps,  502 

Wheel  barometer,  the,  492,  500 

Wilkins,  Bishop,  487 


ACOUSTICS. 

Acoustics  of  public  buildings,  the,  531 

Airy,  Mr.  Hubert,  562 

Albertus  Magnus,  516,  558,  568 

Aldous,  Mr.  Lewis,  519 

Analogy  between  ligh  and  sound,  558,  559 

Analyzing  a  mixture  of  sounds,  525 

Anthropoglossos,  the,  558,  568 

Aquinas,  Thomas,  568 

Arago,  M.,  571 

Aristotle,  516 

Arrangement  of  reeds  and  mirrors  in  Pichler’s 
harmony  and  discord  apparatus,  560 


Bacon,  Lord,  570 
Barbereau,  M.,  520 
Barrett,  Mr.,  534,  535,  541 
Bates,  Mr.  H.  W.,  550 
Becker,  Mr.,  543 

Bell  shaken  or  rung  in  a  vacuum,  533 
Bibot,  566 

Biot,  M.,  567,  568,  570 
Blackburn,  Professor,  562 
Bouvard,  570 
Brande,  546 
Brugnatelli,  541,  545 


“  Canard,”  the,  519 
Chevallier,  Charles,  517 
Chladni,  517,  560,  566,  570 
Chladni’s  sand  figures,  517,  538,  554 
“Clacque-bois,”  554 

Colladon  and  Sturm’s  experiments  in  the 
transmission  of  sounds,  569 
Considerations  on  sound,  527 — 532 


Davy,  Sir  Humphrey,  545 
De  la  Rive,  541,  545 
Delezenne,  M.,  527 
Despretz,  520 

Differential  sonometer,  Marloye's,  552 
Duchemin,  M.,  524 
Duhamel,  M.,  527 

Dulong's  table  of  the  velocity  of  sound,  569 


Ear,  the,  518—523 


ACOUSTIC  S — continued. 

Echoes,  558 

Education  of  the  ear,  517,  523 — 547 
Embouchure,  the,  557 
Ether,  558 

Experiments  in  resonance  with  the  tuning- 
fork,  547  .... 

Experiments  on  strings  in  vibration,  527 — 530 
Experiments  in  the  production  of  sound,  541 
Experiments  showing  the  reflection  of  sound, 
558,  559 

Experiments  with  Savart’s  apparatus,  547 


Faber,  Herr,  558 
Faraday,  Professor,  541,  543,  545 
Flames  sensitive  to  sound,  534 
Franklin,  Dr.,  569 

Froment’s  apparatus  for  converting  noise  into 
musical  sounds,  540 


Galileo,  516 

Galton,  Professor,  539 

Gamut  or  musical  scale,  the,  538 

Gases  sensitive  to  sound,  535 

Gas-flame  organ,  543,  544 

Gay-Lussac,  570 

Guido  of  Arezzo,  538 


Hassenfratz,  Rafn,  570 
Harmonic  notes,  528,  538 
Harmony  and  discord  of  sounds,  560 
Helmholtz,  556 
Herholt,  570 

Herschel’s,  Sir  John,  experiments  giving 
two  sounds  resulting  in  silence,  560 
Higgins,  Dr.,  541,  545 
Hooke,  Dr.,  570 

Hydrogen  gas  and  sound,  533,  545 


Importance  of  educating  the  ear  to  hear  r.nd 
distinguish  sounds,  518,  521,  531 
Intensity  of  sound,  524 
Intervals  of  sound,  566,  571 
Invisible  girl,  the,  568 


732 


INDEX. 


ACOUSTIC  S —continued. 

Ladd,  Mr.,  539,  540 
Laplace,  566 
'  Latour,  Cagniard,  536 
Laws  of  the  propagation  of  sound,  567 
Lecomte,  Professor,  535 
Le  Cour,  565 
Lissajous,  M.,  560 

Longitudinal  vibrations  of  columns  of  air,  553 
Longitudinal  vibrations  of  strings  and  rods, 
551 

Lowest  and  highest  sound  the  ear  can  appre¬ 
ciate,  539 

Marloye,  M.,  517,  539,  552.  554.  555,  557 
Marloye’s  differential  sonometer,  552 
Marloye’s  introduction  to  Chevalliers  cata¬ 
logue,  517  . 

Marloye’s  longitudinal  musical  instrument, 
553 

Martin,  570 

Model  of  the  mechanism  called  the  Piping 
Bullfinch,  575 
Moigno,  Ahbe,  554 
Monochord,  the,  528,  538,  331 
Morton’s,  Professor,  experiments,  547 
Music,  517 

Musical  flames,  541,  544 
Musical  pitch,  the,  549,  560 


Newton,  570 

Nodal  or  fixed  points,  538,  543,  551,  557 
Noises  converted  into  musical  sounds,  536, 
54° 


ACOUSTIC  S — continued. 

Sauveur’s  explanations  of  the  “  beats  ”  of  the 
organ,  559 

Savart,  517,  527,  330,  539  _ 

Savart's  apparatus  for  showing  resonance,  546, 
554 

Scheibler,  360 
Seguier,  M.,  521 
Sensitive  flames,  533,  536 
Shalckenbach,  Herr,  543 
Sonometer,  the,  524,  527,  529,  552 
Sound,  517,  525—527,  53i,. 533 
Sounds  produced  by  flame  in  tubes,  Faraday’s 
lecture  on,  545 
Speaking  heads,  558,  568 
Speaking-trumpet,  the,  567 
Speaking-tubes,  56S 
Spicer,  Mr.  Robert,  548 
Stethoscope,  the,  567 
Study  of  musical  intervals,  523 
Sturm,  569 

Sympathetic  resonance  of  tuning-forks,  548 
Syren,  the,  536—540 


Talking  head  of  Albertus  Magnus,  516 
“Tanana,”  the,  550 
Telephonic  concert,  the,  573 
Tisley’s  compound  pendulum,  562 
Transmission  and  reflection  of  sound,  532 
Transmission  of  sounds  through  gaseous, 
liquid,  and  solid  media,  566 — 575 
Transversal  vibrations  in  strings,  551 
Transverse  vibrations  of  blades  and  rods,  554 
Tuning-fork  as  a  telegraphic  instrument,  565 
Tuning-forks,  571 
Tympanum  of  the  ear,  519 
Tyndall,  Dr.,  517,  535,  556 


Organ-pipe  and  flame,  542 

Organ-pipes  fitted  on  table,  and  bellows,  556 


Undulatory  theory  of  light,  517,  552 


Perotti,  M.,  570 

Piano  constructed  of  pebbles,  534 
Pichler,  Mr.,  536,  560 

Pichler’s  apparatus  for  showing  the  harmony 
and  discord  of  sounds,  560 
Pichler's  apparatus  for  showing  the  nodal 
points  in  organ-tubes,  557 
Pictet,  541,  545 
Piping  Bullfinch,  the,  575 
Polarization  of  light,  559 
Polarization  of  sound,  559 
Projects  of  study  concerning  the  acoustics  of 
public  buildings,  532 
Pythagoras,  516 


Reed,  the,  558 
Reflection  of  sound,  558,  559 
Refraction  of  sound,  559 
Resonance,  541,  546,  57T 
Resonance  of  sounding-boards,  571 
Resonant  insect,  a,  550 
Rotation  of  lycopodium,  554 


Velocity  of  sound,  566 — 570,  573 
Ventral  segment,  the,  538,  551,  556 
Verification  of  the  law  of  diameters,  552 
Verification  of  the  law  of  tensions,  552 
Vibrating  plates,  554 
Vibrations  of  liquids  and  gases,  5t7,  534 
Vibrations  of  the  seven  notes  of  the  gamut, 
538 

Vibrations  of  the  tuned  string,  ssr,  552 
Vibratory  motions  of  strings,  529,  551 


Waves  of  sound,  534,  538,  558 
Wertheim,  569 

Wertheim's  table,  showing  the  transmission 
of  sound  through  solid  conductors,  569 
Wheatstone,  517,  569,  570,  573 
Wheatstone's  experiments  on  the  transmission 
of  sound,  570 — 573 
Wheatstone's  wave  apparatus,  534 
Willis,  Professor,  558 
Wollaston,  Dr.,  539 
Wunsch,  Professor,  570 


Saunderson,  Professor,  559 
Sauveur,  Joseph,  559,  560 


Young,  Dr.  Thomas,  517 


INDEX. 


733 


CHEMISTRY. 


CHEMISTR  Y  -continued. 


Abel,  Professor,  610 

“  Acids,”  590,  634 

Acids  of  phosphorus,  the,  660,  661 

Addams,  Mr.  Robert,  635 

Adhesion,  578,  583 

Agate  pestle  and  mortar,  698 

Agate,  varieties  of,  644 

Agricola,  669 

Air  the  standard  for  determining  the  specific 
gravity  of  gaseous  bodies,  579 
Aluminium,  sources  of ;  processes  for  obtain¬ 
ing  ;  properties  of;  oxide  of ;  salts  of ;  use 
in  commerce,  677,  678,  679 
Ammonio-magnesic  phosphate,  682 
Ammonia,  sources  of;  properties  of,  618,  619 
Ammonium,  properties  of;  uncertainty  as  to 
its  being  a  metal,  675 
Amorphous  boron,  639,  640 
Amorphous  phosphorus,  658,  659,  660 
Antimony,  sources  of  ;  physical  and  chemical 
properties  of :  oxides  of;  uses  in  commerce, 
667,  668 

Antimoniuretted  hydrogen,  668 
Antique  cameos,  645 

Apparatus  for  compressing  in  the  manufac¬ 
ture  of  gun  cotton,  613 
Apparatus  for  exhibiting  cohesion  figures,  583 
Apparatus  for  making  and  washing  oxygen 
gas,  596 

Apparatus  for  purifying  crude  sulphur,  650 
Aqua  fort  is,  609 
Archer,  Mr.  Scott,  624 

Arsenic,  sources  of ;  physical  and  chemical 
properties  of ;  oxides  of  ;  uses  of ;  testing 
operations  for  ;  trichloride,  663 — 667 
Arseniuretted  hydrogen,  667 
Artificial  graphite,  631  ;  do.  quartz,  646;  do. 

vellum,  used  in  making  gun  cotton,  614 
Atmospheric  air,  600 
“  Atom,”  592 

Atomic  weight,  592 ;  do  ,  table  of,  591 
“  Azot,"  600 


Bacteria,  601 
Balard,  627 

Barium,  properties  of :  oxides  of ;  salts  of,  677 
Beakers  in  which  to  prepare  solutions,  666 
Bell,  Jacob,  654 

Bell's  process  for  obtaining  aluminium,  679 
Berg  crystal,  643 
Berzelius.  646,  647,  697 

Bessemer’s  process  of  steel  manufacture,  688 
Bichloride  of  platinum,  705 
Binary  compounds,  589 
“  Binoxide,  589  ;  do.  of  oxygen,  598 
Bismuth,  sources  of ;  physical  and  chemical 
properties  of ;  oxides  of ;  uses  of ;  analogy 
to  nitrogen,  phosphorus,  &c.,  668—670 
Bismuth  glance,  669 
“  Bittern,"  the,  622,  627 
Black,  Dr.,  634  . 

Blowpipes  used  by  chemists,  &c.,  665 
Boiling-point  of  water,  he,  666 
Bone-black  or  animal  charcoal,  631 
Boron  ;  boracic  acid,  639,  640,  641 
Boussingault,  600 
Boyle,  654,  65 6 

Brandt,  Dr.,  638,  654,  663,  692 


Brewster,  Sir  David,  portrait  and  autograph 
of,  630 ;  do.  on  the  cavities  in  diamonds,  633 
Brodie’s  experiments  with  graphite,  631 
Bromine,  627  ;  bromous  chloride,  628 
Brook  crystal,  643 
Bunsen.  674,  680 
Burnett’s  disinfecting  fluid,  684 
Bussy,  M.,  680 

Cadmium,  oxide  of ;  salts  of,  684,  685 
Cscsium,  sources  of ;  compounds  of,  674,  675 
Calcium,  sources,  properties  and  oxide  of,  6^6 
Calomel,  586 
Calotype,  the,  623,  624 
Carbon  or  charcoal,  629,  631,  634 — 638 
Carbon  photograph,  the,  626 
Carbonic  acid  or  dioxide  ;  carbonic  acid  gas 
evolved  in  the  fermentation  of  beer;  do.  in 
pits  ;  carbonic  anhydride  ;  do.  oxide,  634 — 
638  ;  do.  bisulphide,  654 
Caron,  M.,  680 
Cavendish  bottle,  the,  607 
Cavities  in  gems,  645 
Centrifugal  drying  machines,  6rr 
Chalcedony,  the,  645 
Charcoal,  various  kinds  of,  631 
Chemical  action,  578 — 587 
Chemical  compounds  of  oxygen  and  nitiogen, 
608,  609 

Chemical  composition  of  water,  666 

Chemical  reaction,  592 

Chlorine,  586 ,  do.  gas,  620 

“  Chlorophanc,’  629 

Choke-damp  of  mines,  635 

Chromium,  sources  of:  oxides  of;  salts  ol ; 

uses  in  commerce,  693 
Classification  of  the  metals,  670 
Claus,  M.,  598,  705 
Coal-gas,  638 

Cobalt,  properties,  oxides,  and  salts  of.  692 
Cohesion,  S83 
Colloids,  585 

Comparison  between  white  and  led  phospho¬ 
rus,  658 

Copper,  properties,  oxides,  and  salts  of,  702 

Corrosive  sublimate,  586 

Cort,  Mr.,  688 

Coster,  Mr.,  633 

Courtois,  622 

Cronstedt,  693 

Crookes,  Mr.,  697 

Crystalloids,  5S5 

Cupellation  ;  cupel  moulds,  698 

Daguerre,  M.  ;  the  daguerreotype,  623 
Daniell,  579,  583 
Darker.  Messrs.,  596 
Daubeney,  Dr  ,  599 

Davy,  Sir  Humphrey,  576,  639,  67t,  676,  iSt 

De  Babo,  M.,  598 

Debray,  M.,  704 

Decomposition  of  water,  606 

Definite  proportions,  586 

Dephlogisticated  air,  594 

Deutoxide,  the,  589 

Deville,  M.,  639,  680,  704 

Deville’s  process  for  obtaining  aluminium,  680 
Dialysis,  583,  584 


734 


INDEX. 


CHEMISTB  Y— continued. 

Diamond,  the,  629,  632 

Dibasic  acids,  590 ;  dibasic  phosphorous  acid, 
661 

Diemen,  638 
Dihydric  sulphide,  653 
Discoverer  of  oxygen,  the,  593 
Distilling  apparatus,  605 
Dithionic  acid,  65r,  653 
Dragonite,  643 
Dufay,  655 
Duhamel,  655 
Dumas,  600 

Dutrochet's  endosmometer,  584 
Dyad,  the,  590 

Ebelmas,  M.,  678 
“  Eburneum  ”  photographs,  626 
Elements  which  are  not  metallic,  593 — 654 
Elkington's  Milton  Shield,  700 
Endosmosis,  514 
Equivalent  proportions,  587 
Ethylene,  638 
Eudiometer,  the,  607 
Exosmosis,  584 

Experiments  on  the  weights  of  air,  603 
Experiments  with  ammonia,  618  ;  with  car¬ 
bonic  acid  gas,  635  ;  with  Galibert’s  appa¬ 
ratus,  636  ;  with  gun  cotton,  616 ;  with 
oxygen  and  hydiogen,  607  ;  with  the  osmo¬ 
meter,  584;  with  solid  carbonic  dioxide,  635 

Faraday,  Michael,  portrait  and  autograph  of, 
576 

Feldspar,  671 
Ferrous  sulphide,  653 

Fire-clay  furnace  for  crucible  operations,  640 

Fire-damp,  638 

“  Fixed  air,”  634 

“  Flos  philosophorum,”684 

Fluorine,  628 

Fluor-spar,  629 

Fordos,  M.,  623 

Forge,  bellows,  and  iron  tray  apparatus,  640 
Fourcroy,  655 

Furnace  for  crucible  operations,  639 
Gahn,  655,  692 

Galibert's  respiratory  apparatus,  636 — 638 
Gas  burner  and  crucible,  641 
Gas  burners,  various,  595 
Gas  generator  and  other  apparatus,  597 
Gelis,  M.,  623 

Gems,  how  to  manufacture,  644 
Geoffroi,  655 
Gerhardt,  661 
German  silver,  693 
Gmelin,  670 

Godfrey  and  Cooke,  Messrs.,  654 

Gold,  sources  whence  derived  :  properties  of ; 

uses  in  commerce,  705 — 710 
Gore,  Mr.  George,  654 
Graham,  Mr.,  676 

Graham,  Professor,  584  ;  his  analysis  of  the 
composition  of  air,  604 
Graphite  ;  graphitic  acid,  631 
Graphitoid  boron,  639 
Gravitation,  578 


CHEMIST  B,  Y — continued. 

Gravity,  definition  of,  578 
Griffiths,  649,  683 

Guano,  why  it  is  used  as  a  manure,  618 
Gun  cotton,  609 — 6r8 


Hadow,  Mr.,  612 

Haidinger,  683 

Hall,  Messrs.,  609 

Halogens,  the,  620 — 629 

Hanckwitz,  Ambrose  Godfrey,  654 

Hard  porcelain  cups  and  crucibles,  664 

Hard  water,  605 

Hartshorn,  6t8 

Hauy  Naumaun  crystal,  643 

Hausmann  crystal,  643 

Heaton’s  process  for  the  manufacture  of  steel, 
688 — 69  r 

Heavy  carburetted  hydrogen,  638 
“  Heavy  spar,”  677 
Hellot,  655 
Herodotus,  687 
Herschel,  Sir  John,  624,  693 
Herschel’s  objections  to  the  alteration  of  che¬ 
mical  terms,  588 
Heterogeneous  adhesion,  583 
Flexad,  the,  590 

Highley’s  arrangement  for  making  and  wash¬ 
ing  oxygen  gas,  596 

Hofmann,  Dr.,  on  classification  and  nomen¬ 
clature  in  chemistry,  588 
Hope,  Dr.,  676 

How  jewellery  is  made  by  machinery,  706 
How,  Mr.,  594 
Humboldt,  Baron  von,  642 
Hunt,  Mr.,  687 

Hydric  chloride,  621  ;  do.  persulphide,  654 
Hydriodic  and  hydrobromic  acids,  627,  628 
Hydrochloric  acid,  621 
Hydro-fluoric  acid  or  hydric  fluoride,  629 
Hydrogen  ;  to  prepare  it ;  water  the  source 
of;  chemical  composition  of;  combinations, 
604 — 619 

Hydrogenium  a  metal,  676 
Hydrophane,  646 
Hydro-potassic  tartrate,  671 
Hydro-sulphuric  and  sulphurous  acids,  653 


“  Inflammable  air,”  607 
Influence  of  oxygen  on  health,  598 
Influence  of  the  sea  in  augmenting  the  amount 
of  ozone  in  the  air,  599 
Indium,  oxide  of ;  compounds  of,  694 
Iodine,  622,  627 
Iridium,  704 

Iron,  processes  of  smelting,  685 — 687  ;  and  of 
puddling,  688 

Iron,  sources  of,  685  ;  physical  and  chemical 
properties,  oxides,  and  salts  of,  691 
Iron  pyrites,  691 


James’s  powder,  668 
Johnston,  Professor,  659 


Kane,  Dr.,  650 
“  Kupfer  Nickel,"  693 


INDEX. 


735 


CHEMISTE  Y — continued. 

Kirchoff,  674 

Kirkaldy’sexperimentson  the  tensile  strength 
of  steel,  690 
Klaproth,  662,  693 
Koh-i-noor,  the,  632 

Lampblack  charcoal,  631 
Lapping  machine  for  polishing  the  bright 
parts  of  gold  ornaments,  708 
Larkin,  Mr.,  682 
Laughing  gas,  609 
I.aurenberg,  638 
Lavoisier,  593 

Laws  of  chemical  attraction,  586 
Lead,  properties  of;  oxides  and  salts  of ;  uses 
in  commerce,  696 

Lenk,  Baron  von,  610;  his  gun  cotton,  612 
Life  of  Michael  Faraday,  576 
Light  carburetted  hydrogen,  638 
Lime,  salts  of,  676 

Liquefaction  of  carbonic  anhydride,  63s 
Lithium,  sources,  properties,  and  compounds 
of,  675 
Louzet,  629 


Macquer,  M.,  503 
“  Magistery  of  bismuth,”  the,  669 
Magnesium,  sources  of;  process  of  obtain¬ 
ing  ;  oxides,  salts,  silicates,  and  phosphates 
of,  680 — 682 

Magnesium  balloons  at  Crystal  Palace,  682 
Magnesium  light,  the,  682 
Manganese,  sources,  oxides,  salts,  and  pro¬ 
perties  of,  692 

Manufacture  of  gems,  the,  644 
Marchand,  669 
Margraaf,  655 
Marsh  gas,  638 
Marsh's  test  for  arsenic,  666 
Mercurial  troughs,  608 
Mercu  ic  chloride,  586 
Mercurious  chloride,  586 
Mercury,  sources,  properties,  oxides,  and 
salts  of,  704 

Metallic  nature  of  arsenic,  663 
Metallic  salts  formed  from  phosphoric  acids, 
66 1 

Metals,  662 — 710 

Metals  of  the  alkalies  ;  of  the  alkaline  earths ; 

of  the  earths,  671 — 679 
Metaphosphoric  acid,  661 
Meteorites,  685 

Methods  of  preparing  oxygen  gas,  594 — 597 

Methyl  hydride,  638 

Mica,  671 

Michel,  649 

Miller,  Dr.,  648,  670 

Miller,  Professor,  603 

Miller's,  Professor,  analysis  of  the  steel  made 
by  Heaton’s  process,  688 
Milton  shield,  the,  700 
Mispickel,  663 

Modes  of  determining  the  specific  gravity  of 
solids,  liquids,  and  gases,  579 
Modes  of  decomposing  water,  606 
Modifications  of  adhesion,  583  ;  of  sulphur, 
651 


CHEMISTE  Y — continued. 

Moffat,  Dr.  R.  Carter,  on  the  process  of  oleo¬ 
graphy,  579—582 
Moh.  Professor,  642 
“  Molecule,”  592 
Monads,  the,  590,  620 
Monobasic  acids,  590 
Monobasic  hypophosphorous  acid,  661 
Morin,  General,  61 1 
“  Mother  liquor,”  622,  628 
Muffles  for  assaying  silver  and  gold,  698 
Multiple  proportions,  586 
Murray,  Mr.  Robert,  577 
Muschenbroek,  606 
Mushet,  687 

Muspratt,  Professor,  649,  659 


Native  sulphur,  649 
Naumaun  crystal,  683 
Negative  osmose,  584 
Newton,  Sir  Isaac,  578 

Nickel,  properties,  oxides,  salts,  and  com¬ 
pounds  of ;  use  in  commerce,  693 
Niobium, 694 
Nitre  or  saltpetre,  672 

Nitric  acid,  anhydride,  oxide,  tetroxide,  and 
trioxide,  609 — 61 1 

Nitrogen,  to  prepare  ;  properties  of,  600 
Nitrogen  and  hydrogen,  608 
Nomenclature,  chemical,  588 — 592 
Normandy’s,  Dr.,  burner,  666;  mixed  air  and 
gas  burner,  641 
“Nuggets,"  705 


Oil-films  in  water,  580 
Oil  of  vitriol,  652 
Olefiant  gas,  638 

Oleographs  of  tallow  and  lard,  580 
Oleography,  579 

Origin  of  the  terms  phosphorus,  ammonia, 
and  potash,  588 
Orpiment,  663 
Osmium,  705 

Osmometer,  the  ;  “  osmose,"  583 
Ovens  for  drying  precipitates,  669 
Oxidation,  597 

Oxides— of  aluminium,  679  ;  antimony,  668  ; 
arsenic,  663  ;  barium,  677  ;  bismuth,  669  ; 
boron,  640;  bromine,  628;  cadmium,  685; 
caesium,  675;  calcium,  676;  carbon,  634 ; 
chromium,  693 ;  cobalt,  692  ;  copper,  702  ; 
iodine,  627  ;  indium,  694  ;  iron,  691 ;  lead, 
696;  lithium,  704  ;  magnesium,  682;  man¬ 
ganese,  692;  mercury,  675;  nickel,  693; 
platinum,  705;  phosphorus,  660 ;  potassium, 
672 ;  rubidium,  651  ;  silicon,  642  ;  silver, 
699;  sodium,  674;  strontium,  676;  sulphur, 
651;  tellurium,  662;  tin,  694;  tungsten, 
695  ;  uranium,  694  ;  zinc,  684 
Oxyacids  of  sulphur,  the,  651 
Oxygen,  properties  of ;  tests  for,  593—598 
Ozone,  properties  of ;  production  of,  598 


Palladium,  705 
Papin's  digester,  606 
Paracelsus,  683 
Pasteur,  C02 


73^ 


INDEX. 


CHEMISTR  Y — continued. 

Pattinson’s  process  for  obtaining  silver  from 
lead,  698 
•Payne,  Mr.,  577 
Pearl  white.  669 
Pelopium,  694 
Pentad,  the  590 

Peroxide  of  hydrogen,  608  ;  do.  of  nitrogen, 
611 

Phosphane,  661 

Thosphide  of  hydrogen,  solid  and  liquid,  661 
Phosphorus,  sources  of ;  properties  of  red  and 
white  ;  processes  in  the  manufacture  of ; 
compounds  of,  660,  661 
Phosphuretted  hydrogen,  661 
Photography,  623 — 627 

Physical  properties  of  antimony,  668  ;  arsenic, 
663  ;  bismuth,  669 ;  iron,  691 ;  potassium, 
672  ;  sodium,  673  ;  zinc,  684 
“  Pig”  or  cast  iron,  687 
Pisani,  675 

Platinum,  sources,  properties,  oxides  of,  704 

Platinum  chloride,  705 

Plumbago,  black  lead,  or  graphite,  631 

Plumbum,  696 

Pneumatic  trough,  the,  595 

Polybasic  acids,  590 

Portable  sand  bath  and  oven,  664 

Positive  osmose,  584 

Potassic  silica  fluoride,  642 

Potassium  hydrate,  672 

Potassium,  sources,  physical  and  chemical 
properties,  oxides,  salts,  and  compounds  of, 
671—673 

Precipitating  glass,  for  argentic  chloride,  699 
Prefixes  and  terminations  in  chemical  nomen¬ 
clature,  588,  589 

Prentice  &  Co.,  Messrs.,  609,  612 
Preparation  of  sulphuretted  hydrogen,  653 
Pressure  cavities  in  the  topaz,  beryl,  and  dia¬ 
mond,  633 
Priestley,  Dr.,  593 

Prince  Consort’s  speech  on  Science,  the,  577 
Printing  process  in  photography,  625 
Processes  for  the  treatment  of  cast  iron  in  the 
manufacture  of  steel,  688 
Process  for  the  purification  of  native  sulphur, 

649 

Production  of  iodine  vapour  from  potassium 
iodide,  622 

Production  of  iron  in  Great  Britain,  the,  687 
Protohydrate  of  sulphuric  acid,  652 
Protoxide,  the,  589 
Puddling  iron,  process  of,  688 

Quartz,  various  kinds  of,  642 
Quicklime,  676 
Quicksilver,  609 

Quicksilver  bottle  of  wrought  iron,  594 
Rain-water,  605 

Rates  of  combustion  of  gun  cotton,  616 

Realgar,  663 

Red  phosphorus,  658 

Regnault,  579 

Reich,  694 

Reinsch’s  test  for  arsenic,  667 
Relative  amounts  of  oxygen  and  nitrogen  in 
air,  604 


CHEMISTR  Y — continued. 

Retort  fitted  to  a  series  of  Wolfe’s  bottles, 

619 

Reynolds,  Mr.,  582 
Rhodium,  705 
Richter,  694 
Ring  stand,  595 
River-water,  605 
Roberts,  Mr.,  675 
Rock  crystal,  643 
Rodwell,  Mr.,  George,  593 
Roscoe,  Professor,  592,  652,  670,  680 
Rubidium,  sources,  properties,  oxide,  and 
salts  of,  674 
Ruthenium,  703 
Rutherford,  Dr.,  600 


Safety  tubes  for  experiments  with  gases,  6iq 
Sal  ammoniac,  618 
Saltpetre,  672 

Salts  of  hydrogen,  590,  609 
Sand-blast  process  for  cutting  hard  sub¬ 
stances,  646 

Scheele,  Mr.,  593,  620,  653,  655,  692 
Scheerer,  669 
Schonbcein,  599,  609 
Schrotter,  Professor,  637 
“Schweinfurt  green,”  664 
Selenium,  sources,  properties,  oxides,  salts, 
and  compounds  of,  648 
Selenites  and  seleniates,  649 
Seleniuretted  hydrogen,  or  dihydric  selenide, 

649 

Sevres  porcelain,  678 

Siemens’s  induction  apparatus,  599 

Silica,  crystals  of,  642 

Silicon,  sources  of,  amorphous,  graphitic,  and 
crystalline,  oxides  and  combinations  of, 
641 — 648 

Siliciuretted  hydrogen,  643 
Silver,  sources,  properties,  oxides,  saltsof,  and 
tests  for,  698 — 702 
Simpson,  Mr.  G.  Wharton,  626 
Smelting  iron  ore  in  India,  673 
Soda-water,  635 
Sodic  chloride,  673 

Sodium,  sources,  physical  and  chemical  pro¬ 
perties,  oxides,  and  salts  of;  to  detect  the 
presence  of,  673,  674 
Soft  water,  605 
Sonstadt,  Mr.  Edward,  680 
Sorby,  Mr.,  on  the  cavities  in  diamonds,  634 
Sources  of  ammonia,  618  ;  arsenic,  663  ;  car¬ 
bon,  631  ;  iron,  685  ;  phosphorus,  655 
Specific  gravity  of  solids,  of  liquids,  and  of 
gases  ;  to  ascertain  the,  579 
“  Speiss,”  693 
Spiller,  Mr.  John,  623 
Spontaneous  generation,  6or 
Standard  for  determining  the  weight  of  dif¬ 
ferent  substances,  579 
Steel,  687 — 691 

Streeter’s  machine-made  jewellery,  706 
Strontianite,  676 

Strontium,  properties,  oxides,  and  salts  of, 
676,  677 

Subliming  apparatus  for  purifying  crude  sul¬ 
phur,  649 

Sulphides  of  arsenic,  663 


INDEX. 


737 


CHEMI3TR  Y  —continued. 

Sulphur,  sources  of ;  properties  of ;  uses  in 
commerce  ;  oxides  of ;  oxyacids  of ;  com¬ 
pounds  of ;  the  purification  of,  649 — 654 
Sulphuretted  hydrogen,  653 
Swan,  Mr.,  627 
Swedenborg,  593 
Symbols,  table  of  the,  589,  591 
Synthesis  of  the  elements  forming  water,  607 


Table  of  the  different  qualities  of  gold  manu¬ 
factured  in  different  parts  of  the  world,  709 
Table  of  the  nomenclature  and  symbols  of 
binary  compounds,  589 
Table  of  the  symbols,  and  old  and  new  com¬ 
bining  or  atomic  weights  of  the  elements, 

Talbot,  Hon  H.  Fox,  623 
Talbotype,  the,  623 
“  Tartar  emetic,”  668 

Tellurium,  its  analogy  to  sulphur  and  sele¬ 
nium,  oxides,  and  properties  of,  662 
Telluretted  hydrogen,  662 
Tennant,  Professor,  702 

Terms  used  to  denote  the  equivalents  of  the 
elements  in  compound  with  hydrogen,  590 
Test-tubes  and  rack,  594 
'Testing  operations  for  arsenic,  6f  5 
'Tests  for  iodine,  623 ;  oxygen,  598 ;  ozone, 
599  ;  salts  of  potassium,  673  ;  silver,  699 
Tetrachloride  of  platinum,  the,  705 
'Tetrad,  the,  590 
'Thallium,  696 
Theory  of  fermentation,  602 
Tilghman,  B.  C.,  646 

Tin,  sources  whence  derived,  use  in  commerce  ; 

oxides  and  alloys  of,  694 
“Tin  foil,”  694 
“  Tin  glass,”  669 
Tomlinson,  Professor,  579 
Tomlinson’s  cohesion  figures,  580 
'Triad,  the,  590 
Tri-nitro-glycerine,  616 
Trioxide,  the,  589 
Troostwick,  638 

Tubes  for  experimenting  with  arsenic,  665 
'Tungsten,  oxides  of ;  use  in  commerce,  695 


Uranium,  sources  of ;  oxides  and  salts  of ; 
uses  in  commerce,  693 


CHEMISTR  Y  —continued. 

Useful  forms  of  furnaces,  with  sand  bath  and 
oven,  667 

Use  of  the  Sneider  rifle  in  the  battle  preced¬ 
ing  the  fall  of  Magdala,  697 


Vacuum  pans,  703 
Valentine,  Basil,  668 

Various  blowpipes  used  by  chemists  and 
mineralogists,  665 

Various  gas  burners  used  for  heating  pur¬ 
poses,  595 
Vauquelin,  655,  693 
Ventilation  of  gun  cotton  factories,  611 
Vertue,  George,  654 
Vital  air,  594 
Vitality,  586 


“  Warder,”  601 
Water,  605 — 608 
Water-glass,  642 

Water,  different  degrees  of  purity  in,  605 
Water,  why  selected  as  the  standard  for  de¬ 
termining  the  specific  gravity  of  liquids 
and  solids,  578 
“  Weight,”  578 
“  Weissmatte,”  669 
Werner  crystals,  643 
“What  are  bacteria?”  601 
Whitestone,  643 
Witherite,  677 

Wohler  and  Deville's  directions  for  the  pre¬ 
paration  of  amorphous  boron,  639 
Wohler  and  Deville’s  method  of  converting 
amorphous  into  crystallized  boron,  639 
Wollaston,  Dr.,  704 
Wood,  704 

Wopdbury,  Mr.  Walter  B  ,  627 
Woodburytypes,  627 
Wood  charcoal,  631 
Woodward,  Mr.,  582 
Wrought  iron.  687 


Zinc,  sources  of ;  physical  and  chem'cal  pro¬ 
perties  ;  oxides  and  salts  of,  683 
Zinc  casting,  French  Exhibition,  683 
Zinc  white,  684 


ORGANIC  CHEMISTRY 

Analysis  the  ruling  power  in  organic  che¬ 
mistry,  71 1 

Analysis  of  an  inorganic  salt,  71 1  ;  do  of  an 
organic  body,  71 1 

Apparatus  lor  organic  analysis,  713 


Ballard,  715 


ORGANIC  CHEMISTRY  -  continue'}. 

Coffee-berry,  proximate  and  ultimate  consti¬ 
tuents  of  the.  71 1 

Cooper,  Mr.  John  Thomas,  713 

Exposure  of  animal  substances  to  water  gas 
at  a  high  temperature,  7x4  ;  blood,  715  :  al¬ 
bumen,  716  ;  the  body  of  a  toad  in  carbon, 

47 


738 


INDEX. 


ORGANIC  CHEMISTRY— continued. 

16 ;  the  body  of  a  frog  in  sand,  716 ;  the 
ody  of  a  frog  in  plaster  of  Paris,  717  ;  the 
body  of  a  fish  in  plaster  and  alum,  717  ;  an 
oyster-shell  in  do.,  718 


Fossils,  718 


Gerhardt,  713 


Iron  flask  used  in  Dr.  Richardson’s  experi¬ 
ments,  715 


Laurent,  713 
Liebig,  713 


Organic  chemistry,  711 — 718 


ORGAN  IG  CHEMISTRY — continued. 

Organic  compounds  which  are  not  organized, 
711 


Payen,  711 


Richardson’s,  Dr.  B. ,  experiments  in  organic 
decomposition,  713 


I  Sedgwick,  Dr.,  715 

Tubes  and  bulbs  employed  in  organic  analy¬ 
sis,  713 


Vulcanizing  apparatus  used  in  Dr.  Richard¬ 
son’s  experiments,  714 


mMIm 

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